8 Late Cenozoic Glaciations in Patagonia and Tierra del Fuego

Transcription

Els AMS
LPCT
00008
22-1-2008
14:06
Page:151
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
8
03
04
Late Cenozoic Glaciations in Patagonia and Tierra del Fuego
05
06
Jorge Rabassa
07
08
CADIC-CONICET, C.C.92, 9410 Ushuaia, Argentina and Universidad Nacional de la Patagonia at Ushuaia
09
10
11
erosional surfaces (Kaplan et al., 2004; Singer et al.,
2004a). In some cases, the magnetostratigraphy of glacial
deposits is available, thus allowing the correlation with
the Pampean (central eastern Argentina; Fig. 1a) continental sequences (mostly loess units) and with the global
ocean record (Rabassa et al., 2005).
Likewise, the stratigraphic and biostratigraphic units
of the Pampean Region of Central Argentina have been
chronologically linked by means of paleomagnetic dating
techniques, thus providing a basis for regional and planetary correlation between the glacial events and the
Pampean loess deposition (Cione and Tonni, 1999).
The regions discussed in this chapter are shown in
Fig. 1. Argentinian Patagonia extends southward of the
Rı́o Colorado (Fig. 1b, Site 1), with a total length of almost
2500 km, between 36 and 55 S, on the eastern side of the
Andean Cordillera, including Isla Grande de Tierra del
Fuego (Fig. 1c). If a map of Patagonia is superimposed
in an upside-down position on top of a map of Europe at
the same scale, its extremes would be coincident with the
latitudes of the island of Malta and Copenhagen, respectively, a very large distance that explains the great variety
of climates and ecosystems of this region.
This chapter includes also the most significant information available on the glaciations of the Chilean (western) side of the Andes, along the same latitudinal belt. It
deals particularly with the Chilean Lake District (Fig. 1b,
Sites 13, 14), where very important work has been done
by several authors during more than three decades
(Mercer, 1976; Porter, 1981; Denton et al., 1999a, b).
Patagonia is formed by two main physiographical
units: the Patagonian Andes (Fig. 1a), which extend in a
N–S direction, except in Tierra del Fuego where they turn
eastward to achieve a W–E arrangement, and extraAndean Patagonia, mostly low-lying, semiarid flat
terrains, volcanic tablelands and low ridges of varied
geological composition.
The localities cited in the text are found along the
Patagonian and Fuegian Andes between 38 and 55 S,
and the corresponding Patagonian plains, the Fuegian–
Magellanic Basin and the adjacent Chilean areas (Fig. 1a).
1. Introduction
12
13
Patagonia and Tierra del Fuego show one of the longest
and most complete sequences of glacigenic deposits and
landforms in the Southern Hemisphere outside of
Antarctica and, perhaps, of the entire world. Starting in
the latest Miocene, these units have been preserved,
though sometimes rather in a fragmentary manner, thanks
to their interbedding with volcanic flows that have protected the sediments from erosion, besides allowing their
absolute dating. Similarly, the relative tectonic stability
of the area, after the final emplacement of the southern
Andes, and the dry climate that has dominated the region
since the Late Miocene have contributed to keep the
glacigenic deposits from denudation.
The climate of Patagonia and Tierra del Fuego, following the general conditions on the Earth, has suffered
significant variations during the Cenozoic, particularly
since the Miocene. These climatic changes are related
to various causes such as continental displacement due to
plate tectonics, modification on greenhouse gases content
in the lower atmosphere and changes in astronomical
parameters, namely eccentricity of the Earth orbit, obliquity of the planetary axis and equinoccial precession.
Though this process of climate deterioration was
initiated possibly toward the end of the Mesozoic, but
most likely, at the beginning of the Paleogene, it culminated with the recurrence of multiple cold-warm climatic
cycles starting in the Miocene, which led to the development of global ice ages.
The knowledge of the Late Cenozoic glaciations in
Patagonia and Tierra del Fuego (Fig. 1a) has made significant progress in the last decade, thanks mainly to the
application of absolute dating techniques, following the
pioneer work of John Mercer (Mercer, 1976, among many
other benchmark contributions; Meglioli, 1992; Clapperton,
1993; Ton-That et al., 1999; Singer et al., 2004a). The cited
dating techniques have allowed to link the Patagonian
records with other glaciated regions and with the global
marine isotopic sequence (Shackleton, 1995).
This chapter presents the status of our knowledge on
the Patagonian and Fuegian glaciations, starting in the
Late Miocene, when the junction of global, cooler climatic conditions and the final rise of the southern Andes
enabled the formation of mountain glaciers in the area.
The objective of this chapter is to present the absolute
chronology of the Patagonian terrestrial glacial
sequences, basically dated by means of 40Ar/39Ar dating
techniques on volcanic rocks associated with glacial
landforms and deposits, and more recently, cosmogenic
isotope dating techniques on erratic boulders and glacial
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
2. Glaciers in Patagonia and Tierra del Fuego
Patagonia and Tierra del Fuego are some of the regions of the
world still largely covered by ice and snow. Three major
mountain ice sheets can be observed along the Patagonian
and Fuegian Andes, several smaller ones and countless
cirque and niche glaciers and permanent snowfields of varied
size. These three ice sheets are the Northern Patagonian
2008 ELSEVIER B.V.
ALL RIGHTS RESERVED
DEVELOPMENTS IN QUATERNARY SCIENCES
VOLUME 11 ISSN 1571-0866
151
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
1 Color Lines: 62 Chap. Open : Recto
Els AMS
LPCT
00008
152
22-1-2008
14:06
Page:152
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Ice Field (46300 –47300 S; 73–74 W), the Southern
Patagonian Ice Field (48300 –51 S; 73–74 W) and the
Darwin Cordillera Ice Field (54300 –55 S; 69–71 W). See
Fig. 1a. These large ice bodies are, by far, the most important
of the Southern Hemisphere outside Antarctica. They are
the remnants of the Late Pleistocene mountain ice sheet
that covered the southern Andes. This Pleistocene ice sheet
had a total length of almost three times the size of
the coeval European Alpine ice sheet, but elongated in a
01
02
03
04
05
06
07
08
09
N–S direction, allowing for significant changes in glacier
type, size, volume, elevation, regime and climate.
Local ice caps of much reduced dimensions are found
usually at the summit of Tertiary and Quaternary volcanoes, that is, endogenetic, constructional features that
have grown above the regional summit accordance
surface. Examples of these local ice caps are those on
Volcán Lanı́n (39300 S; 71300 W, 3778 m a.s.l.; Fig. 1b,
Site 17; Fig. 2), Monte Tronador (41300 S; 71500 W;
10
11
12
(a)
13
14
15
28
31
32
33
34
35
36
TAITAO
Hielo PENNINSULA
Patagónico
Norte
NORTHERN
PATAGONIAN
ICE FIELD
37
38
39
40
41
42
Hielo Patagónico Sur
SOUTHERN
PATAGONIAN
ICE FIELD
43
44
45
S O U T H E R N
30
Valdes penninsula
O
Chiloe Is.
ISLA
CHILOÉ
29
LOCATION MAP
San Matías gulf
CHUBUT
PROVINCE
TH
AM
ER
ICA
27
RIO NEGRO
PROVINCE
San Jorge gulf
SO
U
P A C I F I C
26
Bahía Blanca
NEUQUEN
PROVINCE
A
25
S
I
24
PA
N
23
M
G
22
PA
A
21
G
AR
I
T
20
T
EN
BUENOS AIRES PROVINCE
NA
SANTA CRUZ
PROVINCE
A
19
H
ATLANTIC OCEAN
ATLANTIC OCEAN
P
18
C
E
A N D E S
17
IL
CORD
ILLER
A DE L
CHILE
A COS
AN LA
TA
KE DI
STRIC
T
O C E A N
16
46
47
MALVINAS/FALKLAND Is.
48
XII REGION
MAGELLAN STRAITS
TIERRA DEL
FUEGO PROVINCE
de
M
51
ag
50
al
la
ne
s
49
PACIFIC OCEAN
53
ISLA
RIESCO
54
55
Es
tre
ch
o
52
ISLA GRANDE DE
TIERRA DEL FUEGO
ISLA DE LOS ESTADOS
56
DARWIN CORDILLERA
Darwin Cordillera
icefield
57
58
CAPE
HORN
59
DRAKE
PASSAGE
60
Fig. 1. Location maps. (a) Patagonia, main geographical regions; (b) Patagonia, location of localities cited in the text
(see attached list); (c) Tierra del Fuego, localities cited in the text.
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
22-1-2008
14:06
Page:153
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
(b)
01
02
03
10
11
12
4
1
8
P A C I F I C
16
10
16
9
12 15
21 20
14
20
21
22
23
24
19 22
5
25
SAN JORGE
GULF
24
30
31
32
33
34
1
3
31
35
37
45
33
ATLANTIC OCEAN
44
ATLANTIC OCEAN
25
43
36
23
26
29
35
A
NORTHERN
PATAGONIAN
ICE FIELD
Hielo
Patagónico Sur
SOUTHERN
PATAGONIAN
ICE FIELD
29
42
34
28
T
6
Hielo
Patagónico
Norte
27
P
26
PENÍNSULA
VALDÉS
G
19
LOCATION MAP
FIGURE 1b
SAN MATÍAS GULF
A
18
7
18
Chiloe Is.
17
2
17
13
15
S
3
13
14
P
PA
41
28
32
36
MALVINAS/FALKLAND Is.
27
ne
s
37
AM
ER
ICA
09
AR
11
AM
SO
UT
H
08
GE
NA
A
07
C
I
NT
I
06
H
E
IL
N
05
O
O C E A N
04
39
al
la
38
MAGELLAN STRAITS
M
ag
39
42
ISLA
RIESCO
43
o
ISLA GRANDE DE
TIERRA DEL FUEGO
ch
38
30
PACIFIC OCEAN
Es
tre
41
de
40
46
44
40
45
ISLA DE LOS ESTADOS
DARWIN CORDILLERA
Darwin Cordillera
icefield
46
CAPE
HORN
47
48
DRAKE
PASSAGE
49
1.
2.
3.
4.
5.
6.
7.
8.
9.
Río Colorado
Río Negro
Río Limay
Río Neuquén
Río Chubut
Río Deseado
Río Collón Curá
Río Aluminé
Lago Nahuel Huapi and
San Carlos de Bariloche
10. Lago Traful
11. Volcán Copahue
12. Monte Tronador
50
51
52
53
54
55
56
57
58
59
13. Lago Llanquihue and
Chilean Lake District
14. Puerto Montt and Monteverde
Archaeological Site
15. Lago Mascardi
16. Río Pichileufú
17. Volcán Lanín and Río Malleo
18. Lago Huechulaufquen and
San Martín de los Andes
19. Epuyén and Cholila
20. El Maitén
21. El Bolsón and Lago Puelo
22. Esquel, Portezuelo de Apichig
and Portezuelo de Leleque
23. Río Santa Cruz
24. Lago Buenos Aires and
Meseta Lago Buenos Aires
25. Lago Viedma
26. Lago Argentino
27. Río Gallegos
28. Cerro del Fraile and Lago Roca
29. Perito Moreno and Upsala Glaciers
30. Torres del Paine National Park
31. Punta Arenas and Península
Brunswick
32. Monte San Lorenzo
33. Puerto Natales
34. Volcán Reclus
Fig. 1. Continued.
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
Volcán Hudson
Volcán
Mylodon Cave
Seno Skyrring
Seno Otway
Beagle Channel and Ushuaia
Cóndor Cliff
Town of Perito Moreno
Tres Lagos
Lago Cardiel and Río Shehuen
Lago San Martín
Península Mitre
153
Els AMS
LPCT
00008
154
22-1-2008
14:06
Page:154
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
(c)
01
02
SANTA CRUZ
PROVINCE
(ARGENTINA)
PATAGONIA
03
04
N
05
06
Cabo Vírgenes
Cabo Espíritu Santo
Primera Angostura
XII REGION (CHILE)
07
Atlantic Ocean
Segunda Angostura
08
its
09
14
15
CHILE
an
PENINSULA
BRUNSWICK
16
ARGENTINA
PUNTA
ARENAS
13
gell
12
Cabo Nombre
Punta Páramo
Bahía San Sebastián
Cabo San Sebastián
Punta Sinaí
Ma
SENO
OTWAY
11
Stra
10
útil
a In
í
Bah
ISLA
17
GRANDE
Cabo Doming
DE
Río Grande
18
Cabo Peñas
Almir
PARQUE NACIONAL
TIERRA DEL FUEGO
anta
zgo
Cabo San Pablo
Río San Pablo
Río Lainez
Cabo Irigoyen
Río Irigoyen
22
Lago Fagnano
23
DARWIN
25
B.Lapataia
26
Península Mitre
Puerto Williams
re
gg
Slo
et
29
uir
hía
I. Picton
Ag
Ba
Isla Navarino
Isla Hoste
28
o
rt le arr
t
be b v
oa
ar Ga Na
M
H
a
t
. la n
ta
a
s
u
n
E I P
Pu
hía
Beagle Chan
55° S
A
Cabo
San Diego
on
Ba
nel
27
Tolhuin
a
ivi
Ol nda lino
Valle Carbajal
o
o
gu
Rí
Glaciar Martial
Ushuaia ta Se Rem anza
.
n
lm
Pu Ea
.
CORDILLERA
24
Le M
aire
Seno
21
it of
20
Stra
TIERRA DELFUEGO
19
Pacific Ocean
30
I. Lennox
I. Nueva
31
32
33
70° O
34
Cape Horn
35
Fig. 1. Continued.
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
AU1
53
54
55
3556 m a.s.l.; Fig. 1b, Site 12; Fig. 3; see Rabassa et al.,
1978, 1981), Monte San Lorenzo (47450 S; 72150 W;
3706 m a.s.l.; Fig. 1b, Site 32) and Isla Riesco (53140 S;
3000 W; 1183 m a.s.l.; Casassa et al., 2002a, 2002b;
Fig. 1a), among many others, particularly on the Chilean
side of the Andes.
Hundreds of smaller cirque and short valley glaciers
can be found elsewhere in the Patagonian and Fuegian
Andes. Due to the impact of global warming (Rosenbluth
et al., 1997), most of these mountain glaciers have been
receding very intensively in the last two decades, and it is
very likely that most of them will be totally gone by the
middle of the present century (Casassa, 1995; Naruse et al.,
1995; Aniya et al., 1997; Aniya, 1999; Rivera and Casassa,
2004; Rabassa, 2007). The loss of ice will have drastic effects
on many environmental issues, such as water resources
(Coudrian et al., 2005; Rabassa, 2007) and sea level rise
(Rignot et al., 2003).
56
57
3. Snowline Position and Distribution of Past
and Present Glaciers
58
59
60
The permanent snowline or firnline is the line that connects the lowest topographical positions of snow fallen
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
during the previous winter on the surface of a glacier that
has not melted away at the end of the Southern Hemisphere summer, that is, March and early April. The
equilibrium line is an imaginary line that separates
the accumulation area, with a net gain of mass, from
the ablation area (net loss of mass) on the surface of a
glacier. Permanent snowline and equilibrium line are
coincident in most maritime and temperate glaciers
(Clapperton, 1993). These lines differ only in polar or
subpolar regions, where regelation takes place below the
permanent snowline. Regional snowline, or equilibrium
line altitude (ELA), is a very important geographical and
climatic parameter in Patagonia, which tends to be very
stable through time for a certain area as it is related to the
position of the summer 0C isotherm. However, recent
climatic change due to global warming has determined a
significant rise in ELA in most of the studied area, with a
rise of up to 200 m in only the last 20 yrs (Casassa et al.,
2003; Rabassa, 2007).
The snowline and ELA and the distribution of modern
ice bodies have been discussed extensively by Clapperton
(1993). The altitudinal position of snowline is highly
dependent on local topographic and climatic conditions.
The snowline decreases gradually from North to South,
between around 2200 m a.s.l. in northern Patagonia and
Els AMS
LPCT
00008
22-1-2008
14:06
Page:155
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
155
In northern Patagonia, between 36 and 44 S, the
position of present and past snowline has been studied
by Flint and Fidalgo (1964, 1969) and Rabassa et al.
(1980). Present ELA has been estimated by means of a
detailed glacier inventory, based on aerial and terrestrial
photographs, completed in 1978 (Rabassa et al., 1980).
Pleistocene ELA has been calculated using the cirque
floor elevation, assuming that these cirques (presently
with or without ice) have been reoccupied several times
during the Quaternary (Flint and Fidalgo, 1964, 1969). In
the region of temperate regime and dominant winter
precipitation, the position of the ELA is roughly coincident with the atmospheric summer 0C isotherm,
but further south, increased year-round precipitation
brings ELA to much lower positions, reaching as low
as 800 m a.s.l. in western Tierra del Fuego (Clapperton,
1993), around 1000 m a.s.l. in Ushuaia (Fig. 1b, Site 40;
Coronato, 1995a, b) and possibly in between 500 and
900 m a.s.l. at Isla Riesco (Fig. 1a; Casassa et al., 2002b).
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
4. Glaciations in Patagonia and Tierra del Fuego
22
23
24
25
26
27
28
Fig. 2. Volcán Lanı́n (39300 S; 71300 W, 3778 m a.s.l.;
Fig. 1b, Site 17), southern slope, facing Lago
Huechulauquen (Fig. 1b, Site 18), province of Neuquén,
Argentina. (Photo by J. Rabassa, 1983).
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Fig. 3. Monte Tronador (41300 S; 71500 W; 3556 m a.s.l.;
Fig. 1b, Site 12), western slope. Seen from Casa Pangue
Glacier valley, western slope, Chile. (Photo by J. Rabassa,
1979).
51
52
53
54
Pliocene and Pleistocene glaciations were frequent in this
region. Moreover, glacial tills of a latest Miocene glaciation
have been found in southern Patagonia, and indirect evidence points at, at least, isolated mountain glaciers already
in Late Miocene times, both in northern and southern Patagonia. Pliocene glaciations have been recorded in northern
North America (northwest Canada, Alaska) as of Late
Gauss paleomagnetic age (Barendregt and Duk-Rodkin,
2004; Duk-Rodkin et al., 2004; Harris, 2005), and as old
as 2.5 Ma in central Missouri, USA (Balco et al., 2005).
It is considered that valley and piedmont glaciers
coming from the ice sheet or from local ice caps extended
up to several hundred kilometers eastward during the
most extensive glaciation, as well as to the deep Pacific
Ocean waters in the west. The present Atlantic submarine
platform was reached by the ice several times during this
period, but only south of the present Rı́o Gallegos valley
(Fig. 1b, Site 27). On most of the Argentinian side of the
Andes, the glaciers only extended to the piedmont areas,
not far beyond the mountain front. On the western side
south of Isla Chiloé (Fig. 1a), the ice probably calved into
the Pacific Ocean during glacial events.
It should also be noted that the total length of the
Pleistocene Patagonian Mountain Ice Sheet was almost
three times the extent of the European Alps ice cap and
more than five times that of the New Zealand Alps during
the same period.
4.1. The History of Glacial Investigations
in Patagonia and Tierra del Fuego
55
56
57
58
59
60
61
62
less than 1000 m a.s.l. in the western Fuegian Andes. Its
altitude increases sharply from West to East, as a consequence of the strong precipitation gradient in this direction, generated by the interference of the Andean
mountain chains with the weather coming from the
AU2 South Pacific anticyclonic center (Chapter 3).
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
The first scientific observations about Patagonian glaciations were presented by Charles Darwin who, during the
famous ‘‘H.M.S. Beagle’’ voyage and together with
Robert Fitz Roy, explored the Rı́o Santa Cruz valley
(Fig. 1b, Site 23) in 1833. There, Darwin described
erratic boulders at Cóndor Cliff and several other sites
along this valley (50 S; 71 W; Fig. 1b, Site 41), very far
Els AMS
LPCT
00008
156
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
AU3
28
29
30
31
32
22-1-2008
14:06
Page:156
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
from the Andean ranges, to which he assigned a glacial
origin though interpreting them as the product of iceberg
deposition, as it was the paradigma of those times
(Darwin, 1842; Imbrie and Imbrie, 1979). This was the
first paper ever published on the Patagonian glaciations
and probably one of the very first after the publication of
Louis Agassiz’s glacial theory in 1840 (Imbrie and
Imbrie, 1979), though Darwin’s actual observations preceded it by several years.
Several decades later, the famous Swedish geologist
and explorer Otto Nordenskjöld (1899) made the first
scientific study of the Patagonian and Fuegian glaciations, at both ends of the Pleistocene ice sheet, around
San Carlos de Bariloche (41 S; Fig. 1b, Site 9) and in
Tierra del Fuego. Nordenskjöld followed the original
work of Francisco P. Moreno (1897) who, during his
exploratory work in the Patagonian Andes, made very
early and significant observations about the nature and
extent of the glaciations. Nordenskjöld (1899) provided
the first detailed map of the extension of the Quaternary
glaciations in southernmost Patagonia and Tierra del
Fuego (Fig. 4), and recognized different moraines,
which he correctly interpreted as representing several
glacial stages. He was the first to suggest that the ice
had partly extended over the present submarine platform.
Other important contributions of this pioneer epoch are
those by Wehrli (1899), Rovereto (1912) and Willis (1914).
In the first decades of the twentieth century, Patagonia
was visited by many European scientists, who provided
the bases of our knowledge of the region. Vaı̈no Auer, a
Finnish geographer, over several decades explored extensive areas of Patagonia. His contributions (Auer, 1956,
1958, 1959, 1970, among many other papers) are an outstanding catalogue of field localities and sections. Unfortunately, his interpretations about the extent of the
glaciations were biased by the influence of Czajka
(1955) who proposed a total glacierization of Patagonia,
a model that we now know to be incorrect. Auer (1970)
partially revised these ideas of a totally ice-covered Patagonia, but he still insisted in local glaciations in the central
Patagonian massifs, for which proof has never been found.
The maximum extent of the different glacial advances
was first presented full scale by Carl C:zon Caldenius, a
Swedish geologist who, between 1928 and 1931, mapped
the glacial deposits and landforms of Patagonia (Fig. 5).
Caldenius’ academic advisor at Stockholm University was
the famous glacial geologist Gerard De Geer. The latter had
asked Dr José M. Sobral, an Argentinian member of Otto
Nordenskjöld’s 1901–1903 Antarctic Expedition and as his
geology student graduated at Uppsala University, and who
was by that time the Head of the Argentinian Geological
Survey, to support the study of Patagonian glaciations, in
the same way as it had been done on the Scandinavian
Peninsula. Mostly, De Geer’s interest was to compare glacial varve sequences in both hemispheres, the early chronological tool that he had developed for the Scandinavian
Peninsula. De Geer (1927) described in detail this binational arrangement and presented the first preliminary data
of Caldenius’ expedition. A warm biography of Caldenius
has been presented by Lundqvist (1983, 1991, 2001).
In his paramount contribution, Caldenius (1932) presented a map that covered more than 1 M km2 (Fig. 6)
extending from Lago Nahuel Huapi (41 S; Fig. 1a, Site 9)
to Cape Horn (56 S; Fig. 1a). Caldenius (1932) identified
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
Fig. 4. Glacial map of Tierra del Fuego, by Otto Nordenskjöld (1899).
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
22-1-2008
14:06
Page:157
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Fig. 5. Carl C:zon Caldenius. (Photo by Jan Lundqvist;
Lundqvist, 1983, 1991, 2001).
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
Fig. 6. Caldenius’ (1932) original glacial map of Patagonia.
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
157
moraines corresponding to four glacial events which he
named ‘‘Initioglacial,’’ ‘‘Daniglacial,’’ ‘‘Gotiglacial’’ and
‘‘Finiglacial,’’ assuming a direct correlation with the Scandinavian glacial model. He considered these units as succesive recessional phases of the Last Glaciation (LG) and
observed, additionally, the existence of inner morainic
belts, younger than the Last Glacial Maximum (LGM),
which he named as ‘‘post-Finiglacial’’ advances. Although
his stratigraphic scheme is quite sound and his glacial map
is an outstanding work for its detail and precision, in spite
of the lack of appropiate maps and reliable roads at the
time, the chronostratigraphic scheme is unfortunately
wrong. Caldenius (1932) underestimated the age of some
of the morainic belts, most likely impressed by the excellent state of preservation of the landforms, even those
occurring in some of the outermost (and older) arcs. This
is due to the extremely dry climate of the Patagonian
steppes. Such a high degree of preservation would never
exist in the Scandinavian or Baltic regions, where no wellpreserved pre-LG moraines are known.
Later authors have provided new data and evidence in
support of Caldenius’ basic model, modifying only his
original chronology. Although the currently identified
boundaries of the different glacial advances are highly coincident with those mapped by Caldenius, the total number of
glaciations and their chronological correlation has changed,
based on absolute dating, new paradigms and interpretations. Nevertheless, his original terminology is still preserved, because it has a high value as unifying criteria for
the different glacial events throughout the region.
Caldenius (1932), following the methodology then
imposed by De Geer, studied varves and other glaciolacustrine deposits, and used them to telecorrelate glacial
events in Patagonia with those of Scandinavia. We know
today that these attempts were unsound, and therefore,
this methodology has been abandoned.
Groeber (1936) recognized correctly that the glaciers
in northern Patagonia never extended much beyond the
Andean foothills. In later works, Groeber (1952) proposed a fourfold glacial model, and extended the glaciation not only over all of Patagonia, but even to the
western Pampas, reconstructions that are today clearly
unacceptable. Most likely, Groeber was strongly influenced by the works of Czajka and Auer, thus changing
his original, correct points of view. Unfortunately,
Groeber’s last works and his immense prestige among
Argentinian geologists for a long time delayed a proper
understanding of the real extent of glaciation. However,
his ideas were soon firmly opposed by Polanski (1965),
in his studies in the Andean piedmont of Mendoza, central Argentinian Andes (33–34 S, 300 km north of the
Patagonian northern boundary), who had a great influence on the later work of his student, Francisco Fidalgo.
Egidio Feruglio, an Italian geologist working for the
Argentinian government, had a deep knowledge of the
Patagonian regional geology and was, after Caldenius,
the great innovator in the study of the Patagonian glaciations. Feruglio (1944) described with great precision a
sequence of basaltic lava flows with interbedded tills
at Cerro del Fraile, Santa Cruz Province (51 S, Fig. 1b, Site
28), just north of the Magellan Straits, recognizing the
great antiquity of the glacial deposits and assigning them
AU4
Els AMS
LPCT
00008
158
22-1-2008
14:06
Page:158
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
a Pliocene age, older than the maximum glacial extent
(which was later known as the ‘‘Great Patagonian Glaciation’’ or GPG; Mercer, 1976). This was certainly an
extraordinary, pioneer contribution to the knowledge of
the Pre-Quaternary glaciations of Patagonia since absolute dating was then still unavailable, and at that time,
speaking about ‘‘Pliocene glaciations’’ was certainly a
revolutionary concept.
Years later, and working at the full regional scale,
Feruglio (1950) also recognized the existence of four
major Pleistocene glacial events, which he named as
‘‘Pichileufuense inferior,’’ ‘‘Pichileufuense superior,’’
‘‘Barilochense’’ and ‘‘Nahuelhuapense’’ (local names of
northern Patagonia, see Fig. 1b for type localities), retaining Caldenius’ (1932) fourfold scheme, but linking each
event to geomorphological positions that were indicators
of clearly different (and older) ages. Thus, he recognized
that the ‘‘Pichileufuense’’ landforms and sediments are
found on the topographical divides, whereas the deposits
of later glacial events are located within the valleys
excavated in them. Therefore, Feruglio (1950) established the basic criteria that much later allowed to identify a Quaternary ‘‘Canyon Cutting Event’’ (Rabassa and
Clapperton, 1990) in Patagonia. Likewise, he firstly
established the possible correlation of the glacial deposits
with (a) the ‘‘Rodados Patagónicos’’ or ‘‘Rodados
Tehuelches’’ (‘‘Patagonian Gravel Formation,’’ ‘‘Patagonian Shingle Formation’’; Darwin, 1842; Caldenius,
1940), which he considered to be of glaciofluvial origin,
and (b) the loess acumulation events in those regions
which he called ‘‘infraglacial’’, that is, the nonglaciated
Pampas of eastern central Argentina (Feruglio, 1950).
Richard F. Flint, the distinguished American Quaternary scientist at Yale University, was invited in the early
1960s by the Argentinian Geological Survey to work on
the Patagonian glaciations. Flint, together with Francisco
Fidalgo (Flint and Fidalgo, 1964, 1969), studied the glacial deposits in the northern Patagonian Andes (39–43 S;
Fig. 1a), proposing a threefold glaciation model, based on
what they named as the ‘‘Pichileufu,’’ ‘‘El Cóndor’’ and
‘‘Nahuel Huapi’’ drifts, which they considered to be phases
of the LG. However, they already suggested in their 1969
paper that the ‘‘Pichileufu Glaciation’’ might be older
than the Late Pleistocene.
Fidalgo and Riggi (1965) identified four main glacial
drifts at Lago Buenos Aires (47 S; Fig. 1b, Site 24), as
well as the glaciofluvial origin of at least a portion of the
‘‘Patagonian gravels,’’ but without assigning absolute
ages to the studied units.
John H. Mercer (Fig. 7), an English geographer working at Ohio State University, was a tireless explorer of the
Patagonian mountains, and he combined his work in
South America with simultaneous studies in Antarctica
and New Zealand. His knowledge of the South American
glaciations was unique for his times and his work was
probably not appreciated as it deserved. Mercer brought
new concepts and ideas to the problem of Patagonian
glaciations since 1969 (Mercer, 1969, 1972) and he was
the first to use modern techniques such as radiometric
techniques (K/Ar and 14C dating) and paleomagnetic
studies in glacial sequences. He put forward many original ideas, most of them confirmed by later work, and his
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
papers are a source of new research lines even today
(e.g. Mercer, 1972, 1976, 1983). Fleck et al. (1972) and
Mercer and Sutter (1981) studied many outcrops of glacial deposits interbedded with volcanic rocks, in which
radiometric and paleomagnetic dating techniques were
applicable, also restudying Feruglio’s (1944) Cerro del
Fraile Locality (Fig. 1b, Site 28). It was Mercer (1976)
who first chronologically established the existence of
Patagonian glaciations throughout the entire Quaternary
period, of frequent Pliocene glaciations and even of Late
Miocene tills, also recognizing the correlation of these
glacial episodes with global cold periods. He proposed a
four-glaciation model for the Chilean Lake District
(Fig.1b, Site 13) and demonstrated the ancient age of
the older glaciations (Mercer, 1976). In this work, he
gave the name of ‘‘Llanquihue Glaciation’’ to the last
Pleistocene glaciation [18O marine isotope stages (MIS)
4–2], a term later extended by Clapperton (1993) for the
entire South American continent, and coined the name
‘‘Great Patagonian Glaciation’’ (GPG) for the oldest and
outermost morainic complex.
Steve Porter (1981) identified also four major glaciations in the Chilean Lake District (39–41 S; Fig. 1b,
Site 13) and defined their chronology throughout the Pleistocene, using radiometric dating and relative age techniques. Paul Ciesielski and colleagues (1982) were the first to
present a correlation model for the Patagonian glaciations
with the erosional and depositional history of the Maurice
Ewing Bank (55 S), Southwestern Atlantic Ocean east of
Tierra del Fuego (Fig. 1a), based on Mercer’s (1976) chronostratigraphic scheme. In this model, the great antiquity of
the Patagonian glacial events and their relations with global
paleoclimatic episodes are confirmed. The pioneer work of
Edward Evenson and his colleagues from Lehigh University and other American universities since the mid-1980s
brought for the first time a modern approach to the study of
northern Patagonian glaciations on the Argentinian side of
the Andes, combining detailed field mapping, radiometric
dating and paleomagnetic studies (Kodama et al., 1985,
1986; Rabassa et al., 1986, 1990a; Schlieder, 1989; Rabassa
and Evenson, 1996).
Rabassa and Clapperton (1990) presented the first
review of the Patagonian glaciations and a general
Fig. 7. John H. Mercer at an outcrop of the Llanquihue
moraine with wood fragments, near Puerto Varas,
southern Chile. (Photo by J. Rabassa, 1973).
Els AMS
LPCT
00008
22-1-2008
14:06
Page:159
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
chronological correlation of all units known at that time.
Recently, Mörner and Sylwan (1989), Sylwan (1989),
Meglioli (1992), Wenzens (1999a, 1999b, 2000), Wenzens
et al. (1996), Schellmann (1998, 1999, 2003), Rabassa and
Coronato (2002), Strelin et al. (1999), Malagnino (1995),
Singer et al. (2004a, 2004b), and Sugden et al. (2005),
among many others, have stressed the great antiquity and
complexity of the Patagonian glacial sequence.
Chalmers Clapperton (1993) presented the first continental summary of our knowledge of South American
glaciations, including a complete description of those in
Patagonia, for the first time showing great detail on either
side of the Andes. His book is an outstanding compilation
of all the available information at that time, with a global
overview and correlation with other sectors of the Southern
Hemisphere as well as with the Northern Hemisphere.
Clapperton et al. (1995) expanded the investigations also
in southern Patagonia, in the Magellan Straits area (Fig. 1a).
Working in Patagonia since 1995, Bradley Singer
(University of Wisconsin) has introduced powerful tools
for the study of Patagonian glaciations. Detailed mapping
of extensive areas, profound volcanological research, the
wide use of 40Ar/39Ar dating on lava flows stratigraphically related with glacial deposits, careful paleomagnetic
studies with Laurie Brown and, more recently, together
with Robert Ackert and Michael Kaplan, the use of cosmogenic dating techniques on morainic boulders (Singer
et al., 1998, 1999, 2004a, b; Kaplan et al., 2004)
are significant contributions to the knowledge of Late
Cenozoic glaciations in southern South America.
Ton-That et al. (1999) proposed for the first time to
correlate the glacial sequences of Lago Buenos Aires and
Cerro del Fraile (Fig. 1b, Sites 24, 28) with the global
marine isotopic sequence, as presented by Shackleton
et al. (1990, 1995). A recent revision of the Patagonian
glaciations has been presented by Coronato et al. (2004a,
b), in which they indicated the development of the GPG
around 1 Ma, and evidence of (a) several pre-GPG
cold periods, between 7 and 2 Ma, (b) three post-GPGs
during the Early and Middle Pleistocene, (c) the Last
Pleistocene glaciation and (d) two main episodes of glacial
stabilization during the Late Glacial (15–10 14C ka BP). A
tentative correlation of glacial events with loess deposition
in the Pampas has been recently presented by Rabassa et al.
(2005).
In the last years, the activity of large, multidisciplinary
research groups focusing on certain geographical regions
has provided excellent studies on the chronology of Pleistocene glaciations of the Chilean Lake District (Denton
et al., 1999a, b; Fig. 1b, Site 13) and the LGM and
younger, Late Glacial recessional events and ice readvances in the Magellan Straits region (Sugden et al.,
2005, and other papers in the same volume; Fig. 1a).
These studies are clearly the model to be followed in
future studies of Late Cenozoic Patagonian glaciations.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
4.2. The Late Tertiary Glaciations in Patagonia
58
59
A significant amount of evidence suggests that the Patagonian Andes were already glaciated during Late Tertiary
times. Based on the concentration of d18O and other isotopes
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
159
found in Late Miocene Santa Cruz Formation carbonate
concretions, Blisniuk et al. (2006) have suggested that the
southern Patagonian Andes were uplifted >1 km, between
ca. 17 and 14 Ma, significantly enhancing aridity. Such
important uplift of the mountain belt would have brought a
large landmass above the regional snowline, adding to a
global cooling trend, forcing the development of at least
local ice caps at the mountain summits or upon huge composite volcanic cones, which were rapidly growing at that
time, as part of the same tectonic event.
From a neotectonic point of view, the final push
along the Liquiñe–Ofqui fault zone in southern Chile
(41–42150 S; Fig. 1a), associated with the arrival
and subduction of the Chilean Rise beneath the Taitao
Peninsula (Fig. 1a), generated a major denudation event
immediately before 5 Ma (Adriasola et al., 2005) and
probably the glacierization of the rising Andean summits.
Similarly, Thomson (2002) has applied fission track
thermochronology in the investigation of low-temperature
cooling and denudation history of the Patagonian Andes
along the southern part of the cited fault zone between 42
and 46 S. Enhanced cooling and denudation initiated in
the earlier part of the Late Miocene, between ca. 16 and
10 Ma, but much faster rates of cooling and denudation
took place after ca. 7 Ma and up to 2 Ma, being coeval
with the collision of the Chile Rise with the Peru–Chile
trench between 47 and 48 S and also with the initiation
of significant Patagonian glaciations. Thus, Thomson
(2002) stated that glacial and periglacial erosion processes
would have been the main contributors to denudation
already since ca. 7 Ma.
A latest Miocene age for the first Patagonian glaciations is also supported by carbon isotopic data on tooth
enamel (Cerling et al., 1997). These authors suggest that
a global decrease in atmospheric CO2 took place between
8 and 6 Ma, enabling an expansion of C4 photosynthesis
plants. This lowering of CO2 is compatible with global
glaciation, as it has been demonstrated for the LGM.
Supporting data from Tierra del Fuego have been published by Cerling and Harris (1999).
Glaciations of the Latest Miocene–Early Pliocene
In the northern margin of the Meseta del Lago Buenos
Aires (47 S, Fig. 1a, Site 24), which is entirely covered
by volcanic rocks, till deposits over 30 m in thickness are
found interbedded with basalt flows (Mercer, 1976;
Clapperton, 1993; Fig. 8). Mercer (1976) and Mercer
and Sutter (1981) obtained whole-rock K/Ar ages on the
under- and overlying lavas of 7.34 + 0.11 to 6.75 + 0.08
and 5.05 + 0.07 to 4.43 + 0.09 Ma, respectively, which
most likely assigns a Latest Miocene age for these glacial
deposits (Busteros and Lapido, 1983; Ardolino et al.,
1999). This allows these deposits as belonging to some
of the oldest Late Cenozoic glacial events in Patagonia,
and indicates that the Patagonian Andes in those times
were bearing at least isolated ice caps with outlet glaciers
that were clearly extending more than 30 km east
of the mountain front. In the same locality, Ton-That
et al. (1999) obtained 40Ar/39Ar (incremental-heating
technique) ages of 7.38 + 0.05 Ma for the underlying
Els AMS
LPCT
00008
160
22-1-2008
14:06
Page:160
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
02
03
04
05
06
07
08
09
10
11
12
13
(a)
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
(b)
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
(c)
44
Fig. 8. Latest Miocene–earliest Pliocene till at Meseta
Lago Buenos Aires (Fig. 1b, Site 24), Santa Cruz
Province, Argentina (Mercer, 1976; Ton-That et al., 1999).
(a) Location of till in between lava flows; (b, c) till and
striated glacial boulder (Photos by Bradley Singer, 1996).
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
AU5
62
Font: Times
flow and of 5.04 + 0.04 Ma for the overlying flow,
confirming in general terms the probable Latest Miocene
(or, at most, Miocene–Pliocene boundary) age of this first
preserved Patagonian glaciation.
Four basalt flows dated by 40Ar/39Ar (incrementalheating) techniques between 10 and 6.7 Ma have overlying
tills and three other ones with underlying tills have been
dated between 4.9 and 4.3 Ma at the Lago Buenos Aires
region. Additionally, no till was found below the Meseta
Guanabara Basalt, Lago Buenos Aires (Fig. 1b, Site 24),
dated at 9.87 Ma (Ton-That et al., 1999). Though the
absence of evidence should never be considered as the
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
evidence of absence, the Meseta Guanabara is located in
an area that should have been glaciated if the glaciers had
extended away from the Patagonian Andes before that age.
No precise, absolute ages may be yet assigned to those tills
overlying the basalts, but their comparison with the global
paleomagnetic sequence indicates that they could correspond to the C3 (a and b) Chron. During this period, the
oceanic sequences (Opdyke, 1995; Shackleton, 1995)
locate the strongest thermal lowering between 5.7 and
5.9 Ma, a period which is comprised between the limiting
ages of these tills. This correlation allows to suggest that at
least a major extra-Andean glaciation could have taken
place in southern Patagonia between isotopic stages TG 20
and TG 22, during the Gilbert Chron.
Schlieder (1989) had already recognized very coarse
diamictons along the Rı́o Aluminé valley, northern Patagonia (Fig. 1b, Site 8), and he assigned them to Late Miocene
glacial events, based on whole-rock K/Ar ages of the limiting basalts. He additionally proposed that the Alicurá Formation, originally assigned to the Lower Quaternary by
Dessanti (1972) and later, as the Alicurá Member of the
Caleufu Formation, to the Miocene–Pliocene (González
Dı́az et al., 1986), actually corresponds to the Late Miocene,
its upper age limited by overlying basalts dated at
6.41 + 0.13 and 5.26 + 0.14 Ma, respectively. In this interpretation, the Alicurá Formation would be the distal glaciofluvial unit of the Latest Miocene Patagonian Andean
glaciations, whose water and sedimentary discharge would
have been concentrated by the Rı́o Aluminé and the Rı́o
Collón Curá (Fig. 1a, Site 7), both tributaries of the paleoRı́o Limay, a main regional stream of the Atlantic slope
already in those times (Rabassa, 1975; Fig. 1b, Site 3). The
interpretation of a glaciofluvial origin for the Alicurá Formation related to ancient glaciations was already proposed
by Gracia (1958), though no absolute ages were then defined
(in González Dı́az and Nullo, 1980).
Recently, Wenzens (2006a) has indicated the existence
of Late Miocene glacial deposits around Lago Cardiel, an
area that had been considered unglaciated by all previous
researchers (Fig. 1b, Site 44), with ages as old as 10.5 Ma,
and nine glacial advances between 10.5 and 5.4 Ma. These
units would correspond to ice advances of the Lago San
Martı́n lobe of the Patagonian Ice Cap (Fig. 1b, Site 45) or
even by local glaciers at Mount San Lorenzo (Fig. 1b, Site
32). As Wenzens (2006a) has stated, these glacier expansions would have been up to three times larger than their
Pleistocene counterparts. This is quite difficult to explain,
since the larger extent would require very cold and wetter
(at the ice divide) environmental conditions as well as
longer glaciation periods. This assumption does not agree
with the oceanic record, which shows that the Late Miocene
cold events are shorter and much less intense than the
Quaternary glacial periods (Kenneth, 1995; Rabassa et al.,
2005). The existence of these very early, extensive Late
Miocene glaciations is extremely interesting, but intriguing
and further studies are needed to confirm these interpretations and explain this apparently anomalous behavior.
Some of these late Tertiary glacigenic deposits and landforms have been identified well beyond the outermost
boundary of the most extended Pleistocene glaciation. Considering that the Patagonian Ice Sheet is assumed to have
formed only in the Early Pleistocene, when the astronomical
Els AMS
LPCT
00008
22-1-2008
14:06
Page:161
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
forcing cycles were dominated by the eccentricity period of
100 ka (Rabassa et al., 2005), it is difficult to understand
why the ice margin reached such eastern position. It has
been suggested that the ice expanded over a very flat original
surface, with almost no incised drainage, which corresponded to the Late Miocene sedimentary accumulation
plains. Thus, the glaciers would have extended as very
low-gradient, wide ice fans over an almost reliefless surface,
probably eastward-sloping, latest Miocene pediments.
01
02
03
04
05
06
07
08
09
10
161
took place between the Middle and Late Pliocene in
the Buenos Aires, Viedma and Argentino lake regions
(Fig. 1b, Sites 24–26). The first event would have taken
place around 3.5 Ma, during MIS MG6, Gauss normal
polarity, the second one, during the MIS 100, 96, 92 and
88, Matuyama reversed polarity. Tills are found in overand underlying positions of the lava flows dated at
3.20 Ma (Lago Argentino) and 3.45 Ma (Lago Viedma;
Mercer, 1976), respectively, and they are enclosing cold
peaks found at MIS KM4, KM6, M2 and MG2.
11
Glaciations of the Middle Pliocene
12
13
Evidence of Middle–Late Pliocene glaciations can be
found in southern Patagonia as well. In the Lago Viedma
region (Fig. 1b, Site 25), glacigenic deposits interbedded
with basalt flows have been identified at Meseta Chica and
Meseta Desocupada (49 S; Mercer et al., 1975; Mercer,
1976). At Rı́o Cangrejo valley, Meseta Chica, a till bed is
found between two flows K/Ar dated at 3.55 + 0.19 and
3.68 + 0.03 Ma, respectively, and another till unit is overlying a lava flow dated at 3.46 + 0.22 Ma. At Meseta
Desocupada, a till layer occurs in between lava flows
dated at 3.48 + 0.09 and 3.55 + 0.07 Ma.
Wenzens (2000) obtained limiting ages of 3.0 and
2.25 Ma for glacigenic deposits north and east of Lago
Viedma. Sylwan (1989) indicated the presence of till at
Lago Buenos Aires corresponding to MIS 88, during the
Gilbert Geomagnetic Epoch, which is coincident with the
limiting ages proposed by Wenzens (2000) and those of
the basalt flows which underlie till at Cerro Fortaleza,
Lago Argentino (Schellmann, 1998, 1999; Fig. 1b, Site 26).
Mercer (1976) obtained an age of 2.79 + 0.15 Ma for a
lava flow that buries till at Cóndor Cliff, Rı́o Santa Cruz
valley (50 S; Fig. 1b, Site 41). Younger glacigenic deposits
appear over these flows, whereas the materials corresponding to the GPG are located at the base of these ‘‘mesetas’’ or
tablelands. This clearly shows that even as early as the
Middle Pliocene, in some regions the Patagonian glaciers
expanded from the ice caps as far as or close to the extent of
the outlet glaciers of the maximum Pleistocene expansion
(GPG). However, these conditions are probably exclusive
for southernmost Patagonia, since there is yet no conclusive
evidence for a similar extension of the ice cap in Northern
Patagonia, with the exception of Schlieder’s (1989) observations in the Aluminé valley (Fig. 1b, Site 8).
However, at Monte Tronador (41 S; Fig. 1b, Site 12),
volcanics, lahars and pyroclastic flows of the Tronador
Formation (long ago K/Ar dated at 3.2 and 2.0 Ma, though
other much younger ages were obtained as well; Greco,
1975; González Dı́az and Nullo, 1980, p. 1131) appear
in-filling deep valleys, possibly of glacial origin, carrying
striated and faceted, volcanic boulders and cobble-sized
clasts (Rabassa et al., 1986). These units should be redated
with more modern techniques, but it is primarily acceptable
that this part of the northern Patagonian Andes was already
covered by at least local ice during the Middle Pliocene.
The relative chronology of tills and basalt flows has
been compared with the global climatic variability
obtained from the oceanic isotopic sequences (Rabassa
et al., 2005). This analysis indicates that several cold
climatic events and their consequent glacier advances
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Glaciations of the Late Pliocene and Earliest
Pleistocene
Feruglio (1944) described the glacigenic sequences at
Cerro del Fraile (50330 S, Fig. 1b, Site 28), interbedded
between volcanic flows, and considered them as of Pliocene age. These flows were K/Ar dated by Fleck et al.
(1972), Mercer et al. (1975) and Mercer (1976) between
2.08 and 1.03 Ma, during the Matuyama Chron. Mercer
(1976) identified six piedmont glaciations during this
period. Recent studies by Rabassa et al. (1996), Guillou
and Singer (1997), Singer et al. (1999, 2004b) and TonThat et al. (1999) have allowed to redate this sequence by
40
Ar/39Ar incremental-heating techniques and to provide
a precision magnetostratigraphy (Figs 9 and 10). In these
(a)
(b)
Fig. 9. Cerro del Fraile, Santa Cruz Province, Argentina
(Fig. 1b, Site 28). (a) Sequence of interbedded till and
lava flows (Photo by Bradley Singer, 1996); (b) striated
glacial boulder in till (Photo by J. Rabassa, 1996).
AU6
Els AMS
LPCT
00008
162
01
22-1-2008
03
04
Page:162
Trim:210297 mm
Fleck et al. (1972)
Flow Age (Ma) Polarity
05
TS: Integra, India
the Chipanque Moraines would be older than even the
basal glacigenic unit at Cerro del Fraile.
This study
Age (Ma) Polarity
1.05 ± 0.06
1.51 ± 0.11
N
R
(10)
(9)
1.073 ± 0.036
1.61 – 1.43
N
T
F
1.71 ± 0.04
N
(8)
(7)
(6)
1.787 ± 0.085
1.857 ± 0.050
1.922 ± 0.066
R
N
T
(5)
1.994 ± 0.040
R
E
07
Flow
H
G
5
06
Floats: Top/Bottom
Jorge Rabassa
Elevation
1200 m
7
6
02
14:06
The Origin of the Earliest Patagonian Glaciations
4
08
09
D
1.91 ± 0.05
R
(4)
2.130 ± 0.038
R
C
2.11 ± 0.04
N
(3)
2.132 ± 0.031
N
B
2.12 ± 0.07
T
(2)
2.144 ± 0.030
T
A
cobbles
2.05 ± 0.04
R
(1)
2.181 ± 0.097
R
10
3
11
Till
12
13
14
15
16
2
17
18
19
20
21
22
23
1
24
sand
25
cobbles
1020 m
26
Cretaceous sandstone
27
Fig. 10. Stratigraphic sequence at Cerro del Fraile
(Fig. 1b, Site 28). From Singer et al., 2004b. Data from
Fleck et al. (1972), compared with geochronological and
paleomagnetic data in Singer et al., 2004b. A to H,
basaltic flows, according to Fleck et al. (1972); (1) to
(10), lava flows observed by Singer et al., 2004b; 1 to 7,
tills; N, normal polarity, R, reversed, T, transitional.
28
29
30
31
32
33
34
35
36
37
studies, a minimum of seven glaciations have been recognized, and probably a glaciofluvial deposit at the base of
the profile, all of which would have taken place between
2.16 and 1.43 Ma. These glaciations would have developed during MIS 82 to 48 (Matuyama Chron; Ton-That,
1997; Ton-That et al., 1999). Finally, a younger glaciation covered the uppermost lava flow, dated at 1.08 Ma,
thus probably equivalent to the GPG (MIS 30–34).
Strelin (1995) and Strelin et al. (1999) described moraines beyond the position of the GPG (Mercer, 1976) along
the Rı́o Santa Cruz valley, overlying the Cóndor Cliff
basalts (2.66 Ma; Mercer et al., 1975; Fig. 1b, Sites 23,
41), which he considered to be possibly correlated with the
glacial units at Cerro del Fraile. These moraines are older
than a basalt flow dated by 40Ar/39Ar at 0.675 + 0.56 Ma.
No information about the applied technique is given, nor
about the meaning of the very large statistical error of this
date; see, for example, Ton-That et al. (1999) and Singer
et al. (2004a). Likewise, they suggested that the units
known as Chipanque Moraines in Lago Buenos Aires by
Malagnino (1995) could be correlated with the Santa Cruz
valley units. However, Malagnino (1995, p. 80) suggested
instead that the Chipanque Moraines could be older
than 2.3 Ma and younger than 3.5 Ma, following
Mercer’s (1976) chronology. Thus, in this interpretation,
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
It is very important to consider that the definitive glacierization of Western Antarctica took place in the Early
Miocene. The glacierization of eastern Antarctica had
started in the Early Tertiary, when this continent achieved
its present polar position (Kennett, 1995), but the glacierization of Western Antarctica and the Antarctic Peninsula
did not occur until the Drake Passage opened (Fig. 1a).
The Drake Passage is the consequence of the dismembering of both continents due to the continuous
eastward movement of the Scotia plate since the Early
Tertiary. This movement generated the huge bend of
the Fuegian Andean axis from a N–S to an E–W position, the displacement of the southern Georgias Archipelago away from the South American continent and
the formation of a volcanic, oceanic insular arc at the
southern Sandwich Islands, where the Scotia plate
subducts under the Atlantic oceanic plates. The environmental consequence of this new geographic configuration was the installation of the Antarctic
Circumpolar Current in the Early Miocene, perhaps
ca. 23 Ma (Mercer, 1983). This current isolated the
Antarctic Peninsula from the temperate oceanic currents coming from lower latitudes and contributed to
the lowering of the Antarctic oceanic water temperatures. This new environmental scenario allowed the
rapid and definitive cooling of the polar and subpolar
air masses, generating the glacierization of the Antarctic Peninsula (Ciesielski et al., 1982) and, subsequently, of the Fuegian and Patagonian Andes.
In addition to the astronomical forcing (Shackleton,
1995), other causes of climatic deterioration and subsequent
occurrence of Patagonian mountain glaciations should also
be considered. The tectonic processes that slowly elevated
the Patagonian Cordillera and originated the Scotia Arc
(Ramos, 1999a and b) should not be moved aside in this
analysis. The Patagonian Andes would have started its
elevation process, at least partially, in the Late Oligocene
or the Early Miocene (González Bonorino, 1973; Rabassa,
1975). The great pyroclastic eruptions that produced the
tuffs and ignimbrites of the Collón Curá Formation
in northern Patagonia (ca. 15 Ma; Rabassa, 1975) are indicators of such tectonic processes. An incremental-heating
40
Ar/39Ar dating on ignimbritic pumice overlying the
Pilcaniyeu Ignimbritic Member of the Collón Curá Formation (Rabassa, 1975) has provided an age of 10.85 +
0.033 Ma (B. Singer, personal communication; Rabassa
et al., 2005). This date may be interpreted as the age of the
last pyroclastic episodes of the Miocene cycle, which would
be representing the final emplacement of the Patagonian
Andes at elevations comparable to its present position.
The summit accordance line of the northern Patagonian Andes is located today around 2200 m a.s.l., whereas
the regional, permanent snowline is placed at around
2000 m a.s.l., allowing the persistence of many small
cirque glaciers and snow fields, even during the present
Interglacial (Rabassa et al., 1980). It may be assumed
Els AMS
LPCT
00008
22-1-2008
14:06
Page:163
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
that the regional snowline would have descended significatively during all Late Cenozoic cold episodes at least
since the Late Miocene, thus favouring the formation of
larger mountain glaciers, and even perhaps, extending
beyond the mountain piedmont.
01
02
03
04
05
06
07
08
4.3. Quaternary Glaciations in Patagonia
163
Chron, that is, ca. 1.8 Ma. Glacial climatic episodes
became then long enough to allow the formation of a
single, continuous mountain ice sheet that extended for
almost 2500 km, at least between 36 and 56 S, that
covered almost completely the Patagonian Andean ranges
and extended over the piedmont areas to the east (and to
the present submarine platform south of the Rı́o Gallegos;
Fig. 1b, Site 27) and to sea level in the Pacific side.
09
10
During the Early Pleistocene, the Patagonian Ice Sheet
was fully developed, probably for the first time in the Late
Cenozoic, when the orbital eccentricity forcing signal
became dominant (Fig. 11). The lower time boundary of
the Quaternary used in this chapter is the top of the Olduvai normal polarity event of the reversed Matuyama
11
12
13
14
15
Glaciations of the Early Pleistocene
At the base of Monte Tronador (41 S, Fig. 1b, Site 12),
northern Patagonia, Rabassa et al. (1986) and Rabassa
and Clapperton (1990) identified glacigenic deposits
16
17
Fig. 11. Map of Patagonia with the
position and distribution of the
Pleistocene Patagonian Ice Sheet and
relevant tectonic features. From Singer
et al., 2004a.
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
164
22-1-2008
14:06
Page:164
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
Fig. 12. Glacial boulder within a tillite, interbedded in
Early Pleistocene lava flows at Garganta del Diablo,
Monte Tronador, northern Patagonia, Argentina
(Fig. 1b, Site 12). (Photo by J. Rabassa, 1988).
20
21
22
23
24
interbedded with volcanic flows. These rocks were originally K/Ar dated at 1.36 and 1.32 Ma, assigning them an
Early Pleistocene age, previous to the GPG. However, the
volcanic flow overlying both the Garganta del Diablo tillite
and glacial surfaces eroded on the Cretaceous granites has
been redated by 40Ar/39Ar incremental-heating techniques
by B. Singer (personal communication; sample TR-01;
Rabassa et al., 2005; Fig. 12) at 1.021 + 0.102 Ma. Therefore, at least part of these glacigenic deposits could be much
younger and even equivalent to the GPG (Mercer, 1976).
The GPG represents the maximum expansion of the
ice in extra-Andean Patagonia. Its geographical distribution was correctly mapped by Caldenius (1932) and corresponds to his ‘‘Initioglacial’’ event, but considered by
him as an initial phase of the last Pleistocene glaciation,
as stated above. The morainic arcs pertaining to the GPG
are well preserved, though somewhat lesser than the later
sequences. In northern Patagonia, the GPG corresponds
to the ‘‘Pichileufuense’’ (Feruglio, 1950) or Pichileufu
Drift (Flint and Fidalgo, 1964, 1969), or at least to its
outermost expansion. Most likely, the GPG represents
more than one glacial advance and in the type area of
this glacigenic unit, the Rı́o Pichileufu valley east of San
Carlos de Bariloche (41 S; Fig. 1b, Site 16), at least
three clearly defined morainic arcs have been observed.
Flint and Fidalgo (1964) had considered this drift unit as
corresponding to an earlier phase of the LG, following
Caldenius’ model but ignoring Feruglio’s (1950) pioneer
correlations, and only later (Flint and Fidalgo, 1969) they
accepted the possibility that it could correspond to an
earlier glaciation. Much later, Kodama et al. (1985,
1986) and Rabassa et al. (1986, 1990a) defined a preLG age for these deposits, and most likely, an Early–
Middle Pleistocene age, based on 40Ar/39Ar (whole rock)
dating and paleomagnetic studies. Rabassa and Evenson
(1996) suggested that the Pichileufu Drift could be composed of at least the deposits of three different ice
advances which may correspond to one or, perhaps,
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
several glaciations, all of which preceded a fluvial canyon cutting event during the Early Pleistocene (Rabassa
and Clapperton, 1990).
South of San Carlos de Bariloche, the region of Esquel is
located (Fig. 1b, Site 22). This area was studied by Flint and
Fidalgo (1969), where they extended their threefold glacial
model from the Nahuel Huapi area. Caldenius (1932)
described a four moraine sequence, plus several ‘‘postFiniglacial’’ (e.g. the age equivalent to the ‘‘Younger Dryas’’
(YD) moraines of Scandinavia) units inside the mountains.
Miró (1967), González Dı́az (1993a, b) and González Dı́az
and Andrada de Palomera (1995) basically followed
Caldenius’ classical four-moraine system. The longitudinal
valley of El Maitén (42–42300 S; Fig. 1b, Site 20) is
considered as of pre-Andean age (Martı́nez, 2002). This
valley had been glaciated in several episodes by two major
ice lobes, the Epuyén and Cholila valley lobes (Fig. 1b, Site
19). Smaller transversal valleys, crossing the El Maitén
depressions, were occupied by the ice during ‘‘Initioglacial’’
times, reaching its maximum extent at ca. 70400 W. At
Portezuelo de Apichig (Fig. 1b, Site 22), all cited authors
have identified two or more morainic ridges, with abundant
erratic boulders and faceted and striated cobbles, assigned
to the GPG. Further south, González Dı́az (1993b) mapped
a well-preserved moraine belt at Arroyo Pichicó, at
1090 m a.s.l. The same author has also identified another
moraine belt of the same age at Cañadón Blancura, 20 km
farther to the SE. At Portezuelo de Leleque (71430 W;
Fig. 1b, Site 22), González Dı́az (1993b) described two
morainic arcs of ‘‘Initioglacial’’ age, at 700–800 m a.s.l. It is
very important to mention that González Dı́az (1993a, b) and
González Dı́az and Andrada de Palomera (1995) have
proposed a glacifluvial origin for the Blancura Formation
(previously considered as of piedmont origin by Volkheimer,
1963), one of the most important units of the Patagonian
gravels in northern Patagonia. Feruglio (1950) advanced a
similar opinion half a century before.
In the Chilean Lake District, at Lago Llanquihue and
neighboring basins (Fig. 1b, Site 13), Mercer (1976)
described and mapped three drift units older than the
Llanquihue Drift or LG, which he named Rı́o Frı́o, Colegual and Casma drifts. The intensely weathered nature of
the Rı́o Frı́o Drift would suggest a GPG age for this unit
(Mercer, 1976; Clapperton, 1993). Porter (1981) mapped
the drift sequence in the same area, suggesting a new
stratigraphy, composed of the Caracol, Rı́o Llico, Santa
Marı́a and Llanquihue drifts. The drift units were identified in terms of their mappable features, including weathering rate, pedogenetic characteristics and landform
preservation. Caracol, the oldest Drift, occurs along the
bottom of the central valley and also in certain localities
along the eastern slopes of the Cordillera de la Costa
(Clapperton, 1993; Fig. 1a). However, this glaciation
was probably less extensive than the following advance
of the ice, indicated by the Rı́o Llico Drift. The Caracol
Drift is fully weathered and its age is most likely corresponding to the GPG. This unit is not exposed at Isla
Chiloé (Fig. 1a) and probably covered by the younger
drifts (Clapperton, 1993).
A precise, reliable correlation between the Early
Pleistocene glacial events on both sides of the Andes at
this latitude is still lacking, mostly due to the problems of
Els AMS
LPCT
00008
22-1-2008
14:06
Page:165
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
accurate dating of these units. However, a glaciation
model of four major events, the GPG and three younger
episodes, the youngest being the LG of Late Pleistocene
age, seems to be sustainable.
Within the Lago Buenos Aires Basin (46300 S; Fig. 1b,
Site 24), at least 19 terminal moraines, all of them of
Pleistocene age, have been described by Mörner and Sylwan
(1989), Ton-That et al. (1999), Singer et al. (2004a) and
Kaplan et al. (2004, 2005). These units were deposited by
piedmont glaciers advancing eastward from the Patagonian
ice cap during the last 1.2 Myr. 40Ar/39Ar incrementalheating and unspiked K/Ar experiments (Guillou and
Singer, 1997; Singer et al., 2004a) on four basaltic lava
flows interbedded with the moraines provide a chronologic
framework for the entire glacial sequence. The 40Ar/39Ar
isochron ages of three lavas that overlie till 90 km east of
Lago Buenos Aires strongly suggest that the ice cap reached
its greatest eastward extent ca. 1.1 Ma, during the GPG.
At least six moraines were deposited within the 256 kyr
period bracketed by basaltic eruptions at 1016 + 10 and
760 + 14 ka (Singer et al., 2004a; Fig. 13). Six other
younger, more proximal moraines were deposited during a
651 kyr period bracketed by 760 + 14 and 109 + 3 ka
basalt flows.
Recently, Douglass and Bockheim (2006) have studied the relationships between the glacial landforms,
particularly moraine belts, of the Lago Buenos Aires
region with the soils developed on them. These authors
used distinct parameters such as accumulation rates of
organic matter, pedogenetic carbonate and clay, to show
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
165
that they decreased with decreasing age of the moraines.
A lack of changes in soil redness, and preservation of
minerals that should have been weathered in the oldest
soils indicates that chemical weathering is almost absent
in these environments. According to Douglass and
Bockheim (2006), measured dust input explained the
accumulation of both clay and carbonate, and a carbonate
cycling model describing potential sources and calcium
mobility in Patagonia has been presented. These authors
stated that calibration of rates of soil formation would
provide a powerful correlation tool for soils developed on
different Patagonian glacial deposits.
A complementary point of view has been presented
by Gaiero et al. (2004), who stated that fluvial- and windborne materials transferred from Patagonia to the SW
Atlantic show a very homogeneous rare earth element
(REE) signature. The REE composition is compatible
with recent tephra from Volcán Hudson (46 S; Fig. 1b,
Site 35). This would imply a dominance of material
supplied by this source and other similar Andean
volcanoes. Due to the trapping effect of drainage basins,
Patagonian streams deliver to the ocean a suspended load
with a slightly modified Andean signature, showing an
REE composition depleted in heavy REEs. These authors
considered Patagonia a sedimentary source distinguishable from other sources in southern South America.
Quaternary sediments deposited in the Scotia Sea, and
most dust in ice cores of east Antarctica would have REE
compositions very similar to Buenos Aires Province loess
and to Patagonian eolian dust. The REE compositions of
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 13. Map of the Pleistocene glaciations at Lago Buenos Aires, Santa Cruz Province, Argentina (Fig. 1b, Site 24).
From Singer et al., 2004a.
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
166
22-1-2008
14:06
Page:166
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
most sediment cores of the Scotia Sea and Antarctica
would reflect a distal transport of dust with an admixed
composition from two main sources: a major contribution
from Patagonia, and a minor proportion from source
areas containing sediments with a clear upper crustal
signature (e.g. western Argentina) or from the Bolivian
Altiplano. However, the evidence presented by these
authors indicates that Patagonian materials were the
undisputable predominant sediment source to the southern latitudes during the LGM only.
During the GPG, the ice tongues reached the Atlantic
coast in the area north of the Magellan Straits and south
of the Rı́o Gallegos valley (Fig. 1b, Site 27) for the first
time in the Cenozoic, and expanded deeply over the
present submarine platform. It is not clear whether the
ice margin was effectively calving into the Atlantic
Ocean, perhaps as far as 200 km east of the present
coast. The expansion of the ice over the present submarine platform was clearly mapped already by Caldenius
(1932), as shown by his glacial map of Tierra del Fuego
and the Magellan Straits (Fig. 14).
Mercer (1976) estimated the age of the GPG, based
on K/Ar dating of lava flows underlying glacigenic
deposits in different localities south of the Rı́o Gallegos
valley, between 1.47 + 0.1 and 1.17 + 0.05 Ma.
Meglioli (1992) obtained total fusion, whole-rock
40
Ar/39Ar ages of 1.55 + 0.03 Ma at the Bella Vista
Basalt, Rı́o Gallegos valley (Fig. 1b, Site 27), which is
covered by glacial erratics, thus providing a basal limiting age for the GPG. Ton-That et al. (1999) and Singer
et al. (2004a) redated the Bella Vista Basalt by incrementalheating 40Ar/39Ar techniques at 1.168 + 0.007 Ma, considering that the observed discrepancy with Meglioli’s
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Fig. 14. Glacial map of Tierra del Fuego and the
Magellan Straits (Caldenius, 1932).
(1992) date is given by the higher precision of the latter
technique. Likewise, Ton-That et al. (1999) and Singer
et al. (2004a) provided for the first time a reliable upper
limit for the GPG by means of the incremental-heating
40
Ar/39Ar date of 1.016 + 0.005 Ma for the Telken
Basalt, which covers the ‘‘Initioglacial’’ ( = GPG) deposits at Lago Buenos Aires (Fig. 1b, Site 24).
According to the morphological and chronostratigraphic evidence of the till deposits, the Fuegian Andes
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Fig. 15. Glacial map of the Magellan Straits, by Meglioli (1992). This is a portion of the still unpublished map of his
renowned dissertation, showing the distribution of the different Pleistocene moraines. The outermost moraine
corresponds to the GPG (Bella Vista Drift), the two following ones to the latest Early Pleistocene and earliest Middle
Pleistocene (Cabo Vı́rgenes and Punta Delgada drifts, respectively), and the two innermost, to the Late Middle
Pleistocene (Primera Angostura Drift) and the Late Pleistocene (Segunda Angostura Drift).
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
22-1-2008
14:06
Page:167
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
ice sheet would have had a different extent and thickness
in each of the known glacier advances, reaching the
present submarine platform and the Fuegian lowlands to
the north and the Drake Passage waters to the south at
several occasions, receding to the summits and highlands
during the interglacial periods.
The absolute number of glacier advances that took
place in southernmost South America is still a matter of
debate. North of the Magellan Straits at least six major
glacier advances have been described on the basis of
terminal moraines (Meglioli, 1992; Fig. 15), whereas in
Tierra del Fuego the morphological evidence points to two
ice advances in the southern part and five in the north.
Enigmatic, isolated boulders, as well as small till remnants, have been found in the Rı́o Grande city area and the
Rı́o Chico valley (Meglioli, 1992; Coronato et al., 2004b;
Figs 1c and 16) at various elevations along the large
triangular zone between the Bahı́a Inútil–San Sebastián
and Fagnano ice lobes and the ice margins along the
high mountains of western Tierra del Fuego (Fig. 1c).
This area had been considered unglaciated by Nordenskjöld (1899) but implicitly totally covered by ice at the
‘‘Initioglacial’’ stage by Caldenius (1932). These boulders
(of undoubtedly glacial origin, based on their size and
shape) and the surviving till patches were named the Rı́o
Grande Drift by Meglioli (1992), who estimated its age
between 2.05 and 1.86 Ma, by stratigraphic and geomorphological correlation with drifts and radiometric dated
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
167
basalts in southern Patagonia. Therefore, Meglioli (1992)
interpreted these glacigenic remnants as older than the
GPG, of latest Pliocene or earliest Pleistocene age. Though
the issue of full glaciation of the island is still open, these
glacigenic remnants are strong evidence in that sense.
Caldenius (1932) recognized the extension of his aforementioned four glacial events north of the Magellan Straits
but only three on the southern coast. He located the eastern
limit of the two oldest glaciations beyond the coast, onto
the present Atlantic submarine platform. According to his
interpretation, both of these glaciations covered the entire
island. His field mapping was extremely detailed, and quite
correct most of the times, in spite of the serious difficulties
in doing fieldwork, which in some cases even prevented
him of reaching some areas. The Quaternary glaciations of
Tierra del Fuego were very extensive. Large outlet glaciers
of the Darwin Cordillera (2000 m a.s.l.; 55 S–69 W;
Figs 1c and 17) ice cap flowed north and eastward to
reach the present Atlantic submarine platform (Porter
1989; Meglioli et al., 1990; Isla and Schnack, 1995) following large, deep valleys known today as the Magellan
Straits, Bahı́a Inútil–Bahı́a San Sebastián Depression, Lake
Fagnano, Carbajal–Tierra Mayor valley and the Beagle
Channel (Fig. 1c). Several glaciations have been recognized in the northern part of the island (Meglioli et al.,
1990; Meglioli, 1992) and at least two along the Beagle
Channel (Rabassa et al., 1992, 2000).
Meglioli (1992; see also Coronato et al., 2004a) mapped
in great detail a very large area (over 25,000 km2) of
the Magellan Straits and surrounding areas. He identified five or six large glacial events that he gave local
names for each major valley, and which he correlated
with the GPG and subsequent glaciations. The GPG was
named the Bella Vista Drift in the Rı́o Gallegos valley and
Sierra de los Frailes Drift in the straits area and northern
Tierra del Fuego.
A drumlin and megaflute field of GPG or Bella Vista
glaciation (Meglioli, 1992) age has been recently
described by Ercolano et al. (2004), in the Rı́o Gallegos
valley of southernmost Patagonia (52 S; Fig. 1b, Site 27;
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
Fig. 16. Large glacial erratic boulder, originated in the
Darwin Cordillera (Fig. 1), and found today isolated on
top of Tertiary marine sediments, together with small
remnants of till. Estancia Marı́a Behety, 20 km west of
Rı́o Grande, Tierra del Fuego, Argentina. This boulder
corresponds to the elusive ‘‘Rı́o Grande Drift’’, as
defined by Meglioli (1992). (Photo by J. Rabassa, 2004).
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Fig. 17. Landsat image (1996) of Cordillera Darwin,
western Tierra del Fuego, Chile (Fig. 1), showing the
Fuegian Ice Sheet, and large discharge glaciers flowing
in all directions, including the Beagle Channel and the
Magellan Straits.
Els AMS
LPCT
00008
168
22-1-2008
14:06
Page:168
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
and Rı́o Gallegos valley lobes. Its type locality is found in
the marine cliffs between Rı́o Cullen and Cabo Espı́ritu
Santo, along the Atlantic coast, where it can be observed
that the till forms the high plains and mesetas.
The GPG would thus have developed sometime
between 1.168 and 1.016 Ma, during MIS 30–34, and
even maybe MIS 36, most likely including more than
one glacial advance.
01
02
03
04
05
06
07
08
09
10
11
Glaciations of the Latest Early–Middle Pleistocene
12
13
Fig. 18. Drumlins and megaflutes of the Bella Vista Drift,
Early Pleistocene (Meglioli, 1992; Ercolano et al., 2004), in
the Rı́o Gallegos valley, Santa Cruz Province, Argentina
(Fig. 1b, Site 27). The central megaflute is 2.5 km long.
Oblique aerial photograph on a stormy day by Bettina
Ercolano and Elizabeth Mazzoni, 2002.
14
15
16
17
18
19
20
21
Fig. 18). Several tens of streamlined landforms, some of
them several kilometers long that clearly appear even in
satellite images, have been identified in a 30 km long
section. Uncovered since perhaps 1 Ma, these landforms
are beautifully preserved, thanks to the very dry climate
and the lack of surface runoff during most of the Quaternary, showing only the incision of meltwater channel
related to the ice recession during the GPG. Likely, these
features are some of the oldest, well-preserved glacial landforms in the world, outside Antarctica.
The Magellan Strait lobe was the largest and most
impressive glacier that covered this region. It originated
in the Darwin Cordillera and flowed to the north and east
toward the Atlantic Ocean. Several discharge tongues
came out in several directions.
The highest (and oldest) drift in the Magellan Strait
lobe, in northern Tierra del Fuego (Sierra de los Frailes
Glaciation; Meglioli, 1992), extends over the high plains
(100 m a.s.l.). This is a wide flat surface, with poor fluvial
drainage, but which underwent an intense deflation.
Although the superficial morphology does not show
clear glacial landforms in this area, the till, as seen
along the marine cliffs, forms the sedimentary core of
the high plains. On this surface, large volcanic clasts
show a similar weathering degree to those of the corresponding till unit in the northern coast of the Straits. This
drift unit occurs as remnants between the Magellan
Straits and Bahı́a Inútil–Bahı́a San Sebastián Depression
lobes, probably representing a piedmont-type glaciation
that would have covered the southern end of the continent
and a large portion of Isla Grande de Tierra del Fuego.
The Bahı́a Inútil–Bahı́a San Sebastián Depression
lobe, emerging from the main body of the Magellan Straits
Glacier and the northern slope of the Darwin Cordillera,
reached the Atlantic Ocean Platform and the inner portions
of Isla Grande de Tierra del Fuego at various occasions
(Fig. 1c). The oldest tills of this lobe are exposed on top of
the flat and high surfaces that form the Pampa de Beta.
There are no volcanic flows in this area to be dated.
However, the Pampa de Beta Drift is thought to correspond to the GPG, by correlation with the Magellan Straits
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
After the GPG, the deposits corresponding to the following
Patagonian glaciations (‘‘Daniglacial’’ and ‘‘Gotiglacial’’,
according to Caldenius, 1932; or post-GPG 1, 2 and 3, in
the sense of Coronato et al., 2004a and b) are located at
lower elevations in the landscape, and sometimes nested
inside the GPG limits but very far from them.
This circumstance is different to what may be seen in
the Northern Hemisphere Scandinavian and Laurentian
ice sheets, where the younger ice expansions in most
cases reached the outer positions of the older glaciations
and even extended beyond them. These conditions could
be due to (1) a smaller intensity of the Southern Hemisphere cold episodes after the MIS 30–34 or (2) local
phenomena. Concerning the first hypothesis, the Southern Hemisphere oceanic isotopic sequences do not show
significant deviations from their equivalents of the Northern Hemisphere and they suggest similar intensities and
chronology. Therefore, the circumstances may be investigated through phenomena of local nature. The evidence
suggests that episodes of valley deepening took place
over most of the Pleistocene, particularly the Middle
and Late Pleistocene. The most important would have
taken place immediately after the GPG, forcing the later
glaciations to develop a morphology of discharge glaciers
entrenched in their valleys, whereas the dominant glacier
morphology during the GPG would have been of large
piedmont lobes, of great extension but relative reduced
thickness. This characteristic would have been favored
by the preexisting landscape, with little incision of the
piedmont valleys. This event has been named the ‘‘canyon-cutting event’’ by Rabassa and Clapperton (1990)
and Rabassa and Evenson (1996), in comparison with
similar episodes that occurred in the Rocky Mountains.
This valley deepening event may have been caused by
(1) increased erosion related to a larger discharge during
the interglacial periods, (2) increased erosion related to
tectonic ascent of the Patagonian Andes, (3) different
glacier behavior, with large areas of cold ice on the
divides separated by temperate ice in the valleys, or
(4) a combination of some or all of these processes. The
much larger magnitude of the deepening between the
GPG deposits and the later events, compared to that
existing in between the latter, suggests that alternative
(2) would probably be correct. The cited tectonic
uplift would have taken place perhaps between 1.0 and
ca. 0.8–0.7 Ma, since in the next post-GPG the glaciers
were already entrenched (Ton-That et al., 1999). This
event would have possibly contributed even more intensively to the development of ‘‘rain-shadow’’ conditions in
Els AMS
LPCT
00008
22-1-2008
14:06
Page:169
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
extra-Andean Patagonia, but its effective influence in the
extra-glaciated Pampean Region is still unknown.
The glacial event immediately after the GPG is
known as ‘‘Daniglacial’’, according to Caldenius (1932) or
‘‘post-GPG 1’’, in the sense of Coronato et al. (2004a, b).
This unit is characterized by conspicuous and wellpreserved morainic arcs that are located in inner positions
respective to the GPG and entrenched in the valleys
younger than this glaciation. In northern Patagonia, this
unit was complexively named as ‘‘El Cóndor Drift’’ in
the San Carlos de Bariloche type area (Fig. 1b, Site 9) by
Flint and Fidalgo (1964, 1969), including also the ‘‘Gotiglacial’’, but considering it of Late Pleistocene age. Later,
Schlieder (1989), Rabassa et al. (1990a) and Rabassa and
Evenson (1996) proposed the subdivision of the
‘‘El Cóndor Drift’’ in two allostratigraphic units, La Fragua Drift and Anfiteatro Drift, in the type area of the Rı́o
Limay valley (41 S, Fig. 1b, Site 3), or their equivalents,
the San Huberto and Criadero de Zorros drifts, further
north, in the Rı́o Malleo valley (39 S, Fig. 1b, Site 17).
This subdivision was based on detailed mapping in both
valleys, where the aforementioned units occur clearly
separated both in distance and in elevation. The La Fragua
and Anfiteatro drifts appear also along the dirt road east of
the San Carlos de Bariloche Airport (Fig. 1b, Site 9),
where Flint and Fidalgo (1964) defined the ‘‘El Cóndor
Drift’’. Possibly, if these authors had concentrated their
work in the Limay valley, their glaciation model would
have been different, since the obvious drift elevation distribution in that valley is indicative of significant relative
age differences. However, in the Estancia El Cóndor area,
the differentiation of the drift bodies is more difficult
because of ice-contact glaciolacustrine sediments and
several coastlines of proglacial lakes. The La Fragua
Drift has been assigned to Caldenius’ (1932) ‘‘Daniglacial’’
event (Schlieder, 1989; Rabassa and Evenson, 1996;
Rabassa et al., 2005).
In the Esquel region (Fig. 1b, Site 22), the ‘‘Daniglacial’’ moraines are found immediately west of the outermost GPG terminal systems, as entrenched sedimentary
bodies at lower topographical levels. These units have
been named the ‘‘post-GPG 1’’ glaciations by Martı́nez
(2002) and Coronato et al. (2004a). These ridges act
today as local continental water divides, bounding the
Pacific slope basins. At Portezuelo de Apichig, Caldenius
(1932), González Bonorino (1944) and González Dı́az
and Andrada de Palomera (1995) have identified a morainic arc of this age, which is physically related to the
glaciofluvial gravels of the Fita Michi Formation
(Volkheimer, 1963). Thus, the morainic ridges of ‘‘Daniglacial’’ times are clearly linked to the ‘‘Patagonian gravels’’ in northern Patagonia. At Portezuelo de Leleque, at
least three frontal moraines highly degrade by massmovement processes have been mapped behind the
‘‘Initioglacial’’ ridges. Frontal moraines of assumed
‘‘Gotiglacial’’ age (post-GPG 3; Martı́nez, 2002; Coronato et al., 2004a) occur at Portezuelo de Apichig. The
moraines have later been eroded by spillways from glacial lakes.
At the latitude of Lago Epuyén and the heads of Rı́o
Chubut (Fig. 1b, Site 19), the best-preserved morainic
arcs are found. These would correspond to the
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
169
‘‘Gotiglacial’’ (post-GPG 3) and they merge eastward
with glaciofluvial plains and toward the west with large,
varved glaciolacustrine deposits.
In the Lago Buenos Aires region (Fig. 1b, Site 24),
Ton-That (1997), Ton-That et al. (1999) and Singer et al.
(2004a) obtained limiting ages for the ‘‘Daniglacial’’ drift,
by means of incremental-heating 40Ar/39Ar dating of two
lava flows associated to glacial deposits. The alreadymentioned Telken Basalt is the first of them
(1.016 + 0.005 Ma), which covers the ‘‘Initioglacial’’
deposits or GPG, and predate the ‘‘Daniglacial’’ or ‘‘postGPG 1’’ deposits. Moreover, the Telken Basalt presents a
transitional paleomagnetic polarity, which corresponds to
the upper portion of the Jaramillo Subchron. The second is
the Arroyo Page Basalt, dated at 0.760 + 0.007 Ma, of
normal magnetic polarity, which covers the recessional
outwash deposits of the ‘‘Daniglacial’’ stage (see Fig. 13).
Thus, the ‘‘post-GPG 1’’ or ‘‘Daniglacial’’ event would
have taken place possibly around MIS 18–20, immediately
before the Early–Middle Pleistocene, indicated by the
Matuyama–Brunhes paleomagnetic transition, dated at
0.78 Ma (Singer and Pringle, 1996).
In the Chilean Lake District (Fig. 1b, Site 13), Porter
(1981) considered that at least one of the glaciations
could have been developed in this period. The Rı́o
Llico Drift is clearly older than the Santa Marı́a Drift,
based on weathering criteria and other field evidence.
Since the Santa Marı́a Drift is pre-Late Pleistocene in
age (Porter, 1981; Clapperton, 1993), a Daniglacial age
for the Rı́o Llico Drift is acceptable.
On Isla Chiloé, south of Puerto Montt and southwest of
the lake district (42 S; Fig. 1a), Heusser and Flint (1977)
recognized a three-glaciation sequence of which the oldest
unit, the Fuerte San Antonio Drift, has been correlated
with the Rı́o Llico Drift (Porter, 1981) and it is considered
to be of early Middle Pleistocene age, overlying a lava
flow dated at 0.75 Ma (K/Ar) (Clapperton, 1993).
In the Magellan Straits area, Meglioli (1992;
Coronato et al., 2004a) mapped two glacial units that
can be correlated with Caldenius’ (1932) ‘‘Daniglacial’’
event: the Cabo Vı́rgenes and the Punta Delgada drifts. In
northern Tierra del Fuego, these units are known as the
Rı́o Cullen and Sierra de San Sebastián drifts, whereas
only one unit, the Glencross Drift, has been mapped
within the Rı́o Gallegos valley (Fig. 1b, Site 27).
These glacial advances expanded within deeper valleys, following the ‘‘Canyon cutting event’’. Above
their highest reach, the GPG deposits are forming
almost relief lacking high plains. The oldest of these
advances (the Cabo Vı́rgenes Glaciation; Meglioli,
1992) is represented by well-defined moraine arcs,
though with subdued, planar summits (100 m a.s.l.),
which reach the cape where the drift is defined. The
moraines are represented on both sides of the straits;
the terminal position is not visible, though it is inferred
that it may be submerged on the present Atlantic platform in the eastern entrance of the Magellan Straits, or
that its moraines have been eroded by the fluvioglacial
streams of later glaciations.
An inner moraine belt is developed on both margins
of the Magellan Straits up to Bahı́a Posesión (northern
margin) and Punta Catalina (southern margin, Fig. 1a, c).
Els AMS
LPCT
00008
170
22-1-2008
14:06
Page:170
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
These moraines have been interpreted as a second advance
of the ice lobe (the Punta Delgada Glaciation), which is
separated from the Cabo Vı́rgenes Drift, due to differences
in morphology, soil development, periglacial features and
weathering rinds of the clasts incorporated in the till. Both
the Cabo Vı́rgenes and the Punta Delgada drifts, and their
Fuegian equivalents, are considered to be of Gotiglacial
age and probably pertaining to the latest Matuyama and
the earliest Brunhes paleomagnetic chrons.
In the Bahı́a Inútil–Bahı́a San Sebastián depression
(Fig. 1c), a post-GPG advance is evident on both its
margins, represented by the Rı́o Cullen moraines, with
SW–NE orientation, forming a wide, ample relief of
planar summits and continuous landforms. On the southern margin, the Rı́o Cullen Drift covers the slopes and
high plains of the Sierras de Carmen Sylva (350 m a.s.l.),
in northern Tierra del Fuego, extending toward the Atlantic Ocean in the shape of a flat moraine, with elongated
ridges formed by glaciofluvial deposits and an extensive
erratic boulder field at Punta Sinaı́ (Fig. 1c; Coronato
et al., 1999; Coronato et al., 2004b). Recent cosmogenic
nuclide measurements and paleomagnetic studies have
indicated a Middle Pleistocene age for these deposits
(Kaplan et al., 2007; Walther et al., 2007; Fig. 19). On
the basis of submarine morphology investigations (Isla
and Schnack, 1995) the terminal position of the moraine
arc is located 40 km into the sea.
Toward the center of the cited depression and at both
of its margins, the San Sebastián moraines are located,
forming the core of the mountain ranges of this name on
the northern margin, up to 60 m a.s.l. (Fig. 20). Its wellpreserved, kettle-hole topography represents disintegration
ice stages along the highest plains. The type locality is
Cabo Nombre, on the Atlantic coast (Fig. 1c), where a
gray, compact till, with abundant fragments of fossil
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Fig. 20. Giant erratic boulder on top of the San
Sebastián Moraine, early Middle Pleistocene, Los
Chorrillos, Bahı́a San Sebastián, Tierra del Fuego,
Argentina (Fig. 1c). Calvin J. Heusser, the author and
Nat Rutter for scale. (Photo by A. Meglioli, 1988).
shells, wood and coal derived from the preexisting sedimentary rocks, has been identified. The frontal position of
this moraine would be located below present sea level, at
approximately 20 km into the sea (Isla and Schnack 1995).
Finally, based on paleomagnetic and absolute dating,
the Daniglacial event would have developed between
1.01 and 0.76 Ma, most of this unit being of latest
Matuyama age, perhaps during MIS 21–25, perhaps
even MIS 19 (Shackleton, 1995). These drifts are
probably equivalent to the younger units of the
‘‘pre-Illinoian’’ glacial deposits of Midwestern United
States (Stiff and Hansel, 2004).
However, recent paleomagnetic work on the till units
at Bahı́a San Sebastián have indicated a Brunhes age for
all sampled deposits (Ana Walther, personal communication), showing that these deposits have an age 0.78 Ma
(Singer and Pringle, 1996). These new data suggest that at
least part of those stratigraphic units in Tierra del Fuego
and the Magellan Straits corresponding to Caldenius’
‘‘Daniglacial’’ stage are clearly Mid-Pleistocene in age.
42
43
Glaciations of the Middle Pleistocene
44
45
46
47
48
49
50
51
52
53
Fig. 19. Erratic boulder field on top of the Rı́o Cullen
Moraine, latest Early–earliest Middle Pleistocene, Punta
Sinaı́, Bahı́a San Sebastián, Tierra del Fuego, Argentina
(Fig. 1c). The boulders are composed of one single
lithology, granodiorites coming from the Darwin
Cordillera, most likely a rock avalanche on top of the
glacier. Some of the boulders have been exposed at the
moraine surface at least for more than 200,000 years
(Kaplan et al., 2007). (Photo by J. Rabassa, 2004).
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
The most important glacial event of the end of the Middle
Pleistocene is the ‘‘Gotiglacial’’ period (Caldenius,
1932), though in more southern localities like Lagos
Buenos Aires, Viedma and Argentino (Fig. 1b, Sites
24–26), in the Skyrring and Otway Sounds, in the Magellan Straits region and Tierra del Fuego (Fig. 1b, Sites 38,
39), a previous glaciation defined as post-GPG 2 has been
recognized (Coronato et al., 2004a, b).
The ‘‘Gotiglacial’’ event corresponds to the younger
portion of the ‘‘El Cóndor Drift’’ (Flint and Fidalgo,
1964), to the Anfiteatro Drift, of the Upper Rı́o Limay
valley (Rabassa and Evenson, 1996; Fig. 1b, Site 3;
Fig. 21) and to the Criadero de Zorros Drift, of the Rı́o
Malleo valley (Fig. 1b, Site 17; Rabassa et al., 1990a), in
Neuquén, northern Patagonia.
The ‘‘Gotiglacial’’ moraines or their stratigraphic
equivalents appear in all studied localities as very
Els AMS
LPCT
00008
22-1-2008
14:06
Page:171
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Fig. 21. Stratified drift, glaciotectonically deformed,
Anfiteatro Moraine of Gotiglacial age (= Late Illinoian
age), Rı́o Limay valley, Neuquén Province, Argentina
(Fig. 1b, Site 3). (Photo by J. Rabassa, 1988).
24
25
26
27
28
29
well-preserved morainic arcs, located on valley sides
above the altitudinal range of the LG and at several tens
of kilometers downvalley from its terminal moraines. Its
state of preservation is excellent, which clearly explains
why Caldenius (1932) and Flint and Fidalgo (1964) had
mistaken them for deposits of a phase of the LG. The
assignation of these deposits to this glaciation was possible, thanks to geomorphological studies and radiometric dating of associated volcanic rocks.
At the Rı́o Malleo valley (39 S, Fig. 1b, Site 17), the
Pino Santo Basandesite was originally dated by K/Ar at
0.207 Ma (Rabassa et al., 1990a). This flow is infilling a
glacial valley excavated in post-Criadero de Zorros Drift
times. This basandesite was redated later by B. Singer
(Sample PSA-01; personal communication; Rabassa
et al., 2005) at 0.089 + 0.004 Ma by incremental-heating
40
Ar/39Ar techniques. In both cases, these dates confirm the
pre-Late Pleistocene age of the Criadero de Zorros Drift
(= ‘‘Gotiglacial’’). In the Rı́o Limay valley (Fig. 1b, Site
3), the Anfiteatro Drift is correlated with the Criadero de
Zorros Drift (Rabassa and Evenson, 1996; Rabassa, 1999)
and, thus, to a pre-LG event, based on their surficial morphology and their respective altitudinal positions with
respect to the LG deposits. However, a TL date performed
on glaciofluvial sands incorporated in the Anfiteatro Moraine (Fig. 21) yielded an age of 0.065 Ma (Amos, 1998),
thus implying that the Anfiteatro Drift would have formed
during MIS 4 (Early Late Pleistocene). However, this TL
date should be considered as a ‘‘minimum age’’, unless
very local, unknown conditions have operated in the area,
since in no other site in Patagonia MIS 4 morainic arcs are
found so far downslope from and altitudinally above the
LG moraines (Kaplan et al., 2004, 2005).
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
171
In the Chilean Lake District (Fig. 1b, Site 13), Porter
(1981) has identified a large glacial event, well beyond
the boundaries of the LG, represented by the Santa Maria
Drift. This unit is located around 7–14 km east of the
Early Pleistocene glacial deposits and more than 20–30 km
west of the LG Llanquihue moraines forming arcuate
ridges interpreted as moraines by Laugenie and Mercer
(1973). This drift has been 14C dated at 57.8 ka, which
should be considered as a minimum age due to contamination with modern rootlets (Clapperton, 1993), and its
degree of weathering, relative to older and younger moraines (Porter, 1981).
In the Lago Buenos Aires region (47 S, Fig. 1b, Site
24), a lava flow of normal magnetic polarity, which
erupted from the Cerro Volcán, postdates the post-GPG
2 and post-GPG 3 (‘‘Gotiglacial’’) deposits and predates
those of the LG (Coronato et al., 2004a). This flow was
dated by whole-rock K/Ar by Mercer (1976) at
0.177 + 0.056 Ma. Ton-That et al. (1999) obtained a
date by 40Ar/39Ar plateau age of 0.123 + 0.005 Ma and
an unspiked K/Ar age of 0.128 + 0.002 Ma was presented by Guillou and Singer (1997) and Singer et al.
(2004a). These dates were later confirmed by cosmogenic isotopes (3He) exposure dates from pyroxene concentrates, which provided an average age of
0.128 + 0.003 Ma (Ackert et al., 1998; Singer et al.,
1998, 2004a; Fig. 13), as a weighed mean of four sites
and two locations. These ages confirm also that the 3He
production rates at 47 S are constant for the last 100 kyr.
Later, in situ cosmogenic surface exposure ages of
boulders in the Moreno moraines (Kaplan et al., 2005;
Fig. 22) together with the 109 ka 40Ar/39Ar age of Cerro
Volcán (Singer et al., 2004a) imply that the moraines
deposited during the penultimate local glaciation correspond to MIS 6. These ages have been challenged by
Wenzens (2006b), who claimed that cosmogenic dates
are useless in these environments and that the dated Cerro
Volcán flow is in fact redeposited basalt, suggesting
instead MIS 2 ages for these units based on 14C dating.
However, Kaplan et al. (2006) have rejected these objections, particularly those concerning the primary nature of
the volcanic flows and confirmed their glacial chronology for the area.
In the Magellan Straits area, Porter (1989) identified
different drift units based on weathering criteria. Moraines older than the LG were described at Primera
Angostura and marine shells included there were dated
at >47 ka, confirming a pre-LG age for these deposits.
The significantly higher degree of weathering of these
moraines suggested a pre-LG age as well. Meglioli
(1992) defined local glacial units corresponding to the
Middle Pleistocene in the different ice lobes. In the Rı́o
Gallegos valley (Fig. 1b, Site 27), the Rı́o Turbio Drift
was defined, whereas in the Straits area the prominent
Primera Angostura moraines have been assigned to this
period. In northern Tierra del Fuego, Meglioli (1992)
assigned the moraines in the middle portion of the
Bahı́a Inútil–Bahı́a San Sebastián depression (Fig. 1c)
to the Lagunas Secas Drift, at an elevation of
180 m a.s.l., of Middle Pleistocene age. The Lagunas
Secas Drift is composed of deeply dissected moraine
arcs, with small E–W elongated lakes, probably ancient
Els AMS
LPCT
00008
172
22-1-2008
14:06
Page:172
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Deseado I
01
02
03
Moreno II
Moreno I
Moreno III
04
06
07
08
350
300
Fenix moraines
23–16 ka
250
09
10
200
oldest boulder ages
11
12
Ages
no erosion
analytical uncertainties
13
14
10
Be
15
26
AI
16
3
150
Cerro
Volcán
Exposure age (ka)
Lago
Buenos
Aires
200 m a.s.l.
05
100
50
He
17
18
Samples
25 27 30 31 37 13 62 66 134
West/Andes
19
65 66 68 110111
46 48 50 51 52
68 73
East /Atlantic
(a)
20
21
Moreno II
Moreno I
22
Moreno III
23
700
24
300
26
250
27
28
200
29
30
Ages
erosion 1.4 mm/kyr
propagated uncertainties
31
32
33
34
10
Be
26
AI
3
150
Cerro
Volcán
Exposure age (ka)
500
25
100
50
He
35
36
Samples
37
25 27 30 31 37 13 62 66 134
65 66 68 110111
46 48 50 51 52
68 73
(b)
38
39
Fig. 22. Cosmogenic age of the Moreno Moraines, Lago Buenos Aires, Santa Cruz Province, Argentina (Kaplan et al.,
2005; Fig. 1b, Sites 24, 42). The Moreno moraines represent two or more glaciations during the late Middle Pleistocene,
including the Illinoian and perhaps, part of the pre-Illinoian glacial events.
40
41
42
43
44
outwash channels, strongly eroded and deepened by deflation. Both Porter (1989) and Meglioli (1992) have
accepted an MIS 6 age for these moraines, but other
previous glacial events (i.e. MIS 8–12) may be present as
well. Clapperton (1993) suggested that the moraines at the
Straits of Magellan are most likely of composite origin and
thus presenting a large range of glacial events, not only
equivalent to MIS 6, but throughout the entire Pleistocene.
In central Tierra del Fuego, the Lago Fagnano lobe
was built by many different glaciers merging to form a
large, outlet valley glacier in the present Seno Almirantazgo, a branch of the Magellan Straits (Fig. 1c). The lake
basin is in fact a tectonic depression crossed by the firstorder Magellan fault, the boundary between the South
American and Scotia plates. An ice thickness of more
than 1500 m favored its eastward spreading, with additional ice supply from local glaciers at Sierra de Beauvoir
and Sierra Alvear, on both sides of Lago Fagnano.
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Caldenius (1932), Auer (1956) and Meglioli (1992) suggested that the eastern limit of the ice lies between the
Irigoyen and Noguera ranges, east of Lago Fagnano, or
even along the Atlantic coast. However, Caldenius
(1932) had indicated in his map the possibility that the
entire island had been covered by the ‘‘Initioglacial’’
(= GPG) glaciers, with their terminal moraines lying
somewhere on the submarine platform. Thus, Caldenius
(1932) is clearly referring to post-GPG events. Between
the Atlantic shore and the eastern end of the lake, a
moraine belt is found, in which Laguna del Pescado
(20 km east of Lago Fagnano) and a number of peat
bogs are situated. This belt was mapped by Caldenius
(1932) as the outermost extent of the ice in this area,
corresponding to his ‘‘Gotiglacial’’ glaciation.
In the Lago Fagnano lobe, the moraines at the eastern
end of the lake are thought to correspond to glacier
oscillations during the Middle Pleistocene. Meglioli
Els AMS
LPCT
00008
22-1-2008
14:06
Page:173
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
(1992) identified two drift units predating the LG: (i) the
Rı́o Valdez Drift, along the southern coast of Lago Fagnano, believed to be of Illionian/Riss or pre-Illinoian/Riss
age; and (ii) the Lago Chepelmut Drift, beyond the northern lake coast, which is referred to Late Illinoian glaciation. These units are covered by LG deposits along the
margins of the lake and several kilometers beyond its
eastern end. A proglacial deltaic sequence assigned to
the Rı́o Valdez Drift develops along the eastern lake
margin, next to Hosterı́a Kaikén, at the easternmost end
of Lago Fagnano (Bujalesky et al., 1997; Fig. 23). The
gravel and lacustrine sequence overlies basal till and
other glacial deposits and underlies till and other glacigenic units related to the frontal moraines at the eastern
margin of Lago Fagnano. Two peat beds, dated at 39,000
14
C yr BP and >53,000 14C yr BP (Bujalesky et al.,
1997; Rabassa et al., 2000), interbedded in the upper
lacustrine levels, suggest that the delta was formed by
deglaciation processes during an Early Wisconsinan/
Würm or pre-Wisconsinan/Würm interstadial, when climate was colder and drier than today. Recent findings
(November 2005) of thin organic layers in between till
units much farther west along the lake cliff have confirmed pre-LGM radiocarbon ages for these units (unpublished data). The pollen content of these layers lacks
arboreal (Nothofagus spp.) pollen, confirming an impoverished tundra environment associated to glacial conditions (J.F. Ponce, personal communication). Thus, the
glacigenic materials outcropping along the southern margin of the lake were formed either during a very early
phase of the LG or, most likely, during the final phase of
the penultimate glaciation (MIS 6, Late Illinoian/Riss).
The Beagle Channel (Fig. 1c) is a drowned glacial
valley, formerly occupied by a large outlet glacier, the
former ‘‘Beagle Glacier’’, from the Darwin Cordillera.
This valley was repeatedly glaciated, at least in two
major episodes. Caldenius (1932) described glacial
deposits in the Beagle Channel and on the Nueva, Lennox and Navarino islands (Fig. 1c). These are the oldest
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
173
known glacial deposits in the southern Fuegian Andes:
the so-called Lennox Glaciation. Evidence from previous
glaciations was certainly eroded by the ‘‘Beagle Glacier’’
during successive events.
The oldest recognizable glaciation has been named
the Sloggett Glaciation, which is considered of Illinoian/
Riss age, MIS 6 and older (Rabassa et al., 2004). During
this event, the ice occupied the entire channel basin, as
far away as Bahı́a Sloggett (Fig. 1c), depositing the Punta
Jesse and Punta Argentina moraines (Rabassa et al.,
2004), located east of the LG moraines or Moat Glaciation (see below). A thick sequence of glaciofluvial gravels along the bay head would represent ice melting
episodes of perhaps both pre-Moat and Moat age. Inner
moraines, closer to the mountain front, would represent
the maximum development of a local glaciation of Moat
age, with local cirque and valley glaciers, independent
from the Fuegian mountain ice field. Fieldwork has
established the existence of a drumlin field beyond the
Moat moraines (David Serrat, pers. comm.). Whether
these drumlins were formed during MIS 6 (corresponding
to the Slogget Glaciation) or 4 (earlier phase of the LG) is
still a task of future research.
Based on the presented evidence, it is possible to
confirm a pre-LG age for the ‘‘Gotiglacial’’ period and
its equivalent units (post-GPG 3 and post-GPG 2;
Coronato et al., 2004a). It is most likely that the glacial
deposits included in this unit would have been formed
during MIS 6, but they could also have been originated in
other previous Middle Pleistocene cold periods, such as
those between MIS 8 and 16. Thus, the ‘‘Gotiglacial’’
event are only partially coeval to the ‘‘Illinoian Stage’’ of
Midwestern United States or the Riss Glaciation of the
European Alps, since it includes this stage but most likely
extends beyond MIS 10, perhaps comprising some of the
so-called pre-Illinoian deposits in the United States.
Glaciations of the Late Pleistocene
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
Fig. 23. Glacigenic sediments at the cliffs of Lago
Fagnano, Hosterı́a Kaikén (Fig. 1c), Tierra del Fuego.
Glacial delta beds overlying basal till. Lacustrine and
peaty deposits overlying the sequence have infinite
radiocarbon ages, suggesting that these deposits may
correspond to a glacial advance during MIS 4, or more
likely, MIS 6. (Photo by J. Rabassa, 2004).
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
The glacigenic deposits of the LG in Patagonia and Tierra
del Fuego are those that were formed after the Last Interglacial, that is, MIS 5e, 125 ka (Panhke et al., 2003). The
LGM was reached during the last major glacial event of
the Late Pleistocene, during MIS 2, after a relatively
warmer period identified with MIS 3. The age of the
glacigenic deposits of the LG may be estimated starting
perhaps at a maximum of 85 ka, since the process of
formation of the Patagonian Andes ice sheet was undoubtedly slow and took at least 30 ka after the maximum of the
Last Interglacial. A maximum concentration of d18O has
been identified in Atlantic marine records as well as a
minimum of dD has been recognized at the Vostok ice
core, both around 70–75 ka BP (Panhke et al., 2003),
suggesting the most probable age of the largest temperature depression in the Southern Hemisphere during MIS 4.
Therefore, the ice expansion could have taken place only
at an advanced stage of MIS 4. In most available marine
and ice isotopic records, MIS 4 temperature depression
was significant, but not as large as that of MIS 2.
The LG was named as ‘‘Finiglacial’’ by Caldenius
(1932), and as Nahuel Huapi Drift by Flint and Fidalgo
AU7
AU8
Els AMS
LPCT
00008
174
22-1-2008
14:06
Page:174
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
(1964). This denomination has been preserved by later
authors. The LG in the Chilean Lake District is known as
the Llanquihue Glaciation (Mercer, 1976; Porter, 1981;
Clapperton, 1993).
Clapperton (1993) proposed to extend the name
of ‘‘Llanquihue Glaciation’’ to the LG in the whole
South American continent, with its type area in the
Lago Llanquihue, Chilean Lake District (40–41 S, Fig.
1b, Site 13; Lowell et al., 1995), being represented by the
Nahuel Huapi Drift on the eastern slope of the Andes.
Clapperton (2000) summarized the knowledge about the
LG in the southern Andes, in the most significant areas,
such as the Chilean Lake District, the Patagonian ice
fields, the Magellan Straits and the Beagle Channel. This
author recognized a minimum of five glacial advances
during the LG in the southern Andes, around 30, 27,
22.5, 15 and 12–9.3 14C ka BP.
The LG deposits form moraines of extremely wellpreserved morphology, very fresh appearance, abrupt slopes
and abundant erratic boulders on their surface. The more
reliable chronological dates for the LG are coming precisely
from the Lago Llanquihue area. There, successive studies
by Mercer (1976), Porter (1981), Lowell et al. (1995) and
Denton et al. (1999a, b) have provided an adjusted chronology based on radiocarbon dates. According to these
authors, there were ice expansions during the MIS 4 and
recession during the MIS 3 (Laugenie, 1984; see Rabassa
and Clapperton, 1990; Clapperton, 1993). Based on an
extremely detailed radiocarbon chronology, Lowell et al.
(1995) have identified later readvances during MIS 2,
which peaked at 13,900–14,890, 21,000, 23,060, 26,940,
29,600 and more than 33,500 yrs BP. Revised chronology
of these areas, including Isla Chiloé (Fig. 1a), by Denton
et al. (1999a, b), indicated that full-glacial or similar environmental conditions were maintained between 29,400 and
14,550 14C yr BP, with major glacial advances at 29,400,
26,670, 22,295–22,570 and 14,550–14,805 14C yr BP.
Cooling events, suggested by pollen data from Isla Chiloé,
would have taken place at 44,520–47,110, 32,105–35,762,
24,895–26,019, 21,430–22,774 and 13,040–15,200 14C yr
BP. The maximum expansion of the ice in the northern part
of the studied area occurred at 22,295–22,570 14C yr BP,
whereas in the southern portion it took place at
14,805–14,869 14C yr BP (Denton et al., 1999b). This outstanding reconstruction of glacial events in a large, piedmont area, showing variable glacier behavior in different
parts of the ice front, is very important to evaluate and
understand apparent discrepancies in moraine chronology
over extended areas. The facts exposed in the cited papers
should be carefully taken into consideration when discussing chronology of terminal moraines, in relationship with
global climate episodes.
The external positions of MIS 4 ice were generally
reached and even surpassed by MIS 2 readvances. There
are perhaps exceptions at certain areas of Lago Llanquihue, where the outermost moraine, Llanquihue I (Porter,
1981) was formed more than 39,000 14C yr BP, and in
Lago Ranco (north of Lago Llanquihue), where it was
deposited more than 40,000 14C yr BP (Laugenie and
Mercer, 1973). Mercer (1983) suggested that the Llanquihue I outer moraines would be ca. 73,000 yrs old, and
correlated them with MIS 4.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Lowell et al. (1995) and Denton et al. (1999a, b)
concluded that the glaciers of the Chilean Lake District
finally collapsed ca. 14,000 14C yr BP and suggested that
the ice advances in this region were coeval with ice-rafting
pulses of the North Atlantic Ocean, and that the last
termination was suddenly and simultaneously initiated in
both hemispheres before the modern termohaline circulation was restarted. These authors concluded that interhemispheric coupling implied a global atmospheric signal
forcing rather than regional climatic changes.
The extent of the LG on the Argentinian slope of the
Andes at this latitude, the San Carlos de Bariloche–Lago
Nahuel Huapi area (Fig. 1b, Site 9; Fig. 24), has been
studied by Feruglio (1950), Flint and Fidalgo (1964),
González Bonorino (1973), Rabassa (1975), Schlieder
(1989) and Rabassa and Evenson (1996), among many
others. The LG is represented by the Bariloche moraines,
wrapping around the eastern edge of the lake. Equivalent
moraines in similar positions can be found near most of
lakes in the region. At least two well-defined moraines of
this age (Nahuel Huapi I and II) have been identified,
each of them around 1 km wide, though so far no absolute
chronology is available (Rabassa and Clapperton, 1990).
These two moraines are separated by a depression filled
by outwash, tephra and eolian deposits. Radiocarbon
dates on these moraines are lacking due to the absence
of organic matter in the tills, probably because of the
extreme aridity of the area during the maximum expansion of the ice. Contrary to what happened on the Chilean
side, where the ice advanced into the northern Patagonian
Nothofagus forest, on the Argentinian side the forest was
displaced eastward and northward or just supressed,
trapped in between the ice front and the 500 mm-yr
isohyeth on the dry Patagonian tablelands. A few exceptions exist, as in the Rı́o Malleo valley (Fig. 1b, Site 17),
where Rabassa et al. (1990a) found organic layers on top
of the Criadero de Zorros Drift (Penultimate Glaciation)
and covered by the LG outwash dated at more than
30 ka BP. Schlieder (1989) and Rabassa et al. (1990a)
presented K/Ar data on volcanic flows in the Rı́o Malleo
and neighboring valleys, which provided limiting ages
for the LG, which is younger than 0.126 + 0.019 Ma. As
cited above, Rabassa et al. (2005) quoted 40Ar/39Ar
Fig. 24. Lago Nahuel Huapi, northern Patagonia
(Fig. 1b, Site 9), a glacial piedmont lake. (Photo by
J. Rabassa, 1979).
Els AMS
LPCT
00008
22-1-2008
14:06
Page:175
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
LGM in Lago Buenos Aires Area
02
Moraine age (ka)1 Age (ka)2
175
03
Mean ±1σ
Mean ±1σ
05
Fénix I
15.6 1.1
15.3 1.1
06
FénixII
18.7 1.0
18.8 1.1
07
Fénix III
20.7 1.3
20.4 1.5
08
Fénix V
23.0 1.2
22.7 1.4
04
09
10
11
12
13
14
Fig. 25. Clastic dykes in Late Pleistocene
glaciolacustrine sediments, San Martı́n de los Andes
(van der Meer et al., 1992; Fig. 1b, Site 18). (Photo by
J. Rabassa, 1988).
15
16
17
18
Fig. 26. Cosmogenic ages of the LGM moraine systems,
Lago Buenos Aires area, Santa Cruz, Argentina (Fig. 1b,
Site 24). From Kaplan et al., 2004. 1Means based on
boulder 10Be/ 26Al ages that include propagation of all
uncertainties except for production rate. 2Means based
on boulder 10Be/ 26Al ages that include propagation of all
uncertainties including production rate. For explanation
see Kaplan et al., 2004.
19
20
redating of the Pino Santo Andesite at Rı́o Malleo
(B. Singer, personal communication; 0.089 + 0.004
Ma) providing a closer upper age for the LG in the
area. Ongoing cosmogenic dating research may for the
first time provide absolute dates for the northern Patagonian ice advances on the eastern side of the Andes
(A. Hein and O. Martı́nez, personal communication,
2006). Glacial deposits of the LG have been studied by
van der Meer et al. (1992) in San Martı́n de los Andes, in
the northern Patagonian Andes (Fig. 1b, Site 18) from a
sedimentological and glaciotectonic point of view (Fig. 25).
In Volcán Copahue, northern Neuquén Province (37 S;
Fig. 1b, Site 11), González Dı́az (2003) has recognized
only one major glaciation on the eastern slopes of this
active volcano. Previous works had identified two glaciations, but the older one is reinterpreted as a Pleistocene
giant slide from the volcano slopes. The confirmed glacial
event is considered of Late Pleistocene age, followed by a
very rapid recession.
The LG in the area south of San Carlos de Bariloche
(Fig. 1b, Site 9) was studied by Caldenius (1932) who
recognized extensive ‘‘Finiglacial’’ and ‘‘post-Finiglacial’’
moraines, the latter of assumed post-LGM age, i.e.
Late Glacial. Flint and Fidalgo (1969) extended their
respective four- and threefold glaciation model southward,
being also unable to obtain an absolute chronology of their
Nahuel Huapi Drift. Similar conditions were encountered
by González Dı́az and Andrada de Palomera (1995) and
Martı́nez (2002). Miró (1967) mapped two morainic arc of
‘‘Finiglacial’’ (LG) age in the Epuyén valley (43 S;
Fig. 1b, Site 19). Lapido et al. (1990) described the Mallı́n
Grande Drift at 43 300 S, forming two well-preserved
morainic arcs with their corresponding glaciofluvial
plains, and adjacent glaciolacustrine deposits, assigning it
to the LG. Martı́nez (2002) proposed to consider only the
inner of the Mallı́n Grande moraines as of LG age
(Coronato et al., 2004a).
In the Lago Buenos Aires region (Fig. 1b, Site 24),
recent work by Kaplan et al. (2004) has confirmed the
age of the LGM by means of cosmogenic isotope dating,
allowing the differentiation of five glacial episodes, of
which the outermost corresponds to the LGM. The
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
respective ages, expressed in calendar years, extend
between 25 ka for the outermost Fenix V Moraine and
16 ka for the innermost Fenix I Moraine (Fig. 26). An
AMS radiocarbon age of 15.3 + 0.3 ka BP in post-LGM
glaciolacustrine deposits confirms the validity of these
exposure ages and provides an upper limiting age for the
LGM in this region. On top of these glaciolacustrine
deposits, the Menucos Moraine corresponds to a postLGM (early Late Glacial) advance, dated at 13.8 ka by
cosmogenic isotopes. The whole set of moraines is
younger than the Cerro Volcán Basalt flow
(0.109 + 0.003 Ma; Singer et al., 2004a). Surface exposure dating of boulders on these moraines, combined with
the 14C age of overlying varved lacustrine sediment,
indicates deposition during the LGM (23–16 ka).
Although Antarctic dust records signal an important
Patagonian glaciation as their most likely source at
around 60–40 ka, moraines corresponding to MIS 4 are
not preserved at Lago Buenos Aires, or elsewhere in
southern Patagonia. Most likely, the MIS 4 moraines
were overrun and obliterated by the younger (MIS 2)
ice advance (Singer et al., 2004a). The LGM ages for
the Fenix moraines have been recently discussed by
Wenzens (2006b) and Kaplan et al. (2006).
Wenzens (2000, 2002) suggested that the present
separation of the northern and southern Patagonian ice
sheets is not just a consequence of Holocene melting
away of the Pleistocene Ice Sheet, but a feature that
was already established during the LG. The depression
between both ice sheets is related to a tectonic depression, which already in the Pleistocene oriented ice drainage toward the Pacific Ocean. The eastern margin of the
ice at this latitude (4745–48150 S) would then be the
result of moraine accumulation by local valley glaciers,
isolated from the major ice cap. The expansion of the
LGM glaciers south of this latitude was much reduced
when compared with the Northern Patagonian Ice Sheet
eastern margin. This has been interpreted as a result of
the northward displacement of the Pacific precipitation
belt during glacial times (Wenzens, 2000).
The Patagonian glaciations are progressively smaller
during successive glacial advances after the GPG. These
circumstances were explained by Rabassa and
Els AMS
LPCT
00008
176
22-1-2008
14:06
Page:176
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Clapperton (1990) as the effect of tectonic uplift during
the Early Pleistocene after the GPG, which induced the
downcutting of fluvial valleys (the ‘‘canyon-cutting
event’’), modifying the original pattern of piedmont
lobes into subsequent development of discharge glaciers
nested in deep valleys during later glaciations. However,
the total volume of ice would have remained almost
constant. Alternatively, Singer et al. (2004a) hypothesized that tectonically driven uplift of the Patagonian
Andes, which began in the Pliocene, yet continued into
the Quaternary, in part due to subduction of the Chile rise
spreading center during the past 2 Myr, maximized the
ice accumulation area and ice extent by 1.1 Ma. Subsequent deep glacial erosion has reduced the accumulation
area, resulting in less extensive glaciers over time.
Marden (1994) has discussed the volume and provenance of the glacigenic deposits in Torres del Paine (51 S,
73 W; Fig. 1b, Site 30) and other areas of the southernmost Andes, concluding that the sediment budget of
the last ice sheet was low, with very little supraglacial
debris input and limited older drift reworking, because
most glaciers advanced over drift-free terrain, the deposits of earlier ice sheets being confined to areas beyond
the extent of the Last Glaciation. For this author, glacial
erosion in the southern Andes seemed to be decreasing
with successive glaciations. Alternatively, in the opinion
of the present author, once the upper portions of the
Tertiary weathered surface (a subtropical planation surface) had been denudated, the lower, unweathered materials were not removed easily, thus modifying the total
sediment budget. One of the interesting features of the
glacigenic deposits of the southernmost part of this
region is that gold particles, supposedly coming from
the Darwin Cordillera, at the core of the ice sheet, and
which were exploited intensively in Tierra del Fuego
during the early twentieth century, occur only in the
Early and Middle Pleistocene drifts, being almost absent
in the youngest drifts. This fact may be related to total
erosion of the original gold veins in the accumulation
area of the ice sheet or a radical change in rock
accesibility.
The innermost moraine arc in the Magellan Straits
region (Fig. 1a) is located at Segunda Angostura, a narrow pass in the Straits, representing the youngest glaciation. These moraines present little erosion, angular
ridges, nonfilled depressions, and abundant, slightly
weathered metamorphic clasts. Soils have very poor
development. The regional glaciation model proposed
by Meglioli (1992) includes the Segunda Angostura
Drift as the local equivalent of the LG, composed of
several moraines, in tightly packed belts. The Bahı́a
Inútil Drift is the local equivalent of the LG along the
depression of this name. The heads of the bay and its
margins are surrounded by these moraines, composed of
a clayey–silty till, with scarce clast content, glaciolacustrine structures and abundant, large erratic boulders,
aligned over the surface. This moraine is in fact a landform complex, representing different glacial advances.
Clapperton (1989) described an LG drumlin field at
Cabeza de Mar, along the northern shore of the Magellan
Straits (Fig. 1c), in between the two older moraine ridges
belonging to this glaciation.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Clapperton et al. (1995) mapped inner moraine arcs
(in relation to the Segunda Angostura moraines) between
Isla Santa Isabel and Penı́nsula Juan Mazı́a, central
Magellan Strait (Fig. 1c). The five mapped moraine
arcs have been interpreted as glacial advances that took
place during the Last Glacial cycle and Late Glacial
events. A similar model has been suggested by these
authors for the Bahı́a Inútil ice lobe.
McCulloch and Davies (2001) discussed climatic
events in the Magellan Straits, based on pollen and diatom sequences at Puerto del Hambre, south of the city of
Punta Arenas (Fig. 1b, Site 31). They recognized that the
ice receded from the site sometime before 14,470 14C yr
BP (17,330 cal. yr) and that a significant glacier readvance took place between ca. 12,000 and 10,300 14C yr
BP. After this date, a very dry period started, which they
associated with a high rate of forest fires. A different
approach had been presented by Heusser (2003), who
considered the charcoal accumulation as an indication
of human arrival at the area. Note that the original basal
date at this site of 16,590 14C yr BP (Porter et al., 1984)
had been recalculated to 14,455 + 155 14C yr BP, due to
lignite contamination (Heusser et al., 2000; McCulloch
and Davies, 2001).
Sugden et al. (2005) presented extensive information
about the paleoclimatic and paleoenvironmental evolution in the Magellan Straits area during the Late
Glacial–Holocene transition. These authors have suggested that there is a ‘‘blend’’ of Northern Hemisphere
(e.g. North Atlantic Ocean) and Southern Hemisphere
(e.g. Antarctic) climatic signals during this period, such
as ice advances at LGM times (ca. 25–23 ka) and again
at 17.5 ka (both calendar years). They have also recognized a readvance of the ice during the ‘‘Antarctic Cold
Reversal’’ (ACR), ca. 15.3–12.2 ka, with the beginning
of the deglaciation in the middle of ‘‘YD’’ times. Sugden et al. (2005) estimated that these conditions implied
that during the Last Glacial–interglacial transition the
regional climate was determined by a strong Antarctic
signal. They concluded that during deglaciation, the
conditions are more related to oceanographic changes,
such as thermohaline circulation, than to astronomical
forcing.
A careful geomorphological mapping of the Strait of
Magellan and neighboring regions has been attempted by
Bentley et al. (2005). These authors have stated that the
LGM moraines and other landforms can be certainly
separated from those of the older glaciations, on the
basis of geomorphological features, mostly weathering
and drainage development. Likewise, it was possibly to
separate different ice margins during LGM times, based
on discontinuous moraine belts and meltwater channels
that run along their margins. These geomorphological
units have been considered as a very important support
to fully understand the radiocarbon chronology of
the area.
The chronology of the LG in the Magellan Straits
has been presented in great detail by McCulloch et al.
(2005). Several moraine belts, associated with individual glacial advances, have been recognized. The age
of the outermost advance, named as ‘‘A’’, has not been
clearly established. It could be related to a pre-LG
AU9
Els AMS
LPCT
00008
22-1-2008
14:06
Page:177
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
advance (older than 90 ka, based on amino acid data) and
synchronous with the Moreno moraines of the Lago Buenos Aires region (Kaplan et al., 2004) of Late Illinoian/
Riss age. The following stage B corresponds to the LGM
in the area, with ages of ca. 25,200–23,100 cal. yr. Ice
advanced again in stage C (sometime before ca. 21,700–
20,300 cal. yr) and in stage D (before ca. 17,500 cal. yr).
Finally, the ice readvanced again in between ca. 15,507–
14,348 and 12,587–11,773 cal. yr (12,638 and 10,314 14C
yr BP; see also McCulloch et al., 2005). This later
advance is considered to be in phase with the ACR, as
identified in the Vostok ice core record, though it also
overlapped with the onset of the YD period of the Northern Hemisphere. The beginning of rapid warming
and final retreat of the Magellan glaciers took place
sometime before 10,315 14C yr BP (11,770–12,580 cal. yr;
McCulloch and Davies, 2001), which seems to be coincident
with the coolest portion of the YD event. These findings
suggested to McCulloch et al. (2005) that there would be
a clear antiphase behavior between the two hemispheres
during the Late Glacial–Holocene transition.
Benn and Clapperton (2000a) studied the glacial sediments and landforms preserved in the Strait of Magellan
area. The available record showed repeated advances of
outlet glaciers of the Patagonian Ice Field during and
following the LGM (25,000–14,000 14C yr BP). The
ice-marginal landform assemblages are composed of
thrust moraine complexes, kame and kettle topography
and lateral meltwater channels. When analyzed together
with other forms of paleoenvironmental evidence, the
landform complex showed that, during the LGM and
Late Glacial time, permafrost occurred near sea level in
southernmost South America, indicating that mean
annual temperatures were ca. 7–8C lower than at present, somewhat lower than those reconstructed by current
glacier–climatic models. In comparison with precipitation–temperature relations for modern glaciers, precipitation levels would have been lower than today.
Precipitation during glacials would have been lower,
forced by precipitation shadow conditions induced by
the Patagonian Ice Field, as well as an equatorward
migration of the average position of westerly cyclonic
centers.
The significant role of neotectonics in the development of local conditions and disturbances in the geological and geomorphological record has been discussed by
Bentley and McCulloch (2005), particularly in reference
to the classical site of Puerto del Hambre, Magellan
Straits. Late Pleistocene and Holocene movements
along regional faults have affected the sedimentary accumulation and generated drainage diversion, affecting glacial and sea level reconstructions. Several annomalies of
the Puerto del Hambre record can be explained by postglacial neotectonic activity.
Along the eastern margin of Lago Fagnano (Fig. 1c),
Caldenius (1932) mapped ‘‘Finiglacial’’ moraines wrapping around the lake. Meglioli (1992) defined the Lago
Cami Drift as represented by the moraines at the easternmost end of the lake. Further studies are under way in
order to establish the latest glacial stades and glaciolacustrine sequences of the Lago Fagnano Basin, which
extend toward the Atlantic coast along the valleys of
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
177
the San Pablo, Lainez and Irigoyen rivers (Fig. 1c;
Coronato et al., 2005).
Although precise 14C dating is still lacking for the
LGM in Argentinian Tierra del Fuego, the most extensive
expansion of the ice in the eastern Beagle Channel, Tierra
del Fuego, was probably attained between 18 and 20
14
C ka BP, but ice recession from its maximum position
had already started before 14.7 14C kyr BP (Heusser and AU10
Rabassa, 1987; Rabassa et al., 1990b). The Moat Glaciation is represented by a complex system of terminal
moraines at Punta Moat (Fig. 1c). These deposits
and landforms have been correlated to Meglioli’s
(1992) Segunda Angostura and Bahı́a Inútil drifts
(Wisconsinan/Würm Glaciation; Rabassa et al., 1990b).
The position and extent of the ice field during the LGM
has been reconstructed from various lines of evidence
(Coronato et al., 1999) and it is presented in Fig. 27.
Coronato et al. (2004b) defined the Moat Glaciation
as the maximum expansion of the ice in the Beagle
Channel during the Late Pleistocene. Unfortunately,
only minimum 14C ages at the base of peat bogs grown
on top of the moraine have been obtained so far, which
are clearly younger than the assumed ages for the LGM,
and even younger than the basal date at the Harberton
peat bog, located 50 km to the west (Fig. 1c). Further
work is needed to attain a precise, absolute chronology of
the LGM in the Beagle Channel.
At least five, still undated moraine arcs have been
recognized for the LGM, with very fresh morphology,
extending between sea level and 150–200 m a.s.l. A striking feature is the development of a drumlin field on Isla
Gable (Fig. 1c and Fig. 28; Rabassa et al., 1990c).
Drumlins on Isla Gable are part of a larger field that
extends along the Beagle Channel from Estancia Harberton to Bahı́a Brown, and Puerto Williams (Chile). Caldenius (1932) and Kranck (1932) misinterpreted these
landforms as terminal moraines, but Halle (1910) had
already suggested that these landforms could be drumlins
or drumlinoid features. Sedimentary structures reveal that
these landforms would have been formed during the final
phases of the Moat Glaciation. No absolute dating has yet
been obtained for the LGM in this area. A minimum
radiocarbon age of 14,640 + 260 yrs BP for the glacier
retreat from the Punta Moat moraines is given by a basal
14
C date at the Puerto Harberton peat bog (Heusser
1989a, b; Rabassa et al., 1990c; Heusser, 2003; Fig. 29a, b).
The lateral complexes that extend to Estancia Moat,
100–150 m a.s.l., are considered to correspond to the LGM
(Fig. 30). These moraines appear again on Isla Picton and then
on Isla Navarino (Chile; Fig. 1c). At the same time, the upper
surface of the Beagle Glacier at Ushuaia (110 km West
of Punta Moat, Fig. 1c) reached over 1200 m a.s.l., as shown
by glacially eroded surfaces and the occurrence of erratics
inside the major cirques.
According to abundant and relevant evidence, the LG
in Patagonia and Tierra del Fuego is equivalent to the
Wisconsin or Würm glaciations of the Northern Hemisphere, spanning over MIS 4, 3 and 2. Evidence for a
significant expansion of the ice during MIS 4 is available
probably only in the Chilean Lake District and it has been
named as the Llanquihue 1 event. The LGM is repre- AU11
sented by the Llanquihue 2 moraines in Chile and the
Els AMS
LPCT
00008
178
22-1-2008
14:06
Page:178
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
71° O
GLACIOFLUVIAL PLAINS
02
Skyring
03
65° O
N
04
05
ay
w
Ot
ATLANTIC
OCEAN
Bru
07
MAGELLAN
STRAITS
nsw
ick
53° S
08
til
09
ia
ah
B
10
200
06
STEPPE
inu
TUNDRA
11
12
FOREST REFUGE
13
14
15
DARWIN CORDILLERA Fggogno
16
17
Beagle
18
PACIFIC OCEAN
200
19
20
21
22
0
23
50
100 km
CAPE HORN
24
25
26
Fig. 27. Paleogeomorphological and paleoecological map of Tierra del Fuego during the LGM (from Coronato et al.,
1999).
27
28
29
30
Late Glacial Expansions of the Ice
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
AU12
50
51
52
53
54
55
Fig. 28. Last Glaciation drumlin field at Estancia
Harberton, Beagle Channel, Tierra del Fuego,
Argentina (Rabassa et al., 1990; Fig. 1c). This drumlin
is seen from its up-ice end, looking downslope, in a
drowned portion of the drumlin field. Note the Middle
Holocene marine terrace around the drumlin base,
slightly above present sea level, and the wave cut
erosional features on both sides of the drumlin. (Photo
by J. Rabassa, 2004).
56
57
Nahuel Huapi Drift in northern Patagonia, and the Fenix
moraines in the Lago Buenos Aires Basin. The LGM was
attained around 25 cal. ka and ended around 15 cal. ka,
probably corresponding to the Heinrich 2 and 1 events of
the North Atlantic Ocean, respectively.
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
The Patagonian glaciers reached their maximum expansion around 23 ka (calendar years), but several readvances took place until the definitive recession started
around 18–17 ka, based upon basal radiocarbon ages in
peat bogs and cosmogenic dates on recessional moraines
(Kaplan et al., 2004), though other smaller advances
occurred during the Late Glacial. The Late Glacial period
conventionally extends between 15 and 10 14C ka BP, but
ice fluctuations may have started before the older
boundary.
Caldenius (1932) was the first to clearly identify
moraine systems younger than the LGM. He mapped
these units along the bottom of the glacial valleys, in an
intermediate position between the Finiglacial (= LGM)
moraines and the present glacier margins or, instead, the
source cirques. He labeled them ‘‘Post-Finiglacial moraines’’, implying also a timely concept. Most of these
moraines have been found to have Llate Glacial ages.
Porter (1981) described a recessional phase of the ice
in the Lago Llanquihue lobe (Fig. 1b, Site 13), which he
named the ‘‘Llanquihue III’’ event, indicating that there
were no defined moraines assigned to this phase, but a
general ice-disintegration terrain complex, due to stagnant ice, around between 14 and 12.2 14C ka BP.
Mercer (1976) did not support the idea of Late Glacial
advances of the Patagonian Andes. He concluded that the
warming trend initiated around 13 14C ka BP had continued without interruption until Holocene climates were
established. Clapperton (1983) challenged this point of
view, following Caldenius (1932) mapping, and Rabassa
Els AMS
LPCT
00008
22-1-2008
14:06
Page:179
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
179
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
(a)
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
(b)
45
Fig. 29. (a) Harberton Bog, Beagle Channel, Argentinian Tierra del Fuego (Fig. 1c; photo by J. Rabassa, 2004);
(b) absolute pollen rain data. Note the basal age of 14,640 – 260 14C yr BP. From Heusser, 2003.
46
47
48
49
(1983) proposed also that some of the inner moraines of
Lago Nahuel Huapi (Fig. 1b, Site 9) could be of Late
Glacial age, because they were younger than peat basins
with basal ages of ca. 14 14C ka BP, but located far
downslope from the Neoglacial moraines in the same
valley.
Glasser et al. (2004) presented evidence for Late Glacial glacier fluctuations of the Patagonian ice fields. These
authors considered that glaciers still covered large areas of
Patagonia at approximately 14,600 14C yr BP, but uniform
and rapid warming took place after 13,000 14C yr BP.
There has been no agreement about evidence for climate
fluctuations equivalent to those of the Northern Hemisphere
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
YD cooling event (the YD Chronozone), dated to 11,000–
10,000 14C yr BP (12,700–11,500 cal. yr).
Singer et al. (2004a) and Kaplan et al. (2004) have
identified a significant advance of the Lago Buenos Aires
ice lobe (Fig. 1b, Site 24), cosmogenic isotope dated at
ca. 14.4 + 0.9 ka, which they have called the Menucos
moraine, when the ice was overriding its own glaciolacustrine deposits. No other ice expansions have been
recorded here until the early Holocene.
Hajdas et al. (2003) have reported high-resolution
AMS 14C chronologies from the San Carlos de Bariloche
and Chilean Lake District areas (Fig. 1b, Sites 9, 13) that
suggest the development of a cool episode between
Els AMS
LPCT
00008
180
22-1-2008
14:06
Page:180
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
02
03
04
05
06
07
08
09
10
11
12
13
14
Fig. 30. LGM moraines at Punta Moat, Beagle Channel,
Argentina (Fig. 1c). (Photo by J. Rabassa, 1989).
15
16
17
18
11,400 and 10,200 14C yr BP, which they named the
‘‘Huelmo/Mascardi Cold Reversal’’, that would have preceded the onset of the Northern Hemisphere YD cold
event by at least 550 calendar years. However, these
authors estimated that both events occurred during a
radiocarbon-age plateau at ca. 10,200 14C yr BP. Thus,
the Huelmo/Mascardi Cold Reversal and the YD would
have been a couple of short-term cool-warm oscillations
that immediately preceded the onset of the latter in the
North Atlantic region. These observations partially agree
with the discussion by Sugden et al. (2005) about the
ACR, an Antarctic climatic signal affecting southern
Patagonia during Late Glacial times.
Bennett et al. (2000) had denied the existence of a YD
cooling event in southern Chile, based on chronological,
sedimentological and paleoecological records from sediments of small lakes in the coastal zone, which is controlled by a heavily oceanic climate. Thus, these authors
have suggested that there was little or no cooling in the
southern Pacific surface waters, and therefore, indicating
that the YD cooling in the North Atlantic Ocean was a
regional, rather than global, phenomenon. However, it
should be noted that the climate of the studied region is
very different from the rest of Patagonia. In this area, the
available moisture brought from the ocean onto the continent would have probably been constant, regardless of
temperature changes, thus not affecting the distribution
of local species. Perhaps plants and insects do not react to
1–2C changes, whereas glaciers actually do so to ELA
modifications at the same scale. It sounds very extreme to
extend paleoenvironmental conclusions to all of Patagonia, based on findings of a rather unique area.
Though working on a global scale, Blunier and Brook
(2001) have found a close relationship between similar
events in both hemispheres. They studied the methane
and isotopic content in Greenland and West Antarctic ice
cores, confirming that the onset of seven major millennial-scale warming events in Antarctica preceded the
onset of equivalent periods in Greenland by 1500–3000
yrs. In general, Antarctic temperatures increased gradually, while Greenland temperatures were decreasing or
constant, and the termination of Antarctic warming was
apparently coincident with the onset of rapid warming in
Greenland. This pattern provides further evidence for the
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
operation of a ‘‘bipolar see-saw’’ in air temperatures.
However, an oceanic teleconnection between the hemispheres on millennial timescales can be proposed, thus
linking the precedent ACR with the subsequent YD over
such a delay.
Ariztegui et al. (1997) stated that several highresolution continental records have been reported
recently in sites in South America, but the extent to
which climatic variations were synchronous between
both hemispheres during the Late Glacial–Holocene transition, and the causes of the observed climatic changes
have not been solved yet. According to these authors, east
of the Andes, the middle and high latitudes of South
America warmed uniformly and rapidly from 13,000
14
C yr BP, with no indication of subsequent climate
fluctuations, equivalent, for example, to the YD cooling.
They presented a multiproxy continuous record, 14C
dated by accelerated mass spectroscopy, from proglacial
Lago Mascardi (Fig. 1b, Site 15), which indicates that
unstable climatic conditions, comparable to those
described from records obtained in the Northern Hemisphere, dominated the Late Glacial–Holocene transition
in Argentina at this latitude. They suggested that a significant advance of the Monte Tronador local ice cap
(Fig. 1b, Site 12), which feeds Lago Mascardi through
the Upper Rı́o Manso, occurred, however, during the YD
Chronozone. These circumstances suggested a climatic
history that reflected a global, rather than a regional,
forcing mechanism. These authors indicated that the
Lago Mascardi record provides strong support for the
hypothesis that ocean–atmosphere interaction, rather
than global ocean circulation alone, led interhemispheric
climate teleconnections during the last termination.
McCulloch et al. (2000) noted the uncertainty about
the interhemispheric timing of climatic changes during
the Last Glacial–interglacial transition. They discussed
various hypotheses, according to different lines of evidence, which suggest either that the Northern Hemisphere climatic changes were leading the Southern
Hemisphere ones, and vice versa, or alternatively that
both hemispheres acted in synchrony. The location of
southern South America is considered appropriate to
test the various alternatives using both glacial and
paleoecological evidence. These authors estimated that,
from varied sources of evidence, there was a sudden rise
in temperature that initiated deglaciation simultaneously
over more than 16 of latitude at 14,600–14,300 14C yr
BP (17,500–17,150 cal. yr). There was also a second
warming episode in the Chilean Lake District at
13,000–12,700 14C yr BP (15,650–15,350 cal. yr), when
temperatures almost achieved modern values. A third
major warming step occurred at ca. 10,000 14C yr BP
(11,400 cal. yr), reaching Holocene temperature levels.
Following the initial warming, there was a lagged
response in precipitation as the westerlies, after a delay
of ca. 1.6 kyr, migrated from their northern glacial location to their present latitude, which took place ca. 12,300
14
C yr BP (14,300 cal. yr). According to these authors,
the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation
change and in glacier behavior. A large, 80 km glacier
advance in the Strait of Magellan at 12,700–10,300
Els AMS
LPCT
00008
22-1-2008
14:06
Page:181
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
14
C yr BP (15,350–12,250 cal. yr), a period that includes
both the ACR and the earlier part of the YD, was influenced by the southward return of the westerlies. The
delay in the migration of the westerlies would be perhaps
coincident with the Heinrich 1 iceberg event in the North
Atlantic. Thus, the suppressed global thermohaline circulation at that time may have also affected sea-surface
temperatures in the South Pacific, modifying the position
of the westerlies, which returned to their present southerly latitude only after oceanic conditions achieved their
present interglacial mode.
Marden (1997) presented evidence of two Late Glacial advances of the South Patagonian Ice Field at Torres
del Paine (51 S, 73 W; Fig. 1b, Site 30), Chile, which
challenge the concept raised by others that climate in
southernmost South America was characterized by uninterrupted warming after LGM termination. These
advances are marked by moraines and other ice-marginal
deposits, 18–20 km and 10–16 km from the modern
limits of two outlet glaciers, whereas older full glacial
limits are indicated by other sets of moraines ca. 50 km
from the modern glaciers. Pumice clasts included in the
glacial deposits are related to an eruption of Volcán
Reclus (Fig. 1b, Site 34) at ca. 11,880 14C yr BP, which
provided a close limiting age for the older Late Glacial
event, whereas the younger advance occurred during the
interval 11,880–9180 14C yr BP. This author supported
the idea that deglaciation occurred slowly in the studied
area because initial warming was accompanied by
increased moisture as precipitation belts migrated southward. As the climate cooled, the outlet glaciers advanced.
The temperature depression was estimated to have been
not more than 2C below current values, since Late
Glacial moraines at some local glaciers lie within 200 m
of the modern ice margins. This idea of twofold, late
glacial expansions had been previously supported by
palynological evidence (e.g. Heusser, 1987; Heusser
and Rabassa, 1987; Clapperton, 1993; Heusser, 1987,
1993, 2003).
Fogwill and Kubik (2005) have presented preliminary
cosmogenic 10Be data from a former ice limit in Torres
del Paine. The offered data indicate a stillstand or a
readvance of Patagonian glaciers culminating at around
12–15 ka with a mean age of 13.2 + 0.8 ka. The glacier
extended some 40 km beyond the present ice margin and
was within 15 km of the presumed LGM boundary in this
area. This glacier stage is interpreted as partially coincident with the ACR (14.5–12.9 ka). According to these
authors, the data implied that glaciers at these latitudes
were out of phase with those in the Northern Hemisphere,
but instead, followed an Antarctic climatic signal during
Late Glacial times. The Puerto Banderas moraine at Lago
Argentino (Fig. 1b, Site 26) was mapped by Caldenius
(1932) as one of his ‘‘Post-Finiglacial’’ moraines, and
described by Mercer (1976). Strelin and Malagnino
(2000) proposed a Late Glacial age for a system of
three moraine belts, with a maximum age of 15.5 + 2.4
cal. yr. Recently, Strelin and Denton (2005) have suggested a new chronology of these units, following the
previous scheme of using radiocarbon ages of organic
materials found at the marginal moraines. Becker et al.
(2005) discussed the problem of the ACR and YD
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
181
problem in relation to this unit. They have mapped and
dated the Puerto Banderas I and II moraines, and 36Cl and
10
Be dated these moraines with an average age of
11.2 + 05 ka from 18 samples. Mercer (1976) had previously obtained a radiocarbon age of 11.7 + 0.3 ka BP.
Becker et al. (2005) concluded that the Puerto Bandera
Moraine is younger than previously thought, and it is not
related to the termination of the LGM, neither deposited
during the ACR. This ice advance would be consistent
with the expansion of the South Patagonian Ice Field
during, or shortly following, the YD period. Thus, these
authors have stated that the proposal by Sugden et al.
(2005) that the ACR is more prominent in southernmost
Patagonia may be premature. Thus, not all of South
America south of the Chilean Lake District seemed to
be in phase with the Antarctic climate, and as the polar
front and westerlies migrate, the boundary between
‘‘northern’’ and ‘‘Antarctic’’ response may be latitudinally displaced as well.
Mercer (1976) found no evidence around the Patagonian ice fields that glaciers had advanced during the Late
Glacial interval at 12–10 14C ka BP. But because peat
older than 11 14C ka BP lies beneath Neoglacial moraines
in some places, Mercer concluded that since the interval
of deglaciation at ca. 13 14C ka BP, Patagonian glaciers
had not been any more extensive than they are now until
ca. 5000 14C yr BP. Consequently, Mercer (1976) suggested that the Holocene most probably began in southern South America at around 13 14C ka BP and that the
late glacial cooling known as the Younger Dryas in the
Northern Hemisphere had been restricted to north west
Europe.
This opinion was supported by studies of fossil beetles in the Chilean lake region by Hoganson and Ashworth (1992) and by pollen studies in Patagonia east of
the Andes by Markgraf (1991, 1993). These authors also
concluded that the so-called Hypsithermal warming trend
had begun at about 13 14C ka BP and was not followed or
interrupted by any significant cooling. These views are
quite the reverse of those determined from palynological
studies by Calvin Heusser who, in a number of articles
(Heusser, 1974, 1984, 1987; Heusser and Streeter, 1980;
Heusser et al., 1981; Heusser and Rabassa, 1987), had
argued strongly that significant climatic cooling occurred
during not only the last 5 kyr, but also at 11–10 14C ka
BP. The high precipitation and low temperatures estimated by Heusser and Streeter (1980) for the Late Glacial
interval, if valid, should have caused glaciers in the
region to advance.
Clapperton (1993) has argued, however, that in areas
where the Andes are low and presently ice-free, as along
much of the crest east of the Chilean Lake District, the
Late Glacial temperature depression may have been
inadequate to have caused glaciers to form again. He
has also suggested (Clapperton, 1983) that if there are
no Late Glacial moraines around the Patagonian ice
fields, it is because this area had become almost icefree by 13 14C ka BP. Late Glacial cooling might have
initiated the regrowth of glaciers, but these were
restricted to the ranges now buried by the (Neoglacial)
ice field systems. Thus, any Late Glacial moraines that
were deposited lie beneath the present ice cover.
Els AMS
LPCT
00008
182
22-1-2008
14:06
Page:182
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Alternatively, John Mercer may have been wrong in his
observation that Late Glacial moraines do not exist
beyond the limits of those he dated to be part of the
Neoglacial interval.
It is particularly crucial to understand what happened
around the Patagonian ice fields during this interval
because evidence of late glacial advances has been
found in other parts of the southern Andes. Also, in the
San Carlos de Bariloche area, several moraines have been
observed inside the limits of the LGM (Nahuel Huapi
moraines). As they appear well down-valley from those
of the Neoglacial interval in the Rı́o Manso valley, it is
possible that they formed during the Late Glacial interval. They were mapped by Caldenius (1932) as ‘‘PostFiniglacial’’ moraines. Those observed by Rabassa
(1983) at Lago Moreno, Puerto Blest and Divisoria de
Aguas, near San Carlos de Bariloche (Fig. 1b, Site 9), are
worthy of more detailed study as candidates for Late
Glacial limits in this region. They are believed to be
younger than ca. 14 14C ka BP, the age of basal peat in
a bog lying between these moraines and Lago Nahuel
Huapi. Moraines east of the South Patagonian Ice Field
younger than those of the LGM were mapped by Caldenius (1932) and Feruglio (1950). Particularly striking are
those at Punta Bandera, Punta Ciervo and Marı́a Antonia
along the southern shore of Lago Argentino (Fig. 1b, Site
26). They are situated at distances of 22, 24 and 50 km
beyond the present outlet glaciers. These distances suggest that the moraines are more likely to represent limits
of a significant glacial stadial at ca. 15–1414C ka BP.
Along the Beagle Channel, several glacial advances
or stabilization periods took place during Late Glacial
times (Rabassa et al., 1992, 2000). A first ice retreat
phase probably took place before 14.7 14C ka BP. A
model of a calving glacier front, in either the adjacent
sea or a proglacial lake, has been favored. A 1–2 kyr long
stabilization phase could have occurred when the ice
front reached the Isla Gable rise (Fig. 1c). This is suggested by the basal 14C age of the Caleta Róbalo peat
bog (near Puerto Williams, Isla Navarino, Chile, Fig. 1c;
12,700 + 90 yrs BP), a minimum age for ice retreat from
Isla Gable. During the initial recession period, the glacier
thickness decreased at Ushuaia by a minimum of 550 m.
Then, the main Beagle Glacier receded from the cirques,
allowing their glaciers to expand downslope. Two large,
extensive lateral moraines have been mapped around
Ushuaia and named the Pista de Ski and Ushuaia moraines. Radiocarbon dating of basal peat at 12,060 + 60 yrs
BP at Pista de Ski Moraine (300 m a.s.l.) suggested that
this retreat phase probably peaked ca. 12 ka 14C yr BP,
when a relative maximum of arboreal pollen is reached
around 11,780 + 110 14C yr BP, at Puerto Harberton bog
(Fig. 1c; Rabassa et al., 1990b).
Morphological evidence of stabilization occurs also
between Punta Segunda (35 km West of Isla Gable) and
Arroyo Fernández (Fig. 1c), building up a four-stage
frontal moraine complex that extends into the Beagle
Channel, below present sea level. These moraines
develop from 100 m a.s.l. at the mountain sides, in
a discontinuous shape, as till pockets preserved
against erosional bedrock remnants or as low moraines
(<75 m a.s.l.) in the city of Ushuaia. Notwithstanding, the
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
basal ages of the break point (80 m a.s.l.; 12,430 + 80
C yr BP) and San Salvador (10 m a.s.l.; 12,100 + 50
14
C yr BP) peat bogs in Ushuaia show that the ice would
have already disappeared from these sites allowing the
formation of lacustrine environments (Heusser, 1998).
The similarity of the peat bog basal ages between 300
and 10 m a.s.l. in Ushuaia suggested that the ice recession
from Isla Gable to Ushuaia had taken place during a short
period. Although the pollen profiles show evidence of
cooling between 11 and 10 ka and subsequent vegetation
changes (McCulloch et al., 1997), perhaps the climatic
conditions had been not harsh enough so as to alter the
Beagle Glacier dynamics and to allow ice stabilization
and interrupt the general headward recession. Future
studies will probably lead to a discussion of the chronostratigraphy of the lowest moraine arcs in Ushuaia, previously defined as Ushuaia Drift (Rabassa et al., 1990b).
Radiocarbon ages of the terminal moraine complex at
Punta Segunda are still needed to adjust the chronology
in this region.
The 10 ka glacial retreat was definitive: basal peat
layers of Punta Pingüinos in Ushuaia (20 m a.s.l.) and
Lapataia (20 km westward, 18 m a.s.l.; see Fig. 1c)
showed ages of 10,080 14C yr BP (Rabassa et al., 1986;
Heusser and Rabassa, 1987), a condition observed also
for the glaciers that were tributaries to the glaciation axis
located in the eastern end (66 W, Bahı́a Aguirre, Penı́nsula Mitre, Fig. 1c), where basal peat layers have yielded
an age of 10,920 + 70 14C yr BP (UTC-5402). The rapid
disappearance of the ice within the eastern portion of the
Beagle Channel was probably due to the collapse of a
floating ice snout, as sea level invaded the valley and
rose to almost present positions around 8.7 14C ka BP
(Gordillo et al., 1993).
A glacierization model in mountain valleys of the
Fuegian Andes, tributaries to the Beagle Channel valley,
was proposed by Coronato (1995 a, b) and Coronato et al.
(2004b). The transversal and longitudinal valleys of the
Fuegian Andes show the effect of extensive Pleistocene
glacier erosion. The tributary valleys were occupied by
multiple valley glaciers, ranging from 20 to 30 km in
length, though smaller, single-valley glaciers were also
present.
These valleys probably underwent the same sequence
of glacial events as the rest of Tierra del Fuego, but such
episodes are not represented in the existing geological
record. This is probably due to erosion during the LGM.
Moreover, the entire study area was mostly ice-covered
and well above the ELA, impeding the formation of
lateral moraines. As in all interdependent ice system,
glacial activity in the tributary valleys was controlled
by the behavior of the main ice stream and regional
climatic variations. Several phases that took place
between the Late Pleistocene and the Early Holocene in
the Andean valley glaciers have been established: (i) the
LGM, (20–18 14C ka BP); (ii) ‘‘Individualization’’, as the
Moat Glaciation was decaying (18–14 14C ka BP); (iii)
‘‘Stabilization’’, when the ice bodies achieved their maximum positions during Late Glacial times (14–12 14C ka
BP); and (iv) ‘‘Deglaciation’’ (10–9 14C ka BP), when
glaciolacustrine environments were dominant in the
mountain valleys.
14
Els AMS
LPCT
00008
22-1-2008
14:06
Page:183
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
Fig. 31. Kame and glaciolacustrine deposits at the mouth
of the Rı́o Pipo valley, Beagle Channel, near Ushuaia,
Tierra del Fuego, Argentina (Fig. 1c). These were formed
as the valley glacier receded and sediments poured from
the main Beagle Glacier, still occupying the valley during
Late Glacial times. (Photo by J. Rabassa, 2003).
17
18
19
20
21
22
23
24
The erosive landforms are recognizable in the rocky
arêtes in which glacial peaks, horns and cirques abound,
some of them still bearing mountain glaciers of significant magnitude. Glacial accumulation landforms are rare,
although some depositional features have been modeled
in subglacial, supraglacial and marginal ice environments. The presence of latero-frontal moraine arcs,
basal moraines, kame terraces, glacial plains and peat
bogs has been clearly defined and mapped in the valleys
involved, as well as the remains of glaciolacustrine
bodies (Coronato, 1990, 1995a, b). The frontal moraine
arcs of the Andorra and Cañadón del Toro valleys, near
Ushuaia, are separated by glaciolacustrine deposits that
are also present in the Pipo valley. In that valley, icemarginal landforms related to the general glacier recession prevailed (Coronato, 1993; Fig. 31).
The Carbajal–Tierra Mayor valley (Fig. 1c) is another
important glaciation axis in the Fuegian Andes, tributary of
the Beagle Channel at Bahı́a Brown, 50 km east of Ushuaia
(Fig. 1c and Fig. 32). During the maximum of the LG a
trunk glacier established here, flowing from W to E along
the tectonic alignment Carbajal–Tierra Mayor–Lasiparshak
(Fig. 1c), with minor tributary glaciers, coming from lateral
cirques. Due to glacial diversion, an overflowing ice tongue
would have displaced southward along the Rı́o Olivia
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
183
valley down to its confluence with the Beagle Glacier,
E of Ushuaia (Coronato, 1995a, b). The Late Glacial–Early
Holocene depositional sequence is presently under study
concerning the palynological and paleoclimatic aspects.
Geomorphological evidence found in the Fuegian
Andes indicates that the definitive deglaciation process
would have started after 10 14C ka BP. In the inner
valleys, a lacustrine phase has been characterized, in
lake sedimentary sequences or at the base of the present
peat bogs (Coronato, 1991; Gordillo et al., 1993;
Coronato, 1995a, b). The existence of paleolakes in different relative positions in between confluent glaciers
has been dated ca. 10–9 14C ka BP (Coronato, 1993).
Moraines situated close to the cirque basins above
Ushuaia appear to be late glacial in age, but precise
dating remains to be done. Planas et al. (2002) mapped
the geomorphological units within the Martial Glacier
cirque, near Ushuaia (Fig. 1c), with at least two moraine
levels of Late Glacial age developed on both valley sides
and Holocene moraines occurring next to the ice front,
the latter still lacking plant colonization (Planas et al.,
2002; Figs 33 and 34). Some support for a Late Glacial
age cold interval came from the interpretation of pollen
diagrams obtained for this area (Heusser, 2003). These
records showed that a significant reduction in Nothofagus
pollen occurred during the interval ca. 13–10 14C ka BP
(Heusser, 1989a; Rabassa et al., 1990a). Such a decline
has been associated with a significant climatic deterioration, perhaps coeval with glacier advance.
The Late Glacial history of Patagonia and Tierra del
Fuego is now much better known than only two decades
ago, but much precise dating is still needed if definitive
correlation with Northern Hemisphere climatic events is
intended.
4.4. Holocene Glaciation
Mercer (1965, 1968, 1970, 1976, 1982) published pioneer studies on Patagonian Holocene ice advances and
termed them ‘‘Neoglaciations’’. Mercer (1976) found
evidence that by ca. 13 14C ka BP deglaciation had
cleared ice from the Rı́o Baker valley, which separates
the two Patagonian ice fields (Fig. 1a), and concluded
that glaciers in the region did not readvance again until
about 5 14C ka BP. Investigations of moraines lying
several kilometers from the present glaciers on the eastern and western sides of the two Patagonian ice caps
led Mercer (1968, 1970, 1976) to conclude that three
50
51
52
53
54
55
56
57
58
59
60
Fig. 32. Panoramic view of the Carbajal valley, heads of the Rı́o Olivia, near Ushuaia, Tierra del Fuego, Argentina
(Fig. 1c). Erosional glacial landscape, carved on metamorphic rocks during the LG. (Photo by J. Rabassa, 2004).
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
184
22-1-2008
14:06
Page:184
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
Fig. 33. View of the lateral, cirque moraines of Late
Glacial age, Martial Cirque, Fuegian Andes. The city
below the cirque is Ushuaia, and an ample view of the
Beagle Channel (Fig. 1c). The cirque moraines are
actively covered by periglacial fans and talus, coming
down from the summit areas. (Photo by J. Rabassa, 2004).
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Fig. 34. Holocene moraines, Martial Cirque, Ushuaia
(Fig. 1c). (Photo by J. Rabassa, 2004).
41
42
iceshed occurred as the Patagonian ice fields built up
over two mountain ridges separated by an intermontane
depression. Clapperton (1993) has also suggested that the
Patagonian ice fields may not have existed until the
Neoglacial cooling and that only small glaciers restricted
to the (now-buried) mountain ridges survived during the
preceding interval of Hypsithermal warmth.
Palynological studies of cores taken in the Chilean
Lake District (Heusser, 1974; Heusser and Streeter,
1980; Heusser et al., 1981; Fig. 1b, Site 13) also
indicate three cooling intervals during the last 5 kyr.
Radiocarbon dating of major vegetational changes that
indicate cooler conditions suggested that the climate
reversals occurred at 4950–3160 14C BP, sometime
between 3160 14C BP and 890 14C BP, and during the
last 350 yrs. The intervals of relatively low temperature
appear to have coincided with periods when precipitation
was significantly higher than now, with total annual
rainfall as much as 150% above the present mean
(Heusser and Streeter, 1980).
Bertani et al. (1986) recognized at least two Neoglacial advances in addition to that of the Little Ice Age
(LIA) at the Castaño Overo Glacier (Monte Tronador,
northern Patagonia; Figs 1b, Site 12; Figs 35 and 36), and
Rabassa et al. (1984) and Brandani et al. (1986) noted
that the Rı́o Manso Glacier had advanced at least once
before the LIA (Fig. 37). However, none of these earlier
events has been precisely dated yet. The LIA extended
between middle seventeenth and middle nineteenth centuries, based on dendrochronological analysis of the trees
colonizing the successive moraine ridges (Rabassa
et al., 1984; Brandani et al., 1986). Rabassa et al.
(1981) described in-transit moraines on the Casa Pangue
Glacier (western slope of Monte Tronador, Chile), which
supported forest colonization on the active glacier in
those times (Fig. 38).
Although the earliest Holocene has generally been
considered an interval of ameliorating climatic conditions, Röthlisberger (1987) and Röthlisberger and Geyh
(1985) concluded that glaciers advanced at least twice
between 8600 and 8200 14C yr BP. These events were
43
44
advances had occurred during an interval of Neoglacial
cooling that spanned the last 5 kyr. The first was at
4700–4200 14C BP, the second at 2700–2000 14C BP and
the third has taken place during the last three centuries
(seventeenth to twentieth centuries). Most of the organic
material from which radiocarbon dates were obtained gave
only minimal ages for the advances, however, and none
have been closely bracketed. Nevertheless, there is agreement with the ages of Neoglacial fluctuations determined
in other parts of the Andes and in the Northern Hemisphere (Clapperton, 1993). Clapperton (1993) studied all
of Mercer’s data on Neoglacial glacier fluctuations and
noted that an interesting pattern exists. During the first
advance at 4700–4000 14C BP glaciers in the west were
more extensive than during the advance at 2700–2000
14
C BP; glaciers in the east were less extensive at
4700–4200 14C BP than at 2700–2000 14C BP. A preliminary hypothesis is that an eastward migration of the
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Fig. 35. Castaño Overo Glacier, Monte Tronador, northern
Patagonia, Argentina (Fig. 1b, Site 12; photo by J. Rabassa,
1975). This regeneration cone, reconstructed below a very
high ice fall, melted away in recent years due to regional
warming (see Bertani et al., 1986).
Els AMS
LPCT
00008
22-1-2008
14:06
Page:185
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
185
01
02
03
04
05
06
07
08
09
10
11
12
13
14
Fig. 38. Casa Pangue Glacier, Monte Tronador, Chile
(Fig. 1b, Site 12). This is the largest glacier in northern
Patagonia. This is a debris covered, reconstructed
glacier which supported in-transit moraines with soils.
Vegetation was growing on top of the active ice (Rabassa
et al., 1981). (Photo by J. Rabassa, 1979). In the 1990s,
regional warming forced the collapse of the underlying
ice, and with it, the soils and trees.
15
16
17
18
19
20
21
22
23
24
25
26
27
Fig. 36. Art Bloom (Cornell University) posing as scale
on a striated glacial boulder in front of Castaño Overo
Glacier, Monte Tronador, Argentina (Fig. 1b, Site 12;
photo by J. Rabassa, 1982).
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
Fig. 37. Rı́o Manso Glacier, Monte Tronador, Argentina
(Fig. 1b, Site 12). This is a debris covered glacier that
has prominent Holocene and LIA moraines, which can be
seen on both sides of the glacier (Rabassa et al., 1978).
(Photo by J. Rabassa, 1983). This glacier is presently
undergoing very rapid retreat due to regional warming.
48
49
50
51
52
53
54
55
suggested on the basis of volcanic ashes covering apparent Neoglacial moraines and should be considered as
minimal ages only; the moraines could be much older,
possibly even of Late Glacial age.
Glacial advances in the earliest Holocene have been
discussed for a long time. There has been a general agreement that ice readvances suggested for this interval either
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
have been wrongly dated or have been misinterpreted; for
example, some were probably associated with glacier
surges, kinematic waves or other oscillations related to
internal glacier dynamics independent of climatic change
and do not reflect global or regional cooling.
Palynological interpretations in southern Chile by
Heusser (1974) suggested that the warmest climate interval following the Late Glacial cooling occurred between
ca. 8500 and 6500 14C yr BP, when temperatures averaged about 2C warmer than now. This corresponds well
with data from other parts of the world indicating that
Holocene Hypsithermal conditions had peaked before ca.
6000 14C yr BP; but a subsequent study by Heusser and
Streeter (1980) suggested that the maximum warmth had
occurred earlier, between 9410 and 8600 14C yr BP.
Porter (2000) extensively discussed the nature and
age of the Patagonian Holocene glaciations. Evidence
of early Neoglacial expansion of glaciers in the Andes
was primarily located within a belt extending between
46 and 52 S. The glaciers of this area included landterminating alpine glaciers as well as tidewater- and lakecalving glaciers that drain the north and south Patagonian
ice fields (Fig. 1a). On the Chilean side of the southern
Andes, the San Rafael Glacier is a large tidewater glacier,
flowing from the northwestern sector of the North Patagonian Ice Field (Warren et al., 1995a). The Témpanos
moraines (Muller, 1959; Heusser, 1960) border the
Laguna de San Rafael beyond the glacier margin. A
kettle (Lago 1) west of Laguna San Rafael on the outermost moraine was cored by Heusser (1960), who
obtained an age of 3610 + 400 14C yr BP (later recalculated at 3740 + 400 yrs BP; Heusser, 1964) for peat at a
depth of 2.1 m that was overlying laminated silt layers.
Based on this date, Heusser inferred that the earliest
(Témpanos I) advance culminated ca. 4000 14C yrs ago.
Mercer (1982) subsequently suggested that the initial
Témpanos advance likely dates to ca. 4700–4200 14C yr
BP, consistent with then available evidence in the
Els AMS
LPCT
00008
186
01
AU13
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
22-1-2008
14:06
Page:186
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
southern Andes. Clapperton and Sugden (1989) indicated
that the date provides only an upper limiting age for a
moraine that could be much older. A second limiting date
was obtained from a site inside the limit of nineteenthcentury moraines, where 75 cm of unweathered till overlies sand and peat. Compressed wood in the peat has an
age of 6850 + 200 14C yr BP. Heusser (1960) considered
that this date was providing a lower limiting age for the
initial Témpanos advance, the beginning of which he
placed at ca. 5000 14C yr BP. Muller (1959) inferred
that the overlying till at this locality dated to the nineteenth century, and that the date for the wood represented
an upper limiting age for the Témpanos advance. He
suggested that late glacial recession from the Témpanos
moraines took place ca. 9000 14C yrs ago. Mercer (1982)
did not agree with this chronology, noting that it did not
explain why organic sedimentation would only have followed deglaciation 5000 yrs later. Porter (2000) suggested that further studies are needed on this glacier.
However, as San Rafael is a calving glacier, a major
advance of its terminus may not correlate with regional
climatic events (Warren, 1993; Warren et al., 1995b).
Porter (2000) summarized also the knowledge for
other glaciers in the area. The Ofhidro Sur Glacier is an
outlet glacier of the South Patagonian Ice Field (Fig. 1a)
with a grounded snout. However, during Late Glacial
times, its terminus calved into a fjord. Mercer (1970)
stated that its snout was located at 2500 m from the
fjord head and was bordered by a series of recent moraines, the innermost of which dated to the eighteenth
century. At the time when the outermost moraine was
constructed, the terminus was perhaps in contact with
tidewaters. Basal peat from the crest of the second moraine was dated at 4060 + 110 14C yr BP; a similar sample from the sixth moraine had an age of 3740 + 110
14
C yr BP. Mercer (1970) estimated that the second moraine was built no later than ca. 4200 14C yr BP, but the
outermost moraine was not dated.
The Témpano Glacier is an outlet glacier of the South
Patagonian Ice Field, ending at the Témpano fjord along
a calving front. Mercer (1970) dated basal peat from a
bog lying between the outer moraine and the adjacent
hillside at 4120 + 105 14C yr BP, providing a minimum
age for moraine construction. Probably, being a tidewater
glacier, this advance might correspond to local conditions
unrelated to regional climatic variations. At the Los
Cipreses Glacier, Röthlisberger (1987) described four
lateral moraines lying inside deposits more than 6700
14
C yr BP old, also postdating a paleosol with a date of
5180 + 295 14C yr BP. Other outer moraines have not
been dated.
On the Argentinian side of the southern Andes, the
San Lorenzo Este Glacier is a large land-terminating
glacier on the eastern side of Cerro San Lorenzo (Fig.
1b, Site 32), ca. 100 km northeast of the South Patagonian Ice Field. Mercer (1968, 1976, 1982) described two
end moraines bordering the glacier and three older ones.
The outermost moraine dammed a small lake, where a
rooted tree stump was dated at 4590 + 115 14C yr BP,
the tree presumably having been drowned by a glacier
advance. It is possible that local factors may have influenced the behavior of this glacier.
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
The Narváez Glacier is located about 50 km east of
the South Patagonian Ice Field. It shows a proglacial lake
and three moraines. Mercer (1968) inferred that the inner
moraine dated to the nineteenth century and the outer to
the seventeenth century. Basal peat on the outermost
moraine had been dated at 4320 + 110 14C yr BP, providing a minimum age for that moraine. Wenzens (1999b)
studied moraines of the Rı́o Manga Norte Glacier, on the
eastern slope of the Precordillera between Lago Viedma
and Lago Argentino (Fig. 1b, Sites 25, 26), inferred to date
to the LG and postglacial times. Terminal Neoglacial
moraines were dated as older than 4280 + 100 14C yr
BP, but this may not be close to the real age. Dates of
8350 + 50 and 8694 + 45 14C yr BP were obtained from
deposits downvalley from the late Neoglacial limit in
nearby Arroyo Guanaco, and another date of 7370 + 70
14
C yr BP was obtained ca. 12.5 km downvalley from late
Neoglacial moraines in the adjacent valley of Rı́o
Guanaco. According to Porter (2000), further studies are
needed to determine whether these moraines could be
of pre-Neoglacial age, either Early Holocene or Late
Glacial.
The famous Moreno Glacier (Fig. 1b, Site 29) is a
large outlet glacier of the South Patagonian Ice Cap,
calving into Lago Argentino and Brazo Sur, and which
has been permanently advancing during the last century
(Fig. 39). Mercer (1968) obtained a date of 3830 + 115
14
C yr BP for basal peat indicating the end of a glacier
advance. A similar age (3860 + 115 14C yr BP) suggested
that the glacier had retreated by that time. Porter (2000)
mentioned that the earliest lake-damming advance of Moreno Glacier occurred ca. 4850–5050 14C yr BP ago, and a
date of 4640 + 40 14C yr BP for wood in a moraine
probably provides a close age for the maximum of the
most extensive Neoglacial advance. Warren (1994)
pointed out that the unusual behavior of Moreno Glacier
has been more closely controlled by calving dynamics and
topography than by regional climate trends.
Fig. 39. Moreno Glacier (Fig. 1b, Site 29). A large outlet
glacier of the Southern Patagonian Ice Field, Argentina,
which has advanced almost constantly over the last two
centuries across Lago Argentino (Fig. 1b, Site 26),
blocking drainage and causing the lake level to rise.
The pressure of the water finally breaks the ice wall,
bursting the snout of the glacier in a remarkable,
recurrent natural event. (Photo by J. Rabassa, 2004).
Els AMS
LPCT
00008
22-1-2008
14:06
Page:187
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
The Frı́as Glacier, further south, shows Neoglacial moraines along the southwestern shore of Brazo Sur of Lago
Argentino (Fig. 1b, Site 26). Mercer (1968, 1976) described
three moraines dating to recent centuries, obtaining a date of
3465 + 130 14C yr BP from wood on top of the outermost
moraine. He assigned the moraine to an early Neoglacial
age (i.e. ca. 4600–4200 14C yr BP), but the moraine may be
actually younger than this event. The O’Higgins Glacier is a
lake-calving glacier flowing from the Southern Patagonian
Ice Field (Fig. 1a). Röthlisberger (1987) obtained radiocarbon dates for in situ wood fragments between
4675 + 120 and 6020 + 75 14C yr BP.
Porter (2000) concluded that, due mostly to a lack of
multiple and precise dating, the hypothesis that Southern
Hemisphere glaciers advanced more or less synchronously
in the Middle Holocene, and in concert with Northern
Hemisphere glaciers, has not yet been rigorously proven.
Glasser et al. (2004) presented evidence for Holocene
glacier fluctuations of the Patagonian ice fields. These
authors considered that during the early Holocene
(10,000–5000 14C yr BP) atmospheric temperatures east
of the Andes were about 2C above modern values in the
period 8500–6500 14C yr BP. The period between 6000
and 3600 14C yr BP appears to have been colder and
wetter than present, followed by an arid phase from
3600 to 3000 14C yr BP. From 3000 14C yr BP to the
present, there is evidence of a cold phase, with relatively
high precipitation. West of the Andes, the available evidence points to periods of drier than present conditions
between 9400–6300 and 2400–1600 14C yr BP. Holocene
glacier advances in Patagonia began around 5000 14C yr
BP, coincident with a strong climatic cooling around this
time (the Neoglacial interval). Glacier advances can be
assigned to one of three time periods following a
‘‘Mercer-type’’ chronology, or instead, four time periods,
following an ‘‘Aniya-type’’ chronology (Aniya, 1995).
The ‘‘Mercer-type’’ chronology has glacier advances
4700–4200 14C yr BP; 2700–2000 14C yr BP and during
the LIA (seventeenth to twentieth centuries). The ‘‘Aniyatype’’ chronology has glacier advances at 3600 14C yr BP,
2300 14C yr BP, 1600–1400 14C yr BP and during the LIA.
These chronologies are best regarded as broad regional
trends, since there are also dated examples of glacier
advances outside these time periods. Possible explanations
for the observed patterns of glacier fluctuations in
Patagonia include changes related to internal characteristics
of the ice fields, changes in the extent of Antarctic sea-ice
cover, atmospheric/oceanic coupling-induced climatic
variability, systematic changes in synoptic conditions and
short-term variations in atmospheric temperature and
precipitation.
Douglass et al. (2005) used cosmogenic nuclide surface exposure dating to show that at least one glacier on
the Chilean side of Lago Buenos Aires (46 S; Fig. 1b,
Site 24) advanced ca. 8.5 and 6.2 14C ka BP. These data
on the so-called Fachinal moraines suggest that the ice
advanced most likely as a result of a northward migration
of the southern westerlies, which caused an increase in
precipitation and/or a decrease in temperature at this
latitude. The older advance is 3000 yrs older than the
accepted beginning of Holocene glacial advances in
southern South America (Mercer, 1976). According to
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
187
these authors, these events are temporally synchronous
with Holocene climate oscillations that occurred in other
parts of the world. If there are causal links between these
events, then rapid climate changes appear to be either
externally forced (e.g. solar variability) or are expanded
shortly all over the surface of the Earth by atmospheric
processes.
After 10 14C ka BP, ice persisted only as cirque glaciers
and small valley glaciers in the eastern Fuegian Andes, and
as remnants of a mountain ice sheet in the Darwin Cordillera
(Fig. 1a; Rabassa et al., 1992; McCulloch et al., 1997).
In the Andorra and Cañadón del Toro valleys, near
Ushuaia (Fig. 1c), the cirques are dominantly oriented
toward the S, SE and SW. The ice occurrence/orientation
relationship shows concordant aspects with the hemispheric insolation and the regional climatic conditions,
because ice relicts are still present facing toward the SE
(45.1%) in the Andorra valley, to the S (18.5%) in the
Cañadón del Toro, to the SW (16.1% and 33.3%) in the
Andorra valley and Cañadón del Toro (Coronato, 1995a).
Recession followed the late glacial maxima and evidence for several Neoglacial readvances are observed in
the cirques. Three moraine arcs have been mapped at the
Vinciguerra Glacier, near Ushuaia, the largest cirque
glacier still existing in the Argentine Fuegian Andes
(Fig. 1c). The oldest moraines reach 600–650 m a.s.l.
and have been largely colonized by the Fuegian forest.
The youngest one lies well above the timberline. This
moraine was apparently formed during the LIA; older
readvances are represented by complex moraine systems,
but all of them remain undated.
The occurrence of ice bodies within the glaciated
valleys is restricted to a minimum elevation of
700–800 m a.s.l. The topography of the glacier valleys
clearly shows the Holocene events. These were defined
as (a) the Vinciguerra I phase (8.5–5.0 14C ka BP), when
the glacier receded continuously without evidence of
stabilization; (b) the Vinciguerra II phase (5.0 14C ka BP)
represented the stabilization of the glacier, generating
lateral moraines at 500–540 m a.s.l., and the erosional landforms on the first threshold at 480–600 m a.s.l., and (c) the
last phase, or Vinciguerra III (LIA), corresponded to a
second stabilization event with two well-developed
pulsations, depicted by moraines formed within the present
forefield (Rabassa et al., 1992).
4.5. Glaciation of Islas Malvinas/Falkland Islands
Quaternary studies on the Islas Malvinas/Falkland
Islands (Fig. 1a) started as early as the mid-nineteenth
century, when Darwin (1846) described the presence of
distinctive periglacial features like block streams or
‘‘stone rivers’’.
The existence of Pleistocene glaciers in the archipelago was demonstrated by Clapperton (1971), Clapperton
and Sugden (1976), Roberts (1984) and Clapperton and AU14
Roberts (1986), among others, and summarized by
Clapperton (1990, 1993). During the Quaternary, only
conditions for marginal glaciation had developed,
whereas at the same latitude, very large ice fields existed
in Patagonia. Roberts (1984) identified 76 nivoglacial
Els AMS
LPCT
00008
188
22-1-2008
14:06
Page:188
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
features, made up of 8 nivation crests, 41 nivation hollows,
7 nivation cirques and 20 glacial cirques. Erosional and
depositional characteristics identified on the islands suggest that there were at least two intervals of cirque glaciation. Three glacial cirques are larger than the rest, but they
also show the development of cirque-in-cirque glaciation.
A few glaciers expanded beyond the cirque basins and
deposited till and terminal moraines in the valleys. Roberts
(1984) suggested that the Pleistocene glacial history of the
archipelago is restricted to only three events: an early
cirque phase, a valley phase and late cirque phases. The
latter probably represents the LGM.
The entire archipelago is affected by periglacial mass
wasting, suggesting that Quaternary cold periods are
largely responsible for landscape development. According to Clapperton (1990), a radiocarbon date of
26,060 þ 400/–380 yrs BP, for a podsol buried by
1.5 m of solifluction debris, suggests that the last interval of solifluction probably coincided with the LGM.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
4.6. Modeling the Late Pleistocene Ice Sheet
and Glacier Behavior
22
23
24
Sugden et al. (2002), Hulton et al. (2002) and Hubbard
et al. (2005) have tried to model the expansion and recession of the Patagonian Ice Sheet during the LGM. Hulton
et al. (2002) used a coupled ice sheet/climate numerical
model with empirical evidence, simulating the ice sheet at
the LGM and at different stages of deglaciation. Under
LGM conditions, an ice sheet with a modeled volume
slightly in excess of 500,000 km3 built up along the southern Andes. There is a marked contrast between the maritime and continental flanks of the modeled ice sheet. The
model is most sensitive to variations in temperature and
there is good agreement between modeled ice extent and
empirical evidence. This was achieved by applying an
estimate of a 6.1C temperature decrease with constant
wind. Assuming a stepped start to deglaciation, modeled
ice volumes declined sharply, contributing 1.2 m to global
sea level, of which 80% occurred within only 2000 yrs.
The empirical record suggested that such a stepped warming occurred around 17,500–17,150 cal. yrs ago.
Hubbard et al. (2005) presented a time-dependent
model to investigate the interaction between climate,
extent and fluctuations of Patagonian ice sheets between
45 and 48 S during the LGM and the deglaciation that
followed. The model was applied at 2 km resolution and
enabled ice thickness, lithospheric response and ice
deformation and sliding to interact freely. Relative
changes in sea level and ELA were considered as well.
Experiments implemented to identify an LGM configuration compatible with the available empirical record indicated that a stepped ELA lowering of 750–950 m was
required over 15,000 yrs to fit the Fénix I–V moraines at
Lago Buenos Aires (Fig. 1b, Site 24). However, 900 m of
ELA lowering yielded an ice sheet that best matches the
Fénix V moraine (ca. 23,000 14C yr BP) and Caldenius’
reconstructed LGM limit for the entire modeled area.
According to these authors, this optimum LGM experiment yielded a highly dynamic, low aspect ice sheet, with
a mean ice thickness of ca. 1130 m drained by numerous
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
large ice streams to the western, seaward margin and two
large, fast-flowing outlet lobes to the east. Forcing this
scenario into deglaciation using a rescaled Vostok ice
core record resulted in a slowly shrinking ice sheet that
was only 25% of the LGM volume by ca. 14,500 14C yr
BP, after which it collapsed rapidly, with a loss of 85% of
its volume in only 800 yrs. It is interesting to note that its
margins stabilized during the ACR, after which it receded
to near present-day limits by 11,000 14C yr BP.
Wenzens (2004) has strongly criticized Sugden et al.
(2002) models, and implicitly, his criticism applied also
to Hubbard et al. (2005) later work. Wenzens (2004)
estimated that the boundaries depicted in the models do
not fit with any actual ice margin of comparable age, that
the considerations did not apply to both Patagonian ice
sheets and that the Andean topography had not been
properly considered in the models.
Another point of view is presented by Benn and
Clapperton (2000b), who described proglacial and subglacial glaciotectonic sediments and landforms around
the margins of the Strait of Magellan. These deposits
recorded the advance and retreat of outlet glaciers of
the Patagonian ice cap during the Last Glacial cycle.
The glaciotectonic landforms in the area would have
been the result of advancing ice lobes with cold-based
margins due to permafrost regional conditions, but with
wet-based inner portions. As the ice advanced, subglacial
basins would have been dug underneath the glacier margins and the eroded material was pushed up into thrust
moraines, probably because frozen-bed conditions
formed a thermal dam against the free drainage of subglacial meltwaters. Later, these ice-marginal glaciotectonic landforms would have been overridden and
streamlined into drumlins and flutes when thicker, wetbased ice advanced over these areas. Evidence for permafrost near sea level in Patagonia during the Last
Glaciation suggests that mean annual temperatures were
several degrees lower than indicated by recent modeling
studies. The results indicate that future modeling experiments should incorporate more realistic basal boundary
conditions, particularly the presence of a weak deforming
layer at the glacier bed, to improve climatic reconstructions of southern South America.
Concerning interhemispheric links, in the opinion of
Blunier et al. (1998), a main aspect of climate dynamics
is to understand if the Northern and Southern hemispheres are effectively coupled during climate events.
The fast and strong temperature changes observed in
Greenland (the Dansgaard–Oeschger events) during the
last glaciation have a certain analogue in the temperature
record from Antarctica. A comparison of the global
atmospheric concentration of methane as recorded in
ice cores from Antarctica and Greenland allowed establishing a phase relationship of these temperature variations. Greenland warming events between ca. 36 and
45 ka ago have a delay in relation to their Antarctic
counterpart by more than 1 kyr. On average, Antarctic
climate change precedes that of Greenland by 1–2.5 kyr
over the period 47–23 ka. However, it should be considered that the observed delay is usually within the operational error of the dating techniques, and improved data
are needed to confirm these opinions.
Els AMS
LPCT
00008
22-1-2008
14:06
Page:189
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
5. Discussion
01
02
5.1. Environmental Changes in Southern South
America Following the Glacial Events
03
04
05
The Patagonian glacial sequence provides a reasonable
framework to understand the environmental evolution of
southernmost South America from the latest Miocene to
the Pleistocene–Holocene boundary. Particularly, the
relative lack of other long terrestrial records gives a
paramount importance to the glacial evidence for preLate Pleistocene times.
Clapperton (1993), Heusser (2003) and Rabassa et al.
(2005) have discussed the climatic and environmental
changes in southern South America that followed the
establishment and development of the Late Cenozoic Patagonian glaciations, which may be summarized as follows.
First, global sea level changes forced by glaciation
partially exposed the Argentinian submarine platform,
which enhanced the climatic continentality. Significant
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
eustatic movements took place, with sea level lowering
of at least several tens of meters during cold events, and
up to 100–140 m during full glacial episodes. Climatic
continentality of the surrounding areas increased, with
rising extreme temperatures, precipitation diminution and
lack of the sea moderating effect as the coastline moved
eastward. This process occurred both in Pampa and Patagonia, with almost a doubling in size of the continental
areas and subsequent strong continentalization. Note that
for the Latest Pleistocene, this is an important fact
regarding the environmental conditions and available
pathways and space for human colonization in the
Pampean and Patagonian Regions (Fig. 40).
Sea-surface temperatures were lowered up to 4C in
the tropical areas during MIS 2, with at least a lowering of
5–6C in southern South Africa (30–32 S; Tyson and
Partridge, 2000), with increased lowering toward the
poles. This lowering in mean sea-surface temperature
(MSST) had certainly influence on the evaporation and
mobility of marine currents, with a consequent diminution
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
AU15
Font: Times
Fig. 40. Map of South America during the LGM. Partly modified from Clapperton, 1993.
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
189
Els AMS
LPCT
00008
190
22-1-2008
14:06
Page:190
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
of mean annual temperature in all continental areas, which
in northern Patagonia would have been of at least 5–6C
and perhaps much more in the southern regions (Heusser,
1989b; Clapperton, 1993).
These conditions increased the influence of the Malvinas/Falkland Current (Fig. 40), which today reaches up
to southern Brazil. Most likely, this current reached a
much more northerly position during the glacial winters,
and stayed there for longer portions of the year. As a
consequence of the coastline mobility, the position of the
littoral marine currents, both the Brazil and Malvinas/
Falkland currents were affected. During the glacial
epochs their meeting front was displaced northward,
modifying the Pampean winter storm pattern, and probably, diminishing the oceanic influence and increasing
water deficit during these periods.
Moreover, sea level lowering provoked a strong lowering of marine depth between the Patagonian coast and
the Malvinas/Falkland Archipelago, forcing an eastward
displacement of the Malvinas/Falkland Current, with a
further increase in climatic continentality along the present littoral zones.
The climatic conditions during glacial episodes had
an influence on the displacement of the oceanic anticyclonic centers, both in the Pacific and in the Atlantic
oceans. The South Pacific anticyclonic center was displaced northward during the glacial periods, increasing
the effect of the ‘‘Pampero’’, cold-dry winds that dominate the weather and eolian sedimentation in the Pampas
of eastern Argentina, Uruguay and southern Brazil. The
northward movement of this anticyclonic area determined that those regions previously free of the cold and
dry ‘‘westerlies’’ were progressively affected by these
winds. The increasing eolian action leads to the development of intensive deflation processes, with the genesis of
hydroeolian depressions, salt lakes and endorheic basins,
and also the dune field formation in northern Patagonia
and western Buenos Aires Province (Clapperton, 1993;
Iriondo, 1999; Fig. 41). This eolian activity was also
responsible for loess accumulation in the Pampean
Region, Uruguay and southern Brazil, beyond the dune
belts, where the Pampean vegetation, though thinner than
in interglacial times, was capable of retaining the fine
sand-coarse silt fractions. A similar role had the Rı́o
Salado of Buenos Aires Province (35 S, Buenos Aires
Pampean Region, Fig. 1a), which acted as a sand trap,
originating the La Chumbiada (Dillon and Rabassa,
1985) and Guerrero (Fidalgo et al., 1975) members of
the Luján Formation, during the Late Pleistocene (MIS 4
to 2). Similar conditions would have taken place in most,
if not all, glacial events of the rest of the Pleistocene and
before, since the Rı́o Salado has long been occupying a
very ancient tectonic basin (Rabassa et al., 2005). Moreover, it is also probable that a northward displacement of
the anticyclonic centers generated changes or at least a
higher variability in the eolian sediment supply contributing to the Pampean loess formation, incorporating epiclastic products coming from western Argentina and the
central Andes (Iriondo, 1999; Muhs and Zárate, 2001).
As a consequence, deflation was strongly dominant
during all glacial events, with formation of sand dunes
and loess mantles in the Pampas, excavation of endorheic
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Fig. 41. Sand sea and loess accumulation in the Pampas
and surrounding lowlands during the LGM. From
Iriondo, 1999.
hollows and depressions, and genesis of salt lakes in
areas that are wetter today.
Climatic changes forced changes in the plant cover,
with large latitudinal displacements of the major ecosystems during glaciations.
Tundra, which is restricted today to mountain summits above the treeline, developed all over southern Patagonia, and perhaps up to 42–44 S. Tundra conditions
included permanent or transient frozen ground, at least
around the ice margins, though its eastward expansion
could have been larger (C. Heusser, in Bujalesky et al.,
1997). Tundra paleoenvironment, inferred from palynological records of fossil peat at Lago Fagnano, near
Tolhuin (Fig. 1c; Bujalesky et al., 1997), was characterized by the absolute lack of arboreal (Nothofagus spp.)
pollen, while it was dominant during a glacial phase
of the penultimate glaciation (MIS 6) and, most likely,
was also present during the LG. Still unpublished palynological studies of fossil peat layers interbedded with
tills in the area have confirmed these environmental
conditions (J.F. Ponce, personal communication). See
also Coronato et al. (2004c) and Trombotto (Chapter
12), for ice-wedge cast development in northern Tierra
AU16
del Fuego during the Last Glaciation.
In Late Glacial times as the glaciers receded, this
tundra environment was probably rapidly replaced by a
park vegetation, with isolated Nothofagus spp. forest
patches in a grassy steppe environment. These conditions
are particularly evident in the Harberton peat bog (Fig. 1c)
pollen profile (Heusser, 1989), where the recession of the AU17
‘‘Beagle Glacier’’ from its outermost LGM positions
allowed the partial recovery of the Fuegian forest as
early as 14.8 14C ka BP. At that moment, and for several
hundred years, the forest started its slow but steady
Els AMS
LPCT
00008
22-1-2008
14:06
Page:191
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
AU18
62
Font: Times
recovery, advancing from (still) theoretical refuges located
at the present submarine platform or perhaps at Isla de los
Estados (Staaten Island; Fig. 1a), as suggested by the
pollen record (Coronato et al., 1999). However, in at
least two opportunities, around 13 and 11 14C ka BP,
respectively, the arboreal pollen content practically
disappears from the record, being entirely replaced by
Gramineae and Empetrum, indicating the return to cold
regional conditions, which forced perhaps a new east–
northeastward recession of the Fuegian forest, toward its
Pleistocene refugia. But toward 10.2 14C ka BP, the content
of the pollen records indicates that the forest restarted its
expansion on Isla Grande de Tierra del Fuego, reaching
present-day conditions in the first millenium of the Holocene, though the present conformation of the forest was
achieved only toward ca. 8 14C ka BP. These cold Late
Glacial episodes (herein named as ‘‘late glacial I’’ and ‘‘late
glacial II’’) may be comparable both in chronological and
in intensity terms with their Northern Hemisphere equivalents, the ‘‘Oldest?/Older? Dryas’’ and ‘‘Younger Dryas’’.
Alternatively, a strong influence of the ‘‘Antarctic Cold
Reversal’’ event has been proposed (Sugden et al., 2005).
Nevertheless, the pollen record undoubtedly indicates that
the ‘‘late glacial II’’ event was more intense and extreme
than the previous one, but its environmental consequences
on the forest are still unknown.
The Patagonian forest became isolated from other
South American forest formations perhaps already in the
Middle Miocene. On the Chilean side, as the ice reached
the Pacific Ocean waters south of 44 S, the forest was
probably completely suppressed, perhaps with isolated
refuges on small, remote islands or uncovered coastal
peaks. On the eastern slopes, the forest was concealed in
between the glacier front and the 0C annual isotherm
toward the west, and the shrubby steppe environments
and the 300 mm annual isohyeth eastward, which would
have bounded its eastern expansion. These ecosystems
were severely damaged and the forest was disrupted in
fragmented populations, in remote and restricted refuges,
from 36 southward. In Tierra del Fuego, the forest was
probably displaced toward the present submarine platform,
northwest and north of Penı́nsula Mitre and Isla de los
Estados (Fig. 1a, c; Coronato et al., 1999).
The Pampean grassy prairies were spatially reduced
and pushed north and northeast during glacial events.
Thus, the Patagonian steppe expanded northward into
the Pampean domain and perhaps, even into Uruguay
and northeastern Argentina, thus becoming an important
factor in loess accumulation. The Patagonian equivalents
of the Pampean prairies, which had developed since the
Early-Middle Miocene, disappeared as well, being
replaced by the north- and eastward expanding Monte
and steppe ecosystems (Rabassa et al., 2005).
These ecosystem changes were closely followed by a
significant terrestrial faunal replacement, with northward
expansion of Patagonian faunas during cold events,
reaching up to southern Brazil. Likewise, the Brazilian
faunas invaded the Pampas and even northernmost Patagonia during interglacial periods. This has been proved
for the Late Pleistocene in the Pampean vertebrate fossil
records (Chapter 13) and it was probably in effect during
each major climatic cycle.
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
191
Under drier-colder climate, Patagonian faunas predominated in the Pampas during glacial epochs, and
warmer-wetter Brazilian faunas during the interglacials.
This faunal replacement, clearly observed during the
Pleistocene–Holocene transition and, more recently, in
the Late Holocene, would have probably taken place
with similar characteristics during each glacial ‘‘termination’’, that is, for at least 15 times since the GPG, and
perhaps even 50 or more times since the early Pliocene
and even more than 100 times since the Late Miocene.
The consequences that the high frequency of these displacements would have had on the Pampean faunas, both
from a taxonomic and a biogeographical point of view,
remain still in the hypothetical domain, but they should
not be let aside in paleobiological, paleogeographical and
paleoenvironmental reconstructions in southern South
America (Rabassa et al., 2005).
It is clear then that the climatic cycles identified in the
global oceanic isotopic sequences have been confirmed by
the terrestrial Patagonian glacial record. These changes have
been very important and they should have had a significant
influence in the development of the Pampean and other
South American ecosystems, perhaps up to southern Brazil.
These paleoenvironmental modifications would have
had severe consequences in the entire studied region,
although it is understandable that their characteristics and
intensity would have not been identical over the huge
Patagonian and Pampean geography. But, undoubtedly,
they should have played an important role in the process
of early peopling of Pampa and Patagonia. It is highly
possible that the human expansion in southern South
America would have started immediately after the LGM
(ca. 25 cal. ka) and most certainly, after the last phase of
morainic construction, ca. 16 calendar ka (Lago Buenos
Aires, Fig. 1b, Site 24; Kaplan et al., 2004). The southheading human groups, probably looking for regions with
a higher density of surviving Pleistocene megamammals,
underwent not only the progressive environmental changes
typical of the Last Termination, but they should have
suffered as well the two Late Glacial cold episodes,
which affected them and the regional biota in a similar
manner (Rabassa et al., 2005).
The Pleistocene–Holocene transition, the timing of
the human occupation of Patagonia, was an epoch of
high environmental instability. There was a varied environmental mosaic which, together with locations closer to
the sea and under its influence, would have offered
appropriate, though perhaps different, routes for human
peopling. In those times, environments and thus, faunal
resources would have been equivalent in both Pampa and
Patagonia. These faunas are characteristic of grassland
environments or, at least, grassy steppes of cold, dry to
semiarid climates (Cione and Tonni, 1999). The changes
leading to definitive Holocene environments took place
only after 9 14C ka AP, toward a shrubby steppe, with the
final disappearance of the Pleistocene faunas and increasing abundance of Lama guanicoe (Miotti and Salemme,
1999; Rabassa et al., 2005).
When the Holocene environments were finally established, the glaciers were reduced to their present conditions, thus allowing for full occupation of most of the
Patagonian lands, including the Andean piedmont and the
Els AMS
LPCT
00008
192
01
02
03
04
05
06
AU19
22-1-2008
14:06
Page:192
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
5.2. The Buildup of the Patagonian Ice Sheet
Magellan Straits. Faunas changed from those of drier
environments to others corresponding to higher relative
moisture. The Brazilian faunas occupied the Pampas
during the Late Holocene, and the Patagonian faunas
have been similar to the extant ones throughout the
Holocene (Tonni and Cione, 1999).
The variations in length and frequency of the cold-warm
climatic cycles have determined that the intensity of the
extreme isotopic content peaks of the global oceanic
record became larger toward the Early Pleistocene. Thus,
07
Ma
09
10
Magnetic
Polarity
3.70
3.75
3.80
3.85
3.90
3.95
4
4.1
4.2
4.3
4.4
4.5
11
12
13
14
15
16
17
18
19
20
21
IOS Age
South American
Biozones
Stages
PLIOCENE
08
EARLY
Locali- Source
ties
Sources
1: Mercer, 1983
2: Rabassa, 1999
3: Ton-That et al., 1999
4: Schlieder, 1989
Neocavia CHAPADMALALAN
depressidens
LBA: Lago Buenos Aires
PA: Pampa de Alicurá
C
N
LBA
1
LBA
1
4.6
Basalts layers
Inferred glaciation
22
4.7
23
24
4.8
25
S
M
O
N
T
Trigodon gaudryi E
H
E
R
M
O
S
A
N
26
4.9
27
28
5
5.1
29
C3
T
33
34
35
36
37
38
TG20?
TG22?
C3a
n1
39
40
LBA
2
Overlying basalt
Underlying basalt
PA
4
PA
4
LBA
1
LBA
1
LBA
2
LBA
3
MIOCENE
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
6
6.1
32
Gilbert
30
31
Glaciofluvial
deposits
SI4?
6.2
41
6.3
6.4
42
43
?
44
6.5
6.6
6.7
6.8
6.9
7
7.05
7.1
7.15
7.2
7.25
8
9
10
45
46
47
48
49
50
51
52
53
54
55
C3b
HUAYQUERIAN
C4
C4a
CHASICOAN
56
Fig. 42. Patagonian glaciations during the latest Miocene and Early Pliocene (from Rabassa et al., 2005). The dark bands
correspond to radiometric dated lava flows; the dotted bands correspond to individual tills and the vertical line bands
represent inferred glacial events. Black triangles depict whether the lava flow is used as an upper or lower limiting age for
a certain glacial episode. The columns at the left of the figure represent the chronological global scale in million years, the
global paleomagnetic scale and the global marine isotope stage sequences. The Pampean biostratigraphic units, their
established biozones and stages and their time boundaries have been taken from Verzi et al. (2002).
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008
22-1-2008
14:06
Page:193
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
climate became more extreme and pleniglacial conditions
were gradually achieved at lower latitudes since the
Antarctic Peninsula was glaciated during the Middle
Miocene and piedmont glaciers occurred in Patagonia at
the Latest Miocene. This is due to the fact that, with
shorter and milder cycles, the glacial conditions were not
functional during such periods long enough so as to allow
the building and persistence of extensive ice fields in the
Patagonian Cordillera. Only in the Late Pliocene would
appropriate conditions have been reached so as to develop
a continuous mountain ice sheet, since latitudes from 36 S
to Cape Horn (56 S; Fig. 1c), which would have recurrently grown in each subsequent glacial cycle during the
whole Pleistocene up to the Last Glaciation.
The high climatic variability recorded since the Late
Miocene in Pampa and Patagonia was a consequence of
changes in the astronomical, orbital parameters. These parameters would have been predominant in different times:
(a) equinoctial precession from the Late Miocene to the
Middle Pliocene, developing cycles of ca. 23–19 kyr during
this period; (b) obliquity from the Late Pliocene to the Early
Pleistocene, with cycles of ca. 41 kyr and (c) eccentricity
from the Middle to Late Pleistocene, with cycles of 100 kyr
(see, for example, Ruddiman et al., 1986; Berger and
Loutre, 1991; deMenocal and Bloemendal, 1995; Opdyke,
1995). The shorter cycles would have impeded the formation of the Patagonian mountain ice sheet from the Late
Miocene to the Middle Pliocene, favoring instead the development of local glaciers, of which the sedimentary record is
still scarce (Rabassa et al., 2005).
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
193
5.3. The Correlation of the Patagonian Glaciations
and the Pampean Land Mammal Stages
A correlation of the Patagonian glaciations and paleoenvironmental conditions and the Pampean stratigraphy since the
Late Miocene was proposed by Rabassa et al. (2005). The
Pampean biostratigraphic units have been known since
Ameghino (1889) and thoroughly described by Tonni and
Cione (1995), Alberdi et al. (1995), Pascual et al. (1996),
Tonni et al. (1999a, 1999b) and Verzi et al. (2002), among
many others. The geomagnetic sequence of the continental
Pampean sequences, as presented by Orgeira (1990) and
Nabel et al. (2000), among others, has been the basic tool
for the correlation with the Patagonian glacial sequences.
The correlation results have been shown in Figs 42–44.
The oldest Patagonian glacigenic deposit was formed
during the Late Miocene, in the Montehermosan South
American land mammal (SALMA) stage (Tonni and
Cione, 1995), although it is not yet clear if this corresponds to a glacial event during the colder events MIS
TG 20–22, in the Latest Miocene, or even somewhat later
during MIS Si 4–Si 6 (Earliest Pliocene). In these periods
the global temperatures would have been lower than
during the Early Chapadmalalan (Early Pliocene) land
mammal stage. In the Late Chapadmalalan, local glaciation would have taken place, at least in the Lago Viedma
area (Fig. 1b, Site 25; Figs 42, 43).
Colder than present conditions appeared only since
ca. 2.6 Ma, in the Sanandresian land mammal stage.
Before 3 Ma, the climatic conditions were always
31
32
Age
South American
Stages
Biozones
Locali- Source
ties
2
34
2.15
2.20
2.25
2.30
2.35
2.40
2.45
35
36
37
38
39
40
88
92,96
100
44
45
46
47
AU20
2.80
2.85
2.90
2.95
49
Ctenomys
chapadmalensis
P L I O C E N E
43
Gauss
42
51
52
53
54
55
56
57
58
59
1
LV,CF
LBA
1,2
3
A. (Akodon)
lorenzinii
SANANDRESIAN
M
A
R
P
L
A VOROHUEAN
T
A
N
LV
2
LV,LA
2,4
2
BARRANCALOBIAN
CF: Cerro del Fraile
LA: Lago Argentino
LV: Lago Viedma
Inferred
glaciation
Overlying basalt
LA
5
LV
LV
6
7
LV
6
KM4,KM6
M2
M
MG2
1: Rabassa, 1999
2: Wenzens, 2000
3: Sylwan, 1989
4: Schellmann, 1998
5: Mercer, 1969
6: Mercer, 1976
7: Mercer et al., 1975
Basalts layers
LV
Platygonus
scagliai
K
Sources
Till
3
3.05
3.1
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3.50
3.55
3.60
50
CF
C2
2.50
2.55
2.60
2.65
2.70
2.75
41
48
IOS
Magnetic
Polarity
Ma
33
Underlying basalt
Paraglyptodon
chapadmalense
C2a
LATE
CHAPADMALALAN
MG6
60
Fig. 43. Patagonian glaciations during the Middle and Late Pliocene (from Rabassa et al., 2005). See Fig. 42 for
explanation.
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
14:06
Page:194
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
01
Ma
02
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
03
04
05
06
07
08
09
10
11
12
13
14
15
Magnetic
Polarity
17
18
19
20
21
22
23
24
25
26
27
28
29
42
43
44
2
LBA
5, 4
LA, SO,LBA,T
CF
CF
RG
LBA
6,7,8,4,9
9
9
6,4
5
LA, RG
LA, RG
RG
6,4
7
8
LA, CF
LA
CF
CF
LA
LA, CF
CF
6,9
10
9
9
5
6,7, 11,9
9
18,22
J
30
34
36
E
N
S
E
N
A
D
A
A
N
Tolypeutes
pampaeus
588
Sources
1: Guillou and Singer,
1997
2 : Rabassa and
Evenson, 1996
3: Mercer, 1982
4: Ton-That et al., 1999
5: Sylwan, 1989
6: Mercer, 1976
7: Mercer, 1983
8: Meglioli, 1992
9: Rabassa, 1999
10: Mercer, 1969
11: Schellmann, 1998
41
NH
C1
33
40
4, 2
16
2.1
39
NH,LBA
BONAERIAN
32
38
1
2, 3
12
2
37
LBA
VM,NH,LBA
Megatherium
americanum
2.05
36
Source
LUJANIAN
8?
31
35
Localities
6
30
34
South American
Biozones
Stages
E.(Amerhippus)
neogeus
0.9
0.95
1
1.05
1.1
1.15
1.20
1.25
1.3
1.35
1.4
1.45
1.5
1.55
1.6
1.65
1.7
1.75
1.8
1.85
1.9
1.95
16
IOS Age
PLEISTOCENE
194
22-1-2008
Brunhes
00008
Matuyama
LPCT
Olduvai
Els AMS
62
64
70
72
78
82
VM: Malleo valley
NH: Lago Nahuel Huapi
LA: Lago Argentino
SO: Otway Sound
T: Tronador Mount
CF: Cerro del Fraile
RG: Río Gallegos valley
LA, CF
6,9
LA
6, 9
Basalts layers
Till
Overlying basalt
Underlying basalt
45
46
Fig. 44. Patagonian glaciations during the latest Pliocene and the Pleistocene (from Rabassa et al., 2005). See Fig. 42
for explanation.
47
48
49
50
warmer than the last interglacials (Holocene, MIS 5 and
MIS 7), according to the global isotopic record, with the
exception of short events at 3.12, 3.3, 3.35, 4.8–4.9 and
5.7–5.8 Ma, during the Chapadmalalan and Montehermosan land mammal stages.
Loess-like beds have been mentioned in the older
Pampean units, at least since the Montehermosan land
mammal stage and perhaps even before (see, for example, Zavala and Quattrocchio, 2001). The Pampean loess/
soil sequences are much more poorly developed than
those that have been described in China (Rutter et al.,
1991). This fact is probably due to either (a) the feeble
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
pedogenetic effect during the integlacials or (b) a powerful erosional action over the interglacial soils during the
cold cycles (Rabassa et al., 2005).
The Early Ensenadan land mammal stage is correlated by the recurrent glaciations at Cerro del Fraile
(Fig. 43). The Late Ensenadan is characterized by the
largest extension of the Patagonian glaciers, at the GPG,
and the subsequent, still important ‘‘Daniglacial’’ events.
The Ensenadan stage is the epoch of the astronomical
shift from the 41 kyr to the 100 kyr cycle in the global
record, and the establishment of full glacial conditions in
temperate areas.
Els AMS
LPCT
00008
22-1-2008
14:06
Page:195
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
During the Bonaerian stage (Fig. 44), several smaller
glaciations and the ‘‘Gotiglacial 1’’ events (Early Illinoian; MIS 8–16) took place. Finally, the Lujanan stage
hosted the ‘‘Gotiglacial 2’’ event (Late Illinoian, MIS 6)
and the Last Glaciation (Wisconsinan, MIS 4 to 2).
The analysis of the global isotopic record, the Pampean stratigraphy and the Patagonian terrestrial glacial
evidence contradicts the Mid-Pliocene Antarctic full
deglaciation hypothesis (following Bruno et al., 1997),
because the climate would have stayed within the mean
levels of the glacial/interglacial cycles in that epoch, and
there is no regional evidence of such a very high sea level
that could provide scientific support to this theory.
It must be concluded that during the lapse comprised
from the Montehermosan to the Lujanian stages, there
would have existed at least 50 complete cold-warm
climatic cycles, forcing the regional development of the
Patagonian–Pampean ecosystems. These large-scale
climatic variations should be taken into consideration
when discussing paleoecological, paleobiogeographical
and evolutionary characteristics of the Late Cenozoic
Pampean faunas.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
6. Final Remarks
25
26
When the Antarctic Circumpolar Current became finally
established and the Andean ranges reached elevations
closer, or even higher, than their present positions, regional climatic conditions allowed the frequent development
of glaciation, from the end of the Miocene. However,
glacierization could have started even before, perhaps
11–12 Ma (Wenzens, 2006a) during the final phase of
the Santacruzan–Friasan land mammal stage. However,
these very early and supposedly extensive glaciations
need further confirmation.
The high climatic variability that began in the Late
Miocene is due to Milankovitch cycles. Equinoctial precession would have been dominant during the Late Miocene and
the Early Pliocene, with cycles of ca. 23 kyr. Axis obliquity
would have been largely influential during the Late Pliocene
and the earliest part of the Early Pleistocene, with cycles of
41 kyr. Orbital eccentricity would have prevailed during the
final portion of the Early Pleistocene and later until today,
with cycles of ca. 100 kyr. The shorter climatic cycles of
earlier times would have impeded the formation of the Patagonian Ice Sheet as one single unit during the Late Miocene
and the Pliocene. Thus, it is assumed that only local ice caps
and mountain glaciers would have developed until the Early
Pleistocene when the Patagonian Ice Sheet was finally established (Rabassa et al., 2005).
Though Pampean loess layers from the Late Miocene are known, their occurrence is more frequent since
the Late Pliocene, during the Marplatan land mammal
stage. The Pampean loess/soil sequences are not as well
preserved as their Chinese counterparts. This is probably due to either (a) a poor ‘‘Brazilian’’ (i.e. warmer
climate) effect on the Pampa environments during the
interglacial periods, when pedogenesis should have
taken place, or (b) intense erosion (deflation) during
the colder, arid glacial periods. The thicker loess units
would have been formed only during the 100 kyr cycles,
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
195
that is, the last 1.2 Ma, when the Patagonian Ice Sheet
was fully developed.
The ecological, faunal and floral, mobility of the
Patagonian and Pampean regions, as well as of other
midlatitude areas in South America, would have been
greater also in these periods. The glacioeustatic movements would have been smaller during the Pliocene, with
a smaller exposure of the present submarine platform, a
more reduced climatic continentalization and less
extreme climatic events.
Colder-than-today environmental conditions would have
been frequent only after ca. 2.6 Ma ago. Before 3 Ma,
climatic conditions would have been warmer than even the
last interglacial periods, that is, the Holocene, MIS 5 and
MIS 7, with possible exceptions at 3.12, 3.3, 3.35, 4.8–4.9
and 5.7–5.8 Ma, according to the Southern Ocean 18O record.
The environmental and biogeographical changes that
took place during the LG and the last Termination would
have taken place at least 15 times during the last 1 Myr,
since the GPG. Perhaps with smaller intensity, they could
have occurred up to 100 times since the beginning of the
Pliocene. The ecological consequences of such climatic
changes are hard to quantify, but they must have been
highly significant. They should not be ruled out when
studying the Late Cenozoic biogeography, paleontology
and paleoenvironments of the Pampas and similar areas
of Uruguay and southern Brazil.
Much more is known today compared with what had
been proved only three decades ago. See, for instance,
Mercer (1976), or the discussion during the INQUA ‘‘Till
Commision’’ Patagonian Regional Meeting in March–
April 1982 (Rabassa, 1983; Fig. 45), or even the summary in Rabassa and Clapperton (1990).
Fig. 45. Group photo of the participants of the ‘‘INQUA
Till Commission South American Regional Meeting’’, San
Carlos de Bariloche, Argentina, during postmeeting
fieldtrip in front of Castaño Overo Glacier, Monte
Tronador (Fig. 1b, Site 12; photo taken by a fieldtrip
assistant in April 1982). The author is accompanied by
several then graduate students (Andrés Meglioli, Andrea
Coronato and Elizabeth Mazzoni among them) and many
distinguished visitors, Cal Heusser, Linda Heusser, Ernest
H. Muller, Art Bloom, Gerry Richmond, Trevor Chinn,
Dirk van Husen, Robert Vivian, Jan Lundqvist, Edward
Evenson and Friedrich Röthlisberger, among others.
Els AMS
LPCT
00008
196
22-1-2008
14:06
Page:196
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Much has to be done yet, but the construction of the
Patagonian glacial chronology, the best land-based glacial
record of the temperate zones of the Southern Hemisphere
and one of the most complete in the entire world has slowly
but steadily developed. This has been possible, thanks to the
efforts of many Argentinian and foreign scientists who have
challenged the huge Patagonian distances, loneliness and
emptyness, lack of logistics, roads or services, just as the
great Carl C:zon Caldenius did 75 yrs ago.
Much future work is needed to extend and consolidate
this chronology, which will provide a firm base for correlation with glacial and paleoclimate records elsewhere
in the world.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
Acknowledgments
16
17
The author wants to dedicate this chapter to the memory of
Dr Carl C:zon Caldenius, on the 75th anniversary of the
publication of his paramount work. The author is deeply
grateful to Dr John Mercer, who kindly introduced him to
the problem of ancient Patagonian tills in 1972, and Professor Francisco Fidalgo (Universidad de La Plata), who
generously cosupervised his doctoral dissertation in 1974
and provided him with the basic concepts and methodology
for the study and correlation of Patagonian glaciations.
Professor Félix González Bonorino (Fundación Bariloche),
who was the main advisor of his dissertation, oriented him
in the study of past and present glacigenic sediments.
The author also wants to thank all those colleagues
and graduate students who over the last 30 yrs have
generously educated him or kindly worked with him on
the study of Patagonian glaciations: Calvin J. Heusser
(deceased), Linda Heusser, Sigfrido Rubulis (deceased),
Jorge Suarez (deceased), Edward B. Evenson, Stephen C.
Porter, Andrés Meglioli, Luis Bertani, Aldo Brandani,
Daniel Cobos, José Boninsegna, Fidel Roig Junyent,
Ricardo Villalba, Guida Aliotta, Gunnar Schlieder,
George Stephens, Jim Clinch, David Serrat, Carles
Martı́, Jaap van der Meer, Kenneth Kodama, Donald
Easterbrook, Chalmers Clapperton, David Sugden, Nick
Hulton, Bradley Singer, Thao Ton-That, Dave Mickelson,
Mike Kaplan, James Bockheim, Matti Seppälä, Andrea
Coronato, Claudio Roig, Juan Federico Ponce, Oscar
Martı́nez, Mónica Salemme, Elizabeth Mazzoni and
Bettina Ercolano, among many others.
Dr Bradley Singer (Department of Geology and Geophysics, University of Wisconsin at Madison, USA),
Dr Robert Ackert (Harvard University, USA) and Dr
Michel Kaplan (Lamont-Doherty Geological Observatory,
USA), generously provided published information and
unpublished radiometric and cosmogenic data to support
the interpretations of this work.
The author is greatly indebted to Professor Jaap van der
Meer for his careful and dedicated review of a first draft of
the manuscript, thus certainly improving this chapter.
This chapter is the result of more than 30 yrs of fieldwork in different Patagonian regions and lab work at
CADIC-CONICET (Ushuaia), Fundación Bariloche (San
Carlos de Bariloche), Universidad Nacional del Comahue
(Neuquén) and other organizations. These investigations
were funded by many grants from CONICET, Agencia
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Nacional de Promoción Cientı́fica y Tecnológica
(ANPCYT, Argentina), Parques Nacionales (Argentina),
National Geographic Society (USA) and other institutions.
CONICET supported this work with Grant N 4305/97
and other more recent grants.
References
Ackert, R.P., Singer, B., Guillou, H. and Kurz, M. (1998).
Cosmogenic 3He production rates over the last 125,000
years: calibration against 40Ar/39Ar and unspiked K-Ar
ages of lava flows. Geological Society of America, 1998
Annual Meeting, Symposium 24, Abstracts, Toronto.
Adriasola, A.C., Tomson, S.N., Brix, M.R. et al. (2005).
Postmagmatic cooling and late Cenozoic denudation of
the North Patagonian Batholith in the Los Lagos
Region of Chile (41–42150 S). International Journal
of Earth Sciences (Geologische Rundschau), DOI
10.1007/s00531-005-0027-9.
Alberdi, M.T., Leone, G. and Tonni, E.P. (eds) (1995).
Evolución biológica y climática de la Región Pampeana durante los últimos cinco millones de años.
Monografı́as, Museo Nacional de Ciencias Naturales,
Madrid, 423 pp.
Ameghino, F. (1889). Contribución al conocimiento de
los mamı́feros fósiles de la República Argentina. Actas
Academia Nacional de Ciencias de Córdoba 6, 1–1027.
Córdoba, Argentina.
Amos, A.J. (1998). CADINCUA, Reunión de Campo, San
Carlos de Bariloche. Parte II. PROGEBA, San Carlos
de Bariloche.
Aniya, M. (1995). Holocene glacial chronology in Patagonia: Tyndall and Upsala glaciers. Arctic and Alpine
Research 27, 311–322.
Aniya, M. (1999). Recent glacier variations of the Hielos
Patagonicos, South America, and their contribution to
sea level change. Arctic, Antarctic and Alpine Research
21, 165–173.
Aniya, M., Sato, H., Naruse, R. et al. (1997). Recent
glacier variations in the Southern Patagonian Ice
Field, South America. Arctic and Alpine Research 29,
1–12.
Ardolino, A., Franchi, M., Remersal, M. and Salani, F.
(1999). El volcanismo en la Patagonia Extraandina. In:
Haller, M.J. (ed.), ‘‘Geologı́a Argentina’’, Anales
SEGEMAR 29. Buenos Aires, 579–612.
Ariztegui, D., Bianchi, M.M., Masaferro, J. et al. (1997).
Interhemispheric synchrony of late-glacial climatic
instability as recorded in proglacial Lake Mascardi,
Argentina. Journal of Quaternary Science 12, 333–338.
Auer, V. (1956). The Pleistocene of Fuego-Patagonia.
Part I: the ice and interglacial ages. Annales Academia
Scientiarum Fennicae, A, III, 45, 1–222.
Part II: The history of flora and vegetation. Annales
Academia Scientiarum Fennicae, A, III, 50, 1–239.
Part 3: Shoreline displacements. Annales Academia
Scientiarum Fennicae, A, III, 60, 1–247.
Part V: Quaternary problems of southern South
Els AMS
LPCT
00008
22-1-2008
14:06
Page:197
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
01
02
03
04
05
06
07
08
09
10
11
12
13
14
AU21
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
America. Annales Academia Scientiarum Fennicae, A,
III, 100, 1–60.
Balco, G., Rovey, C.W. II and Stone, J. (2005). The first
glacial maximum in North America. Science 307, 222.
Barendregt, R. and Duk-Rodkin, A. (2004). Chronology
and extent of Late Cenozoic ice sheets in North America:
A magnetostratigraphic assessment. In: Ehlers, J. and
Gibbard, P., (eds), Quaternary Glaciations – Extent and
Chronology, Part II: North America. Elsevier, Amsterdam. Developments in Quaternary Science 2, 1–7.
Becker, R.A., Ackert, R., Singer, B. et al. (2005). 10Be
and 36Cl surface exposure age of the Puerto Bandera
Moraine, Lago Argentino, 50 S. Geological Society of
America, Abstracts with Programs.
Benn, D. and Clapperton, C. (2000a). Glacial sediment –
landform associations and paleoclimate during the last
glaciation, Strait of Magellan, Chile. Quaternary
Research 54, 13–23.
Benn, D. and Clapperton, C. (2000b). Pleistocene glacitectonic landforms and sediments around Central
Magellan Strait, southernmost Chile: Evidence for fast
outlet glaciers with cold-based margins. Quaternary
Science Reviews 19, 591–612.
Bennett, K., Haberle, S. and Lumley, S. (2000). The Last
Glacial-Holocene transition in Southern Chile. Science
290, 325–327.
Bentley, M. and McCulloch, R. (2005). Impact of neotectonics on the record of glacier and sea level fluctuations, Strait of Magellan, Southern Chile. Geografiska
Annaler 87 A, 393–402.
Bentley, M., Sugden, D., Hulton, N. and McCulloch, R.
(2005). The landforms and pattern of deglaciation in the
Strait of Magellan and Bahı́a Inútil, Southernmost
South America. Geografiska Annaler 87 A, 313–333.
Berger, A. and Loutre, M.F. (1991). Insolation values for
the Climate of the last 10 Million years. Quaternary
Science Reviews 10, 297–318.
Bertani, L., Brandani, A. and Rabassa, J. (1986). Fluctuations of Castaño Overo Glacier in Northern Patagonia
since the beginning of the XVII century. Data of Glaciological Studies 57, 192–196. Moscow.
Blisniuk, P., Stern, L., Chamberlain, C.P. et al. (2006).
Climatic and ecologic changes during Miocene surface
uplift in the Southern Patagonian Andes. Backbone of
the Americas – Patagonia to Alaska Symposium, (3–7
April 2006), Paper 13–6, Abstracts, Geological Society
of America.
Blunier, T. and Brook, E. (2001). Timing of millennialscale climate change in Antarctica and Greenland during the last glacial period. Science 291, 109–111.
Blunier, T., Chappellaz, J., Schwander, J. et al. (1998).
Asynchrony of Antarctic and Greenland climate change
during the last glacial period. Nature 394, 739–743.
Brandani, A., Rabassa, J., Boninsegna, J. and Cobos, D.
(1986). Glacier fluctuations during and since the Little
Ice Age and forest colonization: Monte Tronador and
Volcan Lanin, Northern Patagonian Andes. Data of
Glaciological Studies 57, 196–206. Moscow.
Bruno, L.A., Baur, H., Graf, T. et al. (1997). Dating of
Sirius Group tillites in the Antarctic Dry Valleys with
cosmogenic 3 He and 21Ne. Earth and Planetary
Science Letters 147, 37–54.
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
197
Bujalesky, G.G., Heusser, C.J., Coronato, A.M.J. et al.
(1997). Pleistocene glaciolacustrine sedimentation at
Lago Fagnano, Andes of Tierra del Fuego, Southernmost South America. Quaternary Science Reviews 16,
767–778.
Busteros, A. and Lapido, O. (1983). Rocas básicas en la
vertiente noroccidental de la meseta del Lago Buenos
Aires, provincia de Santa Cruz. Asociación Geológica
Argentina, Revista 38, 427–436. Buenos Aires.
Caldenius, C. (1932). Las glaciaciones cuaternarias en
Patagonia y Tierra del Fuego. Geografiska Annaler 14,
1–164. Also published in Dirección General de Geologı́a y Minerı́a, Anales 95, 1–150. Buenos Aires.
Caldenius, C. (1940). The Tehuelche or Patagonian shingle formation. A contribution to the study of its origin.
Geografiska Annaler 22, 160–181.
Casassa, G. (1995). Glacier inventory in Chile: current
status and recent glacier variations. Annals of Glaciology 21, 317–322.
Casassa, G., Sepúlveda, F.V. and Sinclair, R.M. (ed)s
(2002a). The Patagonian Icefields. Kluwer Academic/
Plenum Publishers, New York, 192 pp.
Casassa, G., Smith, K., Rivera, A. et al. (2002b). Inventory of glaciers in Isla Riesco, Patagonia, Chile, based
on aerial photography and satellite imagery. Annals of
Glaciology 34, 373–378.
Casassa, G., Rivera, A., Escobar, F. et al. (2003). Snow
line rise in central Chile in recent decades and its
correlation with climate. EGS–AGU–EUG Joint Assembly, Abstracts, Nice, France, 6–11 April 2003, Abstract
#14395.
Cerling, T. and Harris, J. (1999). Carbon isotope fractionation between diet and bioapatite in ungulate mammals and
implications for ecological and paleoecological studies.
Oecologia 120, 347–363.
Cerling, T., Harris, J., MacFadden, B.J. et al. (1997).
Global vegetation change during the Miocene-Pliocene
boundary. Nature 389, 153–158.
Ciesielki, P., Ledbetter, M.T. and Elwood, B.B. (1982).
The development of Antarctic Glaciation and the Neogene palaeoenvironment of the Maurice Ewing Bank.
Marine Geology 46, 1–51.
Cione, A.L. and Tonni, E.P. (1999). Biostratigraphy and
chronological scale of uppermost Cenozoic in the Pampean Area, Argentina. In: Tonni, E.P. and Cione, A.L.
(eds), ‘‘Quaternary Vertebrate Paleontology in South
America’’. Quaternary of South America & Antarctic
Peninsula 12. A.A.Balkema Publishers, Rotterdam, 23–51.
Clapperton, C. (1971). Evidence of cirque glaciation in the
Falkland Islands. Journal of Glaciology 10, 121–125.
Clapperton, C. (1983). Nature of environmental changes in
South America at the last glacial maximum. Palaeogeography, Palaeoclimatology, Palaeoecology 101, 189–208.
Clapperton, C. (1989). Asymmetrical drumlins in Patagonia, Chile. Sedimentary Geology 62, 387–398.
Clapperton, C. (1990). Quaternary glaciations in the
Southern Ocean and Antarctic Peninsula area. Quaternary Science Reviews 9, 229–252.
Clapperton, C. (1993). Quaternary Geology and Geomorphology of South America. Elsevier, Amsterdam.
Clapperton, C. (2000). Interhemispheric synchroneity of
Marine Oxygen Isotope Stage 2 glacier fluctuations
Els AMS
LPCT
00008
198
22-1-2008
14:06
Page:198
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
along the American cordilleras transect. Journal of
Quaternary Science 15, 435–468.
Clapperton, C. and Roberts, D.E. (1986). Quaternary sea
level changes in the Falkland Islands. Quaternary of
South America and Antarctic Peninsula 4. A.A. Balkema Publishers, Rotterdam, 99–117.
Clapperton, C. and Sugden, D. (1976). The maximum
extent of glaciers in part of West Falkland. Journal of
Glaciology 17, 73–77.
Clapperton, C. and Sugden, D. (1989). Holocene glacier
fluctuations in South America and Antarctica. Quaternary Science Reviews 7, 185–198.
Clapperton, C., Sugden, D., Kaufman, D. and McCulloch, R.
(1995). The Late Glaciation in central Magellan
Strait, southernmost Chile. Quaternary Research 44,
133–148.
Coronato, A.M.J. (1990). Definición y alcance de la
última glaciación pleistocena (Glaciación Moat) en el
Valle de Andorra, Tierra del Fuego. XI Congreso
Geológico Argentino, Actas 1, 286–289. Buenos Aires.
Coronato, A.M.J. (1991). Cuerpos glacilacustres en la
deglaciación del Holoceno temprano en valles de los
Andes Fueguinos. Biologı́a Acuática 15, 16–17. Buenos
Aires.
Coronato, A.M.J. (1993). La Glaciación Moat (Pleistoceno superior) en los valles Pipo y Cañadón del Toro,
Andes Fueguinos. XII Congreso Geológico Argentino,
Actas 6, 40–47. Buenos Aires.
Coronato, A.M.J. (1995a). Geomorfologı́a glacial de
vales de los Andes Fueguinos y condicionantes fı́sicos
para la ocupación humana. Unpublished PhD Thesis,
Universidad de Buenos Aires, Facultad de Filosofı́a y
Letras, 317 pp. Buenos Aires.
Coronato, A.M.J. (1995b). The last Pleistocene glaciation
in tributary valleys of the Beagle Channel, Southernmost South America. Quaternary of South America &
Antarctic Peninsula 9. A.A. Balkema Publishers, Rotterdam, 173–182.
Coronato, A.M.J., Bujalesky, G., Pérez Alberti, A. and
Rabassa, J. (2004c). Evidencias criogénicas fósiles en
depósitos marinos interglaciarios de Tierra del Fuego,
Argentina. X Reunión Argentina de Sedimentologı́a,
Resúmenes, 48–49. San Luis, Argentina.
Coronato, A.M.J., Martı́nez, O. and Rabassa, J. (2004a).
Glaciations in argentine patagonia, Southern South
America. In: Ehlers, J. and Gibbard, P. (eds), Quaternary Glaciations: Extent and chronology. Part III: South
America, Asia, Africa, Australia and Antarctica.
Elsevier, Amsterdam, Developments in Quaternary
Science 2, 49–66.
Coronato, A.M.J., Meglioli, A. and Rabassa, J. (2004b).
Glaciations in the Magellan Straits and Tierra del
Fuego, Southernmost South America. In: Ehlers, J.
and Gibbard, P. (eds), Quaternary Glaciations: Extent
and chronology. Part III: South America, Asia, Africa,
Australia and Antarctica. Elsevier, Amsterdam, Developments in Quaternary Sciences 2, 45–48.
Coronato, A.M.J., Salemme, M. and Rabassa, J. (1999).
Paleoenvironmental conditions during the early peopling of Southernmost South America (Late GlacialEarly Holocene, 14–8 ka BP). Quaternary International
53/54, 77–92.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Coronato, A.M.J., Seppälä, M. and Rabassa, J. (2005).
Last Glaciation landforms in Lake Fagnano ice lobe,
Tierra del Fuego, Southernmost Argentina. VI International Conference in Geomorphology, S1 (Glacial and
periglacial geomorphology), Abstracts, Zaragoza,
Spain, September 2005.
Coudrian, A., Francou, B. and Kundzewicz, Z. (2005).
Glacier shrinkage in the Andes and consequences for
water resources – Editorial. Hydrological Sciences
Journal 50, 6, 925–932.
Czajka, W. (1955). Rezente und Pleistozäne Verbreitung
und Typen des periglazialen Denudiationszyklus in
Argentinien. Societas Geographica Fennicae, Acta
Geographica 14, 121–140.
Darwin, C. (1842). On the distribution of erratic boulders
and on the contemporaneous unstratified deposits of
South America. Transactions Geological Society
London, 2nd. Series, 6, 415–431.
Darwin, C. (1846). On the geology of the Falkland
Islands. Quarterly Journal of the Geological Society
of London 2, 267–274.
De Geer, G. (1927). Late Glacial clay varves in Argentina, measured by Dr Carl Caldenius, dated and connected with solar curve through the Swedish timescale.
Geografiska Annaler 9, 1–8.
deMenocal, P.B. and Bloemendal, J. (1995). PlioPleistocene climatic variability in subtropical Africa
and the paleoenvironment of hominid evolution: a combined data-model approach. In: Vrba, E.S., Denton,
G.H., Partridge, T.C. and Burckle, L.H. (eds), Paleoclimate and Evolution, with Emphasis on Human Origins.
Yale University Press, New Haven and London, 262–288.
Denton, G., Heusser, C.J., Lowell, T. et al. (1999a).
Interhemispheric linkage of paleoclimate during the
last glaciation. Geografiska Annaler 81 A, 107–154.
Denton, G., Lowell, T., Heusser, C.J. et al. (1999b).
Geomorphology, stratigraphy and radiocarbon chronology of Llanquihue Drift in the area of the Southern
Lake District, Seno Reloncavı́, and Isla de Chiloé,
Chile. Geografiska Annaler 81 A, 167–229.
Dessanti, R. (1972). Andes Patagónicos septentrionales.
In: Leanza, A. (ed.), ‘‘Geologı́a Regional Argentina’’,
Academia Nacional de Ciencias de Córdoba, 655–688.
Dillon, A. and Rabassa, J. (1985). Miembro La
Chumbiada, Formación Luján (Pleistoceno, provincia
de Buenos Aires): una nueva unidad litoestratigráfica
del valle del Rı́o Salado. I Jornadas Geológicas
Geofı́sicas Bonaerenses, Actas, Resúmenes 27. Tandil,
Argentina.
Douglass, D. and Bockheim, J. (2006). Soil-forming rates
and processes on Quaternary moraines near Lago Buenos
Aires, Argentina. Quaternary Research 65, 293–307.
Douglass, D., Singer, B., Kaplan, M. et al. (2005). Evidence of early Holocene glacial advances in southern
South America from cosmogenic surface-exposure dating. Geology 33, 237–240.
Duk-Rodkin, A., Barendregt, R., Froese, D. et al. (2004).
Timing and extent of Plio-Pleistocene glaciations in
north-western Canada and east-central Alaska. In:
Ehlers, J. and Gibbard, P. (eds), Quaternary Glaciations – Extent and Chronology, Part II: North America.
Els AMS
LPCT
00008
22-1-2008
14:06
Page:199
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Elsevier, Amsterdam, Developments in Quaternary
Science 2, 313–346.
Ercolano, B., Mazzoni, M., Vazquez, M. and Rabassa, J.
(2004). Drumlins y formas drumlinoides del Pleistoceno inferior en Patagonia Austral, Provincia de Santa
Cruz. Asociación Geológica Argentina, Revista 59, 4,
771–777. Buenos Aires.
Feruglio, E. (1944). Estudios geológicos y glaciológicos
en la región del Lago Argentino (Patagonia). Boletı́n
Academia Nacional Ciencias de Córdoba 37, 1–208.
Feruglio, E. (1950). Descripción Geológica de la Patagonia. YPF, 3, 1–393. Buenos Aires.
Fidalgo, F. and Riggi, J.C. (1965). Los rodados patagónicos en la Meseta del Guenguel y alrededores (Santa
Cruz). Asociación Geológica Argentina, Revista 25,
430–443. Buenos Aires.
Fidalgo, F., De Francesco, F.O. and Pascual, R. (1975).
Geologı́a superficial de la llanura bonaerense. Relatorio
Geologı́a Provincia de Buenos Aires, VI Congreso Geológico Argentino 103–138. Buenos Aires.
Fleck, R.J., Mercer, J.H., Nairn, A.E.M. and Peterson, D.N.
(1972). Chronology of Late Pliocene and Early Pleistocene
glacial and magnetic events in southern Argentina. Earth
Planetary Science Letters 16, 15–22.
Flint, R.F. and Fidalgo, F. (1964). Glacial Geology of the
east flank of the Argentine Andes between latitude
39100 S and latitude 41210 S. Geological Society of
America Bulletin 75, 335–352.
Flint, R.F. and Fidalgo, F. (1969). Glacial Drift in the
Eastern Argentine Andes between latitude 41100 S and
latitude 43210 S. Geological Society of America Bulletin 80, 1043–1052.
Fogwill, C. and Kubik, P. (2005). A glacial stage spanning the Antarctic Cold Reversal in Torres del Paine
(51 S), Chile, based on preliminary cosmogenic exposure ages. Geografiska Annaler 87 A, 403–408.
Gaiero, D., Depetris, P., Probst, J.-L. et al. (2004). The
signature of river- and wind-borne materials exported
from Patagonia to the southern latitudes: a view from
REEs and implications for paleoclimatic studies. Earth
and Planetary Sciences 219, 357–376.
Glasser, N.F., Harrison, S., Winchester, V. and Aniya, M.
(2004). Late Pleistocene and Holocene palaeoclimate
and glacier fluctuations in Patagonia. Global and
Planetary Change 43, 79–101.
González Bonorino, F. (1944). Descripción geológica y
petrográfica de la Hoja 41b, Rı́o Foyel, Rı́o Negro.
Dirección de Minas, Geologı́a e Hidrogeologı́a, Boletı́n
56. Buenos Aires.
González Bonorino, F. (1973). Geologı́a del área entre
San Carlos de Bariloche y Llao-Llao, provincia de Rı́o
Negro. Fundación Bariloche, Publicaciones Departamento Recursos Naturales y Energı́a 16, San Carlos de
Bariloche, Argentina.
González Dı́az, E.F. (1993a). Nuevas determinaciones y
mayores precisiones en las localizaciones de los términos glaciarios del ‘‘Inicio’’ y ‘‘Daniglacial’’ en el
sector de Cushamen (Noroeste del Chubut). XII Congreso Geológico Argentino & II Congreso de
Exploración de Hidrocarburos, Actas 6, 48–55. Buenos Aires.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
199
González Dı́az, E.F. (1993b). Mapa geomorfológico del
sector de Cushamen (NO de Chubut): interpretación
genética y secuencial de sus principales geoformas.
XII Congreso Geológico Argentino and II Congreso de
Exploración de Hidrocarburos, Actas 6, 56–65. Buenos
Aires.
González Dı́az, E.F. (2003). El englazamiento en la
región de la caldera de Caviahue-Copahue (Provincia
del Neuquén): Su reinterpretación. Asociación Geológica Argentina, Revista 58, 356–366. Buenos Aires.
González Dı́az, E.F. and Andrada de Palomera, R.
(1995). Los sistemas de morenas terminales de Caldenius al sur de la localidad de Ñorquinco, sudoeste de la
provincia de Rı́o Negro. Asociación Geológica Argentina, Revista 50, 212–218. Buenos Aires.
González Dı́az, E.F. and Nullo, F.E. (1980). Cordillera
Neuquina. In: Leanza, A. (ed.), Geologı́a Regional
Argentina 2. Academia Nacional Ciencias de Córdoba,
Córdoba, Argentina, 1099–1148.
González Dı́az, E.F., Riggi, J.C. and Fauqué, L. (1986).
Formación Caleufu (nov.nom.): reinterpretación de las
formaciones Rı́o Negro y Alicurá, en el área de Collón
Curá, sur del Neuquén. Asociación Geológica Argentina, Revista 41, 81–105. Buenos Aires.
Gordillo, S., Coronato, A. and Rabassa, J. (1993). Late
Quaternary evolution of a subantarctic paleofjord, Tierra
del Fuego. Quaternary Science Reviews 12, 889–897.
Gracia, R. (1958). Informe geológico de las cartas Paso
Flores y Traful. Secretarı́a de Ejército, Dirección General Ingenieros, Buenos Aires, unpublished report.
Greco, R. (1975). Descripción geológica de la Hoja 40a,
Cerro Tronador. Servicio Geológico Nacional, Buenos
Aires, unpublished report.
Groeber, P.F. (1936). Oscilaciones del clima en la Argentina desde el Plioceno. Revista Centro Estudiantes
Ciencias Naturales (CECN) 1, 1–9. Buenos Aires.
Groeber, P.F. (1952). Glacial Tardı́o y postglacial en Patagonia. Revista Museo Municipal de Ciencias Naturales y
Tradicionales de Mar del Plata 1. Mar del Plata.
Guillou, H. and Singer, B. (1997). Combined unspiked
K-Ar and 40Ar/39Ar dating of Late Quaternary lavas.
EOS Transactions of the American Geophysical Union,
Abstracts, 1997 Fall Meeting, 78, 771.
Hajdas, I., Bonani, G., Moreno, P. and Ariztegui, D.
(2003). Precise radiocarbon dating of Late-Glacial
cooling in mid-latitude South America. Quaternary
Halle, T.G. (1910). On Quaternary deposits and changes
of levels in Patagonia and Tierra del Fuego. Bulletin
Geological Institution University of Upsala 9, 93–117.
Harris, S. (2005). Thermal history of the Arctic Ocean environs adjacent to North America during the last 3.5 Ma
and a possible mechanism for the cause of the cold events
(major glaciations and permafrost events). Progress in
Physical Geography 29, 1–19.
Heusser, C.J. (1960). Late Pleistocene environments of
the Laguna San Rafael area, Chile. Geographical
Review 50, 555–577.
Heusser C.J. (1964). Some pollen profiles from the Laguna
de San Rafael area, Chile. In: Cranwell, L.M. (ed.),
Ancient Pacific Floras. The Pollen Story. University of
Hawaii Press, Honolulu, 95–114.
Els AMS
LPCT
00008
200
22-1-2008
14:06
Page:200
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Heusser, C.J. (1974). Vegetation and climate of the
southern Chilean lake district during and since the
Last Interglaciation. Quaternary Research 4, 290–315.
Heusser, C.J. (1984). Late Quaternary climates in Chile.
In: Vogel, J.C. (ed.), Late Cainozoic Paleoclimates of
the Southern Hemisphere. A.A. Balkema Publishers,
Rotterdam, 59–83.
Heusser, C.J. (1987). Quaternary vegetation of Southern
South America. Quaternary of South America & Antarctic Peninsula 5. A.A. Balkema Publishers, Rotterdam, 197–221.
Heusser, C.J. (1989a). Late Quaternary vegetation and
climate of Southern Tierra del Fuego. Quaternary
Research 31, 396–406.
Heusser, C.J. (1989b). Polar perspective of Late Quaternary climates in the Southern Hemisphere. Quaternary
Heusser, C.J. (1993). Late-Glacial of Southern South
America. Quaternary Science Reviews 12, 345–350.
Heusser, C.J. (1998). Deglacial palaeoclimate of the
American sector of the Southern Ocean: Late GlacialHolocene records from the latitude of Canal Beagle
(55 S), Argentine Tierra del Fuego. Palaeogeography,
Palaeoclimatology, Palaeoecology 141, 277–301.
Heusser, C.J. (2003). Ice Age Southern Andes. Elsevier,
Amsterdam. Developments in Quaternary Sciences 3.
Heusser, C.J. and Flint, R.F. (1977). Quaternary glaciations and environments of northern Isla de Chiloé,
Chile. Geology 5, 305–308.
Heusser, C.J. and Rabassa, J. (1987). Cold climate episode of Younger Dryas age in Tierra del Fuego. Nature
328, 609–611.
Heusser, C.J. and Streeter, S. (1980). A temperature and
precipitation record of the past 16,000 years in Southern
Chile. Science 210, 1345–1347.
Heusser, C.J., Streeter, S. and Stuiver, M. (1981). Temperature and precipitation record in Southern Chile
extended 43,000 years ago. Nature 294, 65–67.
Heusser, C., Heusser, L., Lowell, T. et al. (2000). Deglacial palaeoclimate at Puerto del Hambre, Subantarctic
Patagonia, Chile. Journal of Quaternary Science 15,
101–114.
Hoganson, J.W. and Ashworth, A.C. (1992). Fossil beetle
evidence for climatic change 18,000–10,000 years BP
in South-Central Chile. Quaternary Research 37,
101–116.
Hubbard, A., Hein, A., Kaplan, M. et al. (2005). A
modeling reconstruction of the last glacial maximum
ice sheet and its deglaciation in the vicinity of the
Northern Patagonian Icefield, South America. Geografiska Annaler 87 A, 375–391.
Hulton, N., Purves, N., McCulloch, R. et al. (2002). The
Last Glacial Maximum and deglaciation in southern South
America. Quaternary Science Reviews 21, 233–241.
Imbrie, J. and Imbrie, K. (1979). Ice Ages: Solving the
Mystery. The MacMillan Press, London.
Iriondo, M. (1999). Climatic changes in the South American plains. Quaternary International 57/58, 93–122.
Isla, F.I. and Schnack, E. (1995). Submerged moraines
offshore northern Tierra del Fuego, Argentina. Quaternary of South America and Antarctic Peninsula 9.
A.A. Balkema Publishers, Rotterdam, 205–222.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Kaplan, M.R., Ackert, R.P., Jr, Singer, B.S. et al. (2004).
Cosmogenic nuclide chronology of millenial-scale glacial advances during O-isotope Stage 2 in Patagonia.
Geological Society of America Bulletin 116, 308–321.
Kaplan, M.R., Coronato, A., Hulton, N.R.J. et al. (2007).
Cosmogenic nuclide measurements in southernmost
South America and implications for landscape change.
Geomorphology 87, 284–301.
Kaplan, M.R., Douglass, D., Singer, B.S. et al. (2005).
Cosmogenic nuclide chronology of pre-glacial maximum moraines at Lago Buenos Aires, 46 S, Argentina.
Quaternary Research 64, 301–315.
Kaplan, M.R., Douglass, D., Singer, B.S. et al. (2006).
Response to Wenzens, G., 2006, comment on Kaplan
et al., 2005, Cosmogenic nuclide chronology of preglacial maximum moraines at Lago Buenos Aires,
46 S, Argentina. Quaternary Research 66, 367–369.
Kennett, J.P. (1995). A review of polar climatic evolution
during the Neogene, based on the marine sedimentary
record. In: Vrba, E.S., Denton, G.H., Partridge, T.C.
and Burckle, L.H. (eds), Paleoclimate and Evolution,
with Emphasis on Human Origins. Yale University
Press, New Haven and London, 49–64.
Kodama, K., Evenson, E.B., Clinch, J.M. and Rabassa, J.
(1985). Anomalous geomagnetic field behaviour
recorded by glacial sediments from Northwestern Patagonia, Argentina. Journal of Geomagnetics and Geoelectricity 37, 1035–1050.
Kodama, K., Rabassa, J., Evenson, E.B. and Clinch, J.M.
(1986). Paleomagnetismo y edad relativa del Drift
Pichileufu en su área tipo, San Carlos de Bariloche,
Rı́o Negro. Asociación Geológica Argentina, Revista
41, 1–2, 165–178. Buenos Aires.
Kranck, E. (1932). Geological investigations in the
Cordillera of Tierra del Fuego. Acta Geographica 4,
2, 1–131. Helsinki.
Lapido, O., Beltramone, C. and Haller, M.J. (1990). Glacial
deposits on the Patagonian cordillera at latitude 43300 S.
Quaternary of South America & Antarctic Peninsula 6.
Laugenie, C. (1984). Le dernier cycle glaciaire Quaternaire et la construction des nappes fluviatiles d’avant
pays dans les Andes Chiliennes. Bulletin Association
Franc˛aise d́Études du Quaternaire 1–3, 139–145.
Laugenie, C. and Mercer, J.H. (1973). Glacier in Chile
ended a major readvance 36,000 years ago: some global
comparisons. Science 183, 1017–1019.
Lowell, T., Heusser, C.J., Andersen, B. et al. (1995).
Interhemispheric correlation of Late Pleistocene glacial
events. Science 269, 1541–1549.
Lundqvist, J. (1983). Carl C:zon Caldenius and the Swedish
work on Quaternary geology in Argentina. Quaternary of
South America & Antarctic Peninsula 1. A.A. Balkema
Publishers, Rotterdam, 1–4.
Lundqvist, J. (1991). Carl C:zon Caldenius – geologist,
geotechnician, predecessor of IGCP. Boreas, Pioneer
Series 20, 183–189.
Lundqvist, J. (2001). Carl Caldenius och Patagoniens
glacialgeologi. In: Antarktanderna, Svensk forskning i
Otto Nordelkjölds fotspår, Ymer 121, 143–152.
Malagnino, E. (1995). The discovery of the oldest extraAndean glaciation in the Lago Buenos Aires Basin,
Els AMS
LPCT
00008
22-1-2008
14:06
Page:201
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Argentina. Quaternary of South America & Antarctic
Peninsula 9. A.A. Balkema Publishers, Rotterdam, 69–83.
Marden, C. (1994). Factors Affecting the Volume of
Quaternary Glacial Deposits in Southern Patagonia.
Geografiska Annaler 76A, 261–269.
Marden, C. (1997). Late-glacial fluctuations of South
Patagonian Icefield, Torres del Paine National Park,
southern Chile. Quaternary International 38/39, 61–68.
Markgraf, V. (1991). Younger Dryas in southern South
America? Boreas 20, 63–69.
Markgraf, V. (1993). Younger Dryas in southernmost
South America – an update. Quaternary Science
Reviews 12, 351–355.
Martı́nez, O.A. (2002). Geomorfologı́a y geologı́a de los
depósitos glaciarios y periglaciarios de la región comprendida entre los 43 y 44 lat. sur., Chubut, Argentina. Unpublished PhD Dissertation, Universidad
Nacional de la Patagonia-San Juan Bosco. Comodoro
Rivadavia, Argentina.
McCulloch, R., Bentley, M., Purves, S. et al. (2000).
Climatic inferences from glacial and palaeoecological
evidence at the last glacial termination, southern South
America. Journal of Quaternary Science 15, 409–417.
McCulloch, R., Clapperton, C., Rabassa, J. and Currant,
A. (1997). The natural setting : The glacial and postglacial environmental history of Fuego-Patagonia. In:
McEwan, C., Borrero, L. and Prieto, A. (eds), London,
The British Museum Press, Patagonia, 12–31.
McCulloch, R. and Davies, S. (2001). Late glacial and
Holocene paleoenvironmental
change in the central Strait of Magellan, southern Patagonia. Palaeogeography, Palaeoclimatology, Palaeoecology 173, 143–173.
McCulloch, R., Fogwill, C., Sugden, D. et al. (2005).
Chronology of the Last Glaciation in central Strait
of Magellan and Bahı́a Inútil, southernmost South
America. Geografiska Annaler 87 A, 289–312.
Meglioli, A. (1992). Glacial Geology of Southernmost
Patagonia, the Strait of Magellan and Northern Tierra
del Fuego. Unpublished PhD Dissertation, Lehigh
University, Bethlehem, Pennsylvania, USA.
Meglioli, A., Evenson, E., Zeitler, P. and Rabassa, J.
(1990). Cronologı́a absoluta y relativa de los depósitos
glaciarios de Tierra del Fuego, Argentina y Chile.
XI Congreso Geológico Argentino, Actas 2, 457–460.
Buenos Aires, San Juan.
Mercer, J.H. (1965). Glacier variations in southern Patagonia. Geographical Review 55, 390–413.
Mercer, J.H. (1968). Variations of some Patagonian glaciers since the Late-Glacial. American Journal of
Science 266, 91–109.
Mercer, J.H. (1969). Glaciation in Southern Argentina
more than two million years ago. Science 164, 3881,
823–825.
Mercer, J.H. (1970). Variations of some Patagonian glaciers since the Late-Glacial: II. American Journal of
Science 269, 1–25.
Mercer, J.H. (1972). Cainozoic temperature trends in the
Southern Hemisphere: Antarctic and Andean glacial
evidence. In: van Zinderen Bakker, E. (ed.), Palaeoecology of Africa, 8. A.A. Balkema Publishers,
Rotterdam, 85–114.
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
201
Mercer, J.H. (1976). Glacial history of Southernmost
South America. Quaternary Research 6, 125–166.
Mercer, J.H. (1982). Holocene glacier variations in
southern South America. Striae 18, 35–40.
Mercer, J.H. (1983). Cenozoic glaciation in the Southern
Hemisphere. Annual Review Earth Planetary Sciences
11, 99–132.
Mercer, J.H. and Sutter, J. (1981). Late Miocene-earliest
Pliocene glaciation in Southern Argentina: implications
for global ice-sheet history. Palaeogeography, Palaeoclimatology, Palaeoecology 38, 185–206.
Mercer, J.H., Fleck, R.J., Mankinen, E.A. and Sander, W.
(1975). Southern Patagonia: glacial events between 4
MY and 1 MY ago. In: Suggate, R.P. and Cresswell,
M.M. (eds), ‘‘Quaternary Studies’’, Royal Society New
Zealand Bulletin 13, 223–230.
Miotti, L. and Salemme, M. (1999). Biodiversity, taxonomic richness and specialists-generalists during the
Late Pleistocene/Early Holocene times in Pampean
Patagonia (Argentina, Southern South America). Quaternary International 53–54, 53–68.
Miró, R. (1967). Geologı́a glaciaria y preglaciaria del
valle de Epuyén. Asociación Geológica Argentina,
Revista 22, 177–202.
Moreno, F.P. (1897). Apuntes preliminares sobre una
excursión al Neuquén, Rı́o Negro, Chubut y Santa
Cruz. Editorial Elefante Blanco (ed. 1999), Buenos
Aires, 192 pp.
Mörner, N.A. and Sylwan, C. (1989). Magnetostratigraphy of the Patagonain moraine sequence at Lago Buenos Aires. Journal of South American Earth Sciences 2,
385–390.
Muhs, D.R. and Zárate, M. (2001). Late Quaternary
eolian records of the Americas and their paleoclimatic
significance. In: Markgraf, V. (ed.), Interhemispheric
climate linkages. Academic Press, New York, 183–216.
Muller, E. (1959). Glacial geology of the Laguna San
Rafael area, southern Chile. American Geographical
Society, Technical Report 2, 1–23.
Nabel, P., Cione, A.L. and Tonni, E.P. (2000). Environmental changes in the Pampean area of Argentina at the
Matuyama-Brunhes (C1r-C1n) Chrons boundary.
Palaeogeography, Palaeoclimatology, Palaeoecology
162, 403–412.
Naruse, R., Aniya, M., Skvarca, P. and Casassa, G.
(1995). Recent variations of calving glaciers in Patagonia, South America, revealed by ground surveys,
satellite-data analyses and numerical experiments.
Annals of Glaciology 21, 297–303.
Nordenskjöld, O. (1899). Geologie, Geographie und
Anthropologie. Schwedischen Expedition nach den Magellansländern, 1895–1897. Norstedt and Söner, Stockholm.
Opdyke, N.D. (1995). Mammalian migration and climate
over the last 7 Ma. In: Vrba, E.S., Denton, G.H., Partridge, T.C. and Burckle, L.H. (eds), Paleoclimate and
Evolution, with Emphasis on Human Origins. Yale
University Press, New Haven and London, 109–114.
Orgeira, M.J. (1990). Paleomagnetism of late Cenozoic
fossiliferous sediments from Barranca de los Lobos
(Buenos Aires Province, Argentina). The magnetic age
of the South American land-mammal ages. Physics of
the Earth and Planetary Interiors 64, 121–132.
Els AMS
LPCT
00008
202
01
02
03
04
05
06
AU22
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
22-1-2008
14:06
Page:202
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
Panhke, K., Zahn, R., Elderfield, H. and Schulz, M.
(2003). 340,000-year centennial scale marine record
of Southern Hemisphere climatic oscillations. Science
301, 948–952.
Pascual, R., Ortiz Jaureguizar, E. and Prado, J. (1996).
Land mammals: Paradigm for Cenozoic South American
Geobiotic Evolution. In: Arratia, G., (ed.), Münchner
Geowissenschaftliche Abhandlungen, A 30, 265–320.
Planas, X., Ponsa, A., Coronato, A.M. and Rabassa, J.
(2002). Geomorphological evidence of different glacial
stages in the Martial Cirque, Fuegian Andes, Southernmost South America. Quaternary International 87, 19–27
Polanski, J. (1965). The maximum glaciation in the
Argentine Cordillera. Geological Society of America,
Special Paper 84, 444–472.
Porter, S. (1981). Pleistocene glaciation in the southern
Lake District of Chile. Quaternary Research 16,
263–292.
Porter, S. (1989). Character and ages of Pleistocene drifts
in a transect across the Strait of Magellan. Quaternary of
Porter, S. (2000). Onset of Neoglaciation in the Southern
Hemisphere. Journal of Quaternary Science 15, 395–408.
Porter, S., Stuiver, M. and Heusser, C. (1984). Holocene
sea-level changes along the Strait of Magellan and
Beagle Channel, southernmost South America. Quaternary Research 22, 59–67.
Rabassa, J. (1975). Geologı́a de la Región de PilcaniyeuComallo, provincia de Rı́o Negro, Argentina. Unpublished PhD Thesis, Universidad Nacional de La Plata,
La Plata, and Fundación Bariloche, Departamento de
Recursos Naturales y Energı́a, Publicaciones 17,
1–128. San Carlos de Bariloche.
Rabassa, J. (1983). INQUA Commission on lithology and
genesis of Quaternary deposits: South American Regional
Meeting, Argentina, 1982. In: Evenson, E.B., Schlüchter,
C. and Rabassa, J. (eds), Tills and Related Deposits.
Rabassa, J. (1999). Cuaternario de la Cordillera Patagónica y Tierra del Fuego. In: Haller, M.J. (ed.), ‘‘Geologı́a Argentina’’, Anales SEGEMAR. Buenos Aires.
Rabassa, J. (2007). Global climate change and its impact
on the glaciers and permafrost of Patagonia, Tierra del
Fuego and the Antarctic Peninsula. São Paulo, Regional Meeting on Global Climatic Change, Proceedings,
University of São Paulo, digital publication.
Rabassa, J., Brandani, A., Boninsegna, J. and Cobos, D.
(1984). Cronologı́a de la ‘‘Pequeña Edad del Hielo’’ en
los glaciares Rı́o Manso y Castaño Overo, Cerro Tronador, Provincia de Rı́o Negro. IX Congreso Geológico
Argentino, Actas 3, 624–639. San Carlos de Bariloche.
Rabassa, J., Bujalesky, G., Meglioli, A. et al. (1992). The
Quaternary of Tierra del Fuego, Argentina: the status of
our knowledge. Sveriges Geologiska Undersökning,
Ser.Ca. 81, 249–256.
Rabassa, J. and Clapperton, C.M. (1990). Quaternary
Glaciations of the Southern Andes. Quaternary Science
Reviews 9, 153–174.
Rabassa, J. and Coronato, A.M.J. (2002). Glaciaciones
del Cenozoico Tardı́o. In: Haller, M.J. (ed.), ‘‘Geologı́a
y Recursos Naturales de Santa Cruz’’. XV Congreso
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Geológico Argentino, Relatorio 1, 19. El Calafate,
Argentina, 303–315.
Rabassa, J., Coronato, A. and Salemme, M. (2005).
Chronology of the Late Cenozoic Patagonian glaciations and their correlation with biostratigraphic units
of the Pampean region (Argentina). Journal of South
American Earth Sciences 20, 81–104.
Rabassa, J., Coronato. A.M., Bujalesky, G. et al. (2000).
Quaternary of Tierra del Fuego, southernmost South
America: an updated review. Quaternary International
68–71, 217–240.
Rabassa, J., Coronato, A.M., Roig, C. et al. (2004). Un
bosque sumergido en Bahı́a Sloggett, Tierra del Fuego,
Argentina: evidencia de actividad neotectónica diferencial en el Holoceno tardı́o. In: Blanco Chao, R., López
Bedoya, J. and Pérez Alberti, A. (eds), Procesos Geomorfológicos y evolución costera, II Reunión Geomorfologı́a Litoral, Actas. Santiago de Compostela, Spain,
333–345.
Rabassa, J. and Evenson, E.B. (1996). Reinterpretación
de la estratigrafı́a glaciaria de la región de San Carlos
de Bariloche. XIII Congreso Geológico Argentino,
Actas 4, 327. Buenos Aires.
Rabassa, J., Evenson, E.B. and Stephens, G.C. (1986).
Nuevas
evidencias
del
englazamiento
Plioceno-Pleistoceno inferior en los Andes Patagónicos
Septentrionales: Cerro Tronador, Rı́o Negro. Asociación Geológica Argentina, Revista 41, 405–409. Buenos Aires.
Rabassa, J., Evenson, E.B., Clich, J.M. et al. (1990a).
Geologı́a del Cuaternario del Valle del Rı́o Malleo,
Provincia del Neuquén. Asociación Geológica Argentina, Revista 45, 5–68. Buenos Aires.
Rabassa, J., Heusser, C. and Rutter, N. (1990b). LateGlacial and Holocene of Argentine Tierra del Fuego.
Quaternary of South America and Antarctic Peninsula
7, 327–351. A.A. Balkema Publishers, Rotterdam.
Rabassa, J., Roig, C., Singer, B. et al. (1996). Bloques
erráticos y rasgos periglaciales observados en el Cerro
del Fraile, Lago Argentino (Santa Cruz, Argentina).
XIII Congreso Geológico Argentino and III Congreso
Exploración Hidrocarburos, Actas 4, 345. Buenos
Aires.
Rabassa, J., Rubulis, S. and Suarez, J. (1978). Los glaciares del Monte Tronador. Anales de Parques Nacionales 14, 261–316. Buenos Aires.
Rabassa, J., Rubulis, S. and Brandani, A. (1980). East- AU23
west and north-south snow line gradients in the northern
Patagonian Andes, Argentina. World Glacier Inventory.
IAHS-AISH Publication 126, 1–10.
Rabassa, J., Rubulis, S. and Suarez, J. (1981). Moraine
in-transit as parent material for soil development and
the growth of Valdivian Rain Forest on moving ice:
Casa Pangue Glacier, Mount Tronador (lat. 41100 S),
Chile. Annals of Glaciology 2, 97–102.
Rabassa, J., Serrat, D., Marti, C. and Coronato, A.
(1990c). Internal structure of drumlins in Gable Island,
Beagle Channel, Tierra del Fuego, Argentina. LUNDQUA Report 32, 3–5. Lund.
Ramos, V. (1999a). Las provincias geológicas del territorio argentino. In: Haller, M.J. (ed.), ‘‘Geologı́a Argentina’’, Anales SEGEMAR 29, 41–96. Buenos Aires.
Els AMS
LPCT
00008
22-1-2008
14:06
Page:203
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Ramos, V. (1999b). Evolución tectónica de la Argentina.
In: Haller, M.J. (ed.), ‘‘Geologı́a Argentina’’, Anales
SEGEMAR 29, 715–759. Buenos Aires.
Rignot, E., Rivera, A. and Casassa, G. (2003). Contribution of the Patagonian Ice Fields of South America to
sealevel rise. Science 302, 434–437.
Rivera, A. and Casassa, G. (2004). Ice elevation, areal
and frontal changes of glaciers from National Park
Torres del Paine, Southern Patagonian Icefield. Arctic,
Antarctic and Alpine Research 36, 379–389.
Roberts, D.E. (1984). Quaternary history of the Falkland
Islands. Unpublished PhD Dissertation, University of
Aberdeen, Scotland.
Rosenbluth, B., Fuenzalida, H. and Aceituno, P. (1997).
Recent temperature variations in Southern South America. International Journal of Climatology 17, 65–85.
Röthlisberger, F. (1987). 10,000 Jahre Gletschergeschichte der Erde. Verlag Sauerlander, Aarau, 416.
Röthlisberger, F. and Geyh, M. (1985). Gletscherswankungen der Nacheiszeit in der Cordillera Blanca (Peru)
und den sudlichen Anden Chiles und Argentiniens.
Zentralblatt Geologie und Paläontologie 1, 11/12,
1611–1613.
Rovereto, G. (1912). Studi di geomorfologia argentina.
III, La valle del Rı́o Negro: 2. Il Lago Nahuel Huapi.
Bolletino della Societa Geologica Italiana 31, 181–237.
Ruddiman, W.F., McIntyre, A. and Raymo, M. (1986).
Matuyama 41,000 years cycles in North Atlantic Ocean
and Northern Hemisphere Ice Sheets. Earth & Planetary Science Letters 80, 117–129.
Rutter, N., Zhongli Ding and Tungsheng Liu (1991).
Comparison of isotope stages 1–61 with the Baojitype pedostratigraphic section of North-Central China.
Canadian Journal of Earth Sciences 28, 985–990.
Schellmann, G. (1998). Jungkänozoische Landschaftsgesschichte Patagoniens (Argentinien). Andine Vorlandvergletscherungen, Talentwicklung und marine
Terrasen. Essener Geographische Arbeiten 29, 1–218.
Schellmann, G. (1999). Landscape evolution and glacial
history of Southern Patagonia (Argentina) since the
Late Miocene – some general aspects. Zentralblatt Geologie und Paläontologie 1, 7/8, 1013–1026.
Schellmann, G. (2003). Südpatagonien: Gletschergeschichte
in einem Trockengebiet der südhemisphärischen Mittelbreiten. Geographische Rundschau 55, 22–27.
Schlieder, G. (1989). Glacial Geology of the Northern
Patagonian Andes between lakes Aluminé and Lácar.
Unpublished Ph.D. Dissertation, Lehigh University,
Bethlehem, Pennsylvania, USA.
Shackleton, N.J. (1995). New data on the evolution of
Pliocene climatic variability. In: Vrba, E.S., Denton,
G.H., Partridge, T.C. and Burckle, L.H. (eds), Paleoclimate and Evolution, with Emphasis on Human Origins.
Yale University Press, New Haven and London,
242–248.
Shackleton, N.J., Berger, A. and Peltier, W. (1990). An
alternative astronomical calibration of the lower Pleistocene timescale based on OPD site 677. Transactions
of the Royal Society Edinburgh, Earth Sciences 81,
251–261.
Shackleton, N.J., Crowhurst, S., Hagalberg, T. et al.
(1995). A new late Neogene time scale: application to
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
203
LEG 138 sites. Proceedings of the Ocean Drilling Program, Scientific Results 138, 73–90.
Singer, B., Ackert, R.P., Kurz, M. et al. (1998). Chronology of Pleistocene glaciations in Patagonia: a 3He,
40
Ar/39Ar & K-Ar study of lavas and moraines at Lago
Buenos Aires, 46 S, Argentina. Geological Society of
America 1998 Annual Meeting, Symposium 24,
Abstracts 30, 299.
Singer, B, Ackert, R.P. and Guillou, H. (2004a).40Ar/39Ar
and K/Ar chronology of Pleistocene glaciations in
Patagonia. Geological Society America Bulletin 116,
434–450.
Singer, B., Brown, L., Guillou, H. et al. (1999). 40Ar/39Ar
ages and paleomagnetic data from Cerro del Fraile,
Argentina: further constraints on timing of reversals
during the Matuyama Chron. IUGG Meeting, Abstracts
Volume.
Singer, B., Brown, L.L., Rabassa, J. and Guillou, H.
(2004b). 40Ar/39Ar ages of Late Pliocene and Early
Pleistocene Geomagnetic and Glacial Events in Southern Argentina. AGU Geophysical Monograph Timescales of the Internal Geomagnetic Field, dedicated to
N.D.Opdyke, 176–190.
Singer, B. and Pringle, M.S. (1996). Age and duration of
the Matuyama-Brunhes geomagnetic polarity reversal
from 40Ar/39Ar incremental heating analyses of lavas.
Earth & Planetary Sciences Letters 139, 47–61.
Stiff, B. and Hansel, A. (2004). Quaternary glaciations in
Illinois. In: Ehlers, J. and Gibbard, P. (eds), Quaternary
Glaciations –Extent and Chronology, Part II: North
America. Elsevier, Amsterdam, Developments in Quaternary Science 2, 71–82.
Strelin, J. (1995). New evidence on the relationships
between the oldest extra-andean glaciations in the Rı́o
Santa Cruz area. Quaternary of South America &
Antarctic Peninsula 9. A.A. Balkema Publishers,
Rotterdam, 105–116.
Strelin, J. and Denton, G. (2005). Las morenas de Puerto
Bandera. XVI Congreso Geológico Argentino & IV
Congreso de Exploración de Hidrocarburos, Actas 4,
129–134. La Plata.
Strelin, J. and Malagnino, E.C. (2000). late-glacial history
of Lago Argentino, Argentina, and age of the Puerto
Bandera moraines. Quaternary Research 54, 339–347.
Strelin, J., Re, G., Keller, R. and Malagnino, E. (1999).
New evidence concerning the Plio-Pleistocene landscape evolution of southern Santa Cruz region. Journal
of South American Earth Sciences 12, 333–341.
Sugden, D., Bentley, M., Fogwill, C. et al. (2005). lateglacial glacier events in Southernmost South America:
a blend of ‘‘northern’’ and ‘‘southern’’ hemispheric climatic signals? Geografiska Annaler 87 A, 273–288.
Sugden D., Hulton, N. and Purves, R. (2002). Modelling
the inception of the Patagonian icesheet. Quaternary
International 95–96, 55–64.
Sylwan, C. (1989). Paleomagnetism, Paleoclimate and
Chronology of Late Cenozoic Deposits in Southern
Argentina. Meddelanden Stockholms Universitets Geologiska Institute 277, 1–110.
Thomson, S.N. (2002). Late Cenozoic geomorphic and
tectonic evolution of the Patagonian Andes between
latitudes 42 S and 46 S: An appraisal based on
Els AMS
LPCT
00008
204
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
AU24
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
22-1-2008
14:06
Page:204
Trim:210297 mm
Floats: Top/Bottom
TS: Integra, India
Jorge Rabassa
fission-track results from the transpressional intra-arc
Liquiñe-Ofqui fault zone. Geological Society America
Bulletin 114, 1159–1173.
Tonni, E.P. and Cione, A.L. (1995). Los mamı́feros como
indicadores de cambios climáticos en el Cuaternario de
la Región Pampeana de la Argentina. In: Argollo, J. and
Mourguiart, P. (eds), Cambios Cuaternarios en
América del Sur, ORSTOM, Publicaciones. La Paz,
Bolivia, 319–326.
Tonni, E.P., Cione, A.L. and Figini, A.J. (1999a). Predominance of arid climates indicated by mammals in
the Pampas of Argentina during the late Pleistocene
and Holocene. Palaeogeography, Palaeoclimatology,
Palaeoecology 147, 257–281.
Tonni, E.P., Nabel, P., Cione, A.L. et al. (1999b). The
Ensenada and Buenos Aires formations (Pleistocene) in
a quarry near La Plata, Argentina. Journal of South
American Earth Sciences 12, 273–291.
Ton-That, T. (1997). 40Ar/ 39Ar dating of basaltic lava
flows and the geology of the Lago Buenos Aires region,
Santa Cruz province, Argentina. Unpublished Diploma
Thesis, Université de Genève, Switzerland, 51 pp.
Ton-That, T., Singer, B., Mörner, N.A. and Rabassa, J.
(1999). Datación por el método 40Ar/39Ar de lavas
basálticas y geologı́a del Cenozoico Superior en la
región del Lago Buenos Aires, provincia de Santa
Cruz, Argentina. Asociación Geológica Argentina,
Revista 54, 333–352. Buenos Aires.
Tyson, P.D. and Partridge, T.C. (2000). Evolution of
Cenozoic climates. In: Partridge, T.C. and Maud, R.
(eds), The Cenozoic of Southern Africa. Oxford
University Press, 371–386.
van der Meer, J., Rabassa, J. and Evenson, E. (1992).
Micromorphological aspects of glaciolacustrine sediments in northern Patagonia, Argentina. Journal of
Quaternary Science 7, 31–44.
Verzi, D.H., Tonni, E.P., Scaglia, O.A. and San Cristóbal, J. (2002). The fossil record of the desert-adapted
South American rodent Tympanoctomys (Rodentia,
Octodontidae). Paleoenvironmental and biogeographic significance. Palaeogeography, Palaeoclimatology,
Palaeoecology 179, 149–158.
Volkheimer, W. (1963). El Cuartario pedemontano en el
noroeste de Chubut (zona Cushamen). II Jornadas Geológicas Argentinas, Actas 2, 439–457. Buenos Aires.
Walther, A.M., Rabassa, J., Coronato, A. et al. (2007).
Paleomagnetic studies on glacial sediments in northern
Isla Grande de Tierra del Fuego, Argentina. GEOSUR
Meeting, Abstracts, Santiago de Chile, November 2007.
Warren, C.R. (1993). Rapid recent fluctuations of the
calving San Rafael Glacier, Chilean Patagonia: Climatic
or nonclimatic? Geografiska Annaler 75A, 111–125.
Warren, C.R. (1994). Freshwater calving and anomalous
glacier oscillations: recent behaviour of Moreno
and Ameghino glaciers, Patagonia. The Holocene 4,
422–429.
Warren, C.R, Glasser, N.F., Harrison, S. et al. (1995a).
Characteristics of tide-water calving at Glacier San
Rafael, Chile. Journal of Glaciology 42, 279–291.
Warren, C.R., Sugden, D.E. and Clapperton, C.M.
(1995b). Asynchronous response of Patagonian
glaciers to historic climate change. Quaternary of
Wehrli, L. (1899). Rapport preliminaire sur mon expédition géologique dans la Cordillère Argentine-Chilienne
du 40 et 41 latitude sud (région de Nahuel Huapi),
Argentina. Revista del Museo de La Plata 9, 223–252.
La Plata.
Wenzens, G. (1999a). Evidences of Pliocene and early
Quaternary glaciations east of Lago Viedma (Patagonia, Argentina). Zentralblatt Geologie und Paläontologie 1, 1027–1049.
Wenzens, G. (1999b). Fluctuations of outlet and valley
glaciers in the Southern Andes (Argentina) during the
past 13,000 years. Quaternary Research 51, 238–247.
Wenzens, G. (2000). Pliocene Piedmont Glaciation in the
Rı́o Shehuen Valley, Southwest Patagonia, Argentina.
Arctic, Antarctic & Alpine Research 32, 1, 46–54.
Wenzens, G. (2002). The influence of tectonically
derived relief and climate on the extent of the last
Glaciation east of the Patagonian Ice Fields (Argentina,
Chile). Tectonophysics 345, 329–344.
Wenzens, G. (2004). Comment on ‘‘modelling the inception of the Patagonian ice sheet’’. Quaternary International 112, 105–109.
Wenzens, G. (2006a). Terminal moraines, outwash plains
and lake terraces in the vicinity of Lago Cardiel (49 S,
Patagonia, Argentina): evidence for Miocene Andean
foreland glaciation. Arctic, Antarctic and Alpine
Research 38, 276–291.
Wenzens, G. (2006b). Comment on: Kaplan, M.R.,
Douglass, D., Singer, B.S., Ackert, R.P. and Caffee,
M.W., 2005, Cosmogenic nuclide chronology of
pre-glacial maximum moraines at Lago Buenos Aires,
46 S, Argentina. Quaternary Research 66, 2, 364–366.
Wenzens, G., Wenzens, E. and Schellmann, G. (1996).
Number and types of the piedmont glaciations east of
the Central Southern Patagonian Icefield. Zentralblatt
Geologie und Paläontologie 1, 779–790.
Willis, B. (1914). Physiography of the Cordillera de los
Andes between latitudes 39 and 44 South. 12th International Geological Congress, Canada, ComptesRendu, 733–756.
Zavala, C.A. and Quattrocchio, M. (2001). Estratigrafı́a y
evolución geológica del Rı́o Sauce Grande (Cuaternario), provincia de Buenos Aires. Asociación Geológica Argentina, Revista 56, 25–37.
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm
Els AMS
LPCT
00008_Auq
22-1-2008
14:07
Page:1
Trim:210297 mm
Floats: Top/Bottom
01
TS: Integra, India
AUTHOR QUERY
02
03
Chapter 8
04
05
06
07
08
AU:1
‘‘Rabassa, 2006’’ has been changed to ‘‘Rabassa, 2007’’ in order to match with the reference list. Is this OK?
(Here and elsewhere).
AU:2
‘‘Coronato et al., this volume’’ has been changed to ‘‘Chapter 3’’. Please confirm whether this change is OK.
AU:3
‘‘Wherli (1899)’’ has been changed to ‘‘Wehrli (1899)’’ in order to match with the reference list. Is this OK?
AU:4
‘‘Groeber (1956)’’ has been changed to‘‘Groeber (1952)’’ in order to match with the reference list. Is this OK?
AU:5
‘‘Ton That et al., 1999’’ has been changed to ‘‘Ton-That et al., 1999’’ in order to match with the reference
list. Is this OK?
AU:6
‘‘Rabassa, 1996’’ is not listed in the reference. Please check.
AU:7
‘‘Pankhe et al., 2003’’ has been changed to ‘‘Panhke et al., 2003’’ in order to match with the reference list. Is
this OK?
AU:8
‘‘Pahnke et al., 2003’’ has been changed to ‘‘Panhke et al., 2003’’ in order to match with the reference list. Is
this OK?
AU:9
‘‘McCulloch et al. (2005a)’’ has been changed to ‘‘McCulloch et al. (2005)’’ in order to match with the
reference list. Is this OK?
AU:10
‘14.714C ka yr BP’ has been changed to ’14.7.14C kyr BP’. Is this OK?
AU:11
Please clarify whether this should be ‘‘1’’ or ‘‘I’’ in ‘‘Llanquihue 1’’, ‘‘Heinrich 1’’ in all occurences.
AU:12
Please clarify ‘‘Rabassa, et al. 1990a or 1990b or 1990c’’.
AU:13
‘‘Clapperton and Sugden (1988)’’ has been changed to ‘‘Clapperton and Sugden (1989)’’ in order to match
with the reference list. Is this OK?
AU:14
‘‘Clapperton and Sugden (1984)’’ has been changed to ‘‘Clapperton and Sugden (1986)’’ in order to match
with the reference list. Is this OK?
AU:15
‘Map of South America during the LGM. Partly modified from Clapperton, 2003’ has been changed to ‘Map
of South America during the LGM. Partly modified from Clapperton, 1993’. Is this OK?
AU:16
‘‘this volume’’ has been changed to ‘‘Chapter 12’’. Please confirm whether this change is OK.
AU:17
Please clarify ‘‘Heusser, 1989a or 1989b.’’
AU:18
‘‘Tonni and Cione, 1995; Tonni and Carlini, this volume’’ has been changed to ‘‘Chapter 13’’. Please confirm
whether this change is OK.
AU:19
‘‘Tonni and Cione, 1999’’ is not listed in the reference. Please check.
AU:20
‘‘Schellman, 1998’’ has been changed to ‘‘Schellman, 1998’’ in order to match with the reference list. Is this
ok? (here & elsewhere)
AU:21
Please provide volume number and page range.
AU:22
Please provide publishing details for ‘Pascual, R., Ortiz Jaureguizar, E. and Prado, J. (1996)’.
AU:23
Please provide publishing place for ‘Rabassa, Rublis and Brandani, 1980’.
AU:24
Please provide teh publishing place for ‘Tyson, P. D. and Partridge, T. C. (2000)’.
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Font: Times
Font Size:10/13pt
Margins:Top:17mm
Gutter:15mm
T.Area: 170mm

8 Late Cenozoic Glaciations in Patagonia and Tierra del Fuego

Transcription

Similar documents

How to Tie a Woggle

lnstallation - ConservationMart.com

Turkey - EOPOWER

here - First Descents

Key - Scioly.org

RÉSoNANSS: a regional contribution to

Real Time Control of Hand Prosthesis Using Surface EMG

Kerntech Diagnose-System Loose Part Monitoring System

CoUNTerMEASURES CoUNTerMEASURES

PrimeFilm 1800 AFL Low-Cost 35mm Slide/Film Scanning Through