OLIGOCENE - LOWER MIOCENE EVENTS IN ROMANIA

ACTA PALAEONTOLOGICA ROMANIAE V. 6 (2008), P. 203-215.
OLIGOCENE - LOWER MIOCENE EVENTS IN ROMANIA
Mihaela MELINTE-DOBRINESCU1 & Titus BRUSTUR1
Abstract. This paper is focused on the biotical and lithological markers, which are present in the Eastern
Carpathians and in NW Transylvania, and allows correlation of the Oligocene-Lower Miocene deposits of
these two regions. In the both above-mentioned areas, the debut of the Oligocene is characterized by the
instauration of an anoxic/hypoxic regime, related to the paleogeographic changes of those times (i.e., the
first isolation of the Paratethys from Mediterranean). This event is marked by the appearance of endemic
(Paratethyan) nannofloras in the Carpathian and Transylvanian areas, accompanied by endemic mollusc
faunas, and slightly preceded by blooms of the low-salinity nannofossil Braarudosphaera bigelowii. Within
the Early Oligocene interval, coccolithic laminitic limestones (Tylawa type) were accumulated within the
NP23 Calcareous Nannofloral Zone. The Rupelian laminitic limestone contains bloom of endemic
Paratethyan nannofossils. During the Late Oligocene interval, coccolithic laminitic limestones (Jasło type)
were identified both in the Eastern Carpathians and NW Transylvania, in the NP24 Calcareous Nannofossil
Zone, and yielded blooms of cosmopolitan nannofloral taxa. The youngest level of coccolithic laminitic
limestones (Zagórz type) was identified in uppermost Oligocene deposits of the Eastern Carpathians (within
the NP25 Calcareous Nannofloral zone, Late Chattian in age), while in the Transylvanian area this marker
was not found so far. The Oligocene/Miocene boundary (approximated by the first occurrence of the
nannofossil Sphenolithus capricornutus) is pointed out both in the Eastern Carpathian and NW
Transylvanian areas by a tuff level (placed within the NN1 Calcareous Nannofossil Zone). Around the
Aquitanian/Burdigalian boundary (within the NN2 Calcareous Nannoplankton Zone), another tuff level was
deposited in the southern and central regions of the Eastern Carpathians.
Key words. Oligocene-Lower Miocene; lithology; bio-events; Eastern Carpathians; NW Transylvania.
INTRODUCTION
The Oligocene is associated with a climatic
deterioration (Aubry, 1992), expressed by an
overall significant temperature decrease
(Zachos et al., 2001), and by the instauration
of ice caps in the Antarctic region. These
changes are accompanied by a major sealevel fall, according to Haq et al., 1988 (Fig.1),
concomitantly with a global ocean-land
reorganization (Scotese, 2002).
Additionally, the very active tectonic regime
of the Oligocene interval led to important
paleogeographic modifications: the Tethys
Ocean was divided, in the European regions,
in two main branches (i.e., the Mediterranean
and the Paratethys - Báldi, 1980; Rusu, 1988;
Săndulescu & Micu, 1989; Rögl, 1998).
Becoming isolated from the Mediterranean, the
Paratethys domain displayed a distinct
paleobiogeography, hydrological regime, and
sedimentation
dynamic.
Therefore,
the
stratigraphers use regional stages for the two
main Paratethys branches, including for the
Central Paratethys (Cicha et al., 1998, Fig. 2)
where the present Romanian territory was
located (Mészáros, 1989; Rusu, 1989, Rögl,
1999, among many others).
Around the Eocene/Oligocene boundary
interval, the termohaline water stratification
and the primarily estuarine water circulation
pattern, eventually resulting in recurrent
episodes of stagnation, characterized the
Paratethys
domain,
leading
to
the
accumulation of hypoxic to anoxic sediments.
Fig. 1 Late Eocene-Early Miocene global climatic and sea-level fluctuations (climatic events and
average global temperature after Zachos et al., 2001; sea-level after Haq et al., 1988).
1
National Institute of Marine Geology and Geo-ecology, Street Dimitrie Onciul, No. 23-25, RO-024053, Bucharest, Romania,
e-mail: [email protected], [email protected]
M. MELINTE-DOBRINESCU & T. BRUSTUR
Fig. 2 Correlation of global stages with the central Paratethys stages, and with the foraminiferal and
calcareous nannoplankton biozones (modified after Berggren et al., 1995 and Cicha et al., 1998). PPaleogene Foraminiferal Zones; M-Miocene Foraminiferal Zones; NP-Paleogene Calcareous
Nannoplankon Zones; NN-Neogene Calcareous Nannoplankton Zones.
Such type of deposition prevailed during
the whole Oligocene and Lower Miocene
times, and is referred as “the menilite and
dysodile facies” in the Central Paratethys,
including Romania (for a synthesis see
Popescu et al., 1995 and Rusu et al., 1996).
Intervals of high productivity water surface
allow the accumulation of several levels of
coccolithic laminitic limestones in the whole
Central Paratethys (fide Uhlig, 1883; Nowak,
1965; Haczewski, 1981, 1989; Nagymarosy &
Voronina, 1992; Krhovský et al., 1992;
Švábenická et al., 2007), including Romania
(Grasu et al., 1982; Alexandrescu & Brustur,
1985; Ionesi, 1986; Brustur & Alexandrescu,
1989; Ştefănescu et al., 1989; Melinte, 2005).
The
Oligocene
coccolithic
laminitic
limestones represent excellent lithological
markers, very useful for correlations in the
whole Carpathian area. During the Oligocene
- Lower Miocene, tuff levels are also known to
occur in different areas from Romania; hence,
they could be regarded as lithological markers,
useful for regional correlations.
The aim of this paper is to reveal the
lithological and paleobiological markers, which
could be valuable for Oligocene-Lower
Miocene stratigraphical correlation. Two
Romanian regions were mainly investigated
(i.e., the NW Transylvania, namely the Preluca
204
sedimentation area, and the central-southern
part of the Eastern Carpathians) (Fig. 3).
GEOLOGICAL SETTING
NW Transylvania
In the NW Transylvania, three distinct
Paleogene sedimentation areas (Gilău, Meseş
and Preluca) were distinguished (Rusu, 1970).
In particular, the Preluca area displays a
continuous marine sedimentation within the
Oligocene-Early Miocene interval. Hence, the
Early Oligocene is marked by the deposition of
the Cuciulat Formation, mainly composed of
grey and brown marlstones and claystones,
followed by the bituminous marls of the Bizuşa
Formation and the bituminous shales of the
Ileanda Formation (Fig. 4).
The
Late
Oligocene
interval
is
characterized by the sedimentation of the
Buzaş Formation, mainly made by an
alternance of sandstones and marls, and by
the younger lutite, hemipelagic Vima
Formation. Towards NE, the Vima Formation
progressively replaced the Buzaş Formation.
The
Oligocene/Miocene
boundary
(the
boundary between the NP25/NN1 Calcareous
Nannoplankton Zone of Martini, 1971) was
previously identified, based on calcareous
nannofossil assemblages, in the Vima
formation (Mészáros et al., 1979; Mészáros &
Ianoliu, 1989; Rusu et al., 1996).
OLIGOCENE-LOWER MIOCENE EVENTS IN ROMANIA
Fig. 3 Location of the Oligocene-Lower Miocene studied sections in the NW Transylvania and in
the central and southern part of the Eastern Carpathians.
Eastern Carpathians
The Oligocene-Lower Miocene sediments
crop out on large areas in the Eastern
Carpathians, belonging to (1) the sedimentary
cover of the Moldavid Nappes (Outer Flysch
Zone), (2) the post-tectonic cover of the Outer
Dacid Nappes, and (3) the Pienid tectonic units
(Săndulescu, 1984). Within the Moldavids, in
the outer (eastern) part of the central and
southern Eastern Carpathians, the OligoceneLower Miocene formations are involved in the
Tarcău, Marginal Fold and Subcarpathian
nappes, where they display two main
lithofacies, namely the Bituminous Kliwa
Facies in the external part and the FusaruPucioasa Facies (similar to the Polish
Carpathian Krosno facies), in the inner part Săndulescu & Micu, 1989.
During the Paleogene, varying rates of
subsidence were recorded in the Moldavids
(Ştefănescu & Melinte, 1996). The subsidence
was faster in the Eocene, Late Oligocene and
Early Miocene, when mostly terrigenous rocks
(flysch and molasses deposits) accumulated,
and lower within the Late Eocene-Early
Oligocene
interval,
when
a
pelagic
sedimentation prevailed.
The Early Oligocene interval (= the
Rupelian stage) is characterized in both
lithofacies by the deposition of the Lower
Dysodile Shale Formation, composed of
bituminous shales with frequent sulphur and
disarticulated fish remains (Fig. 5).
In the eastern (outermost) Kliwa Facies, the
base of the Oligocene is characterized by the
sedimentation of the Lower Menilite Formation,
consisting of cherts and bituminous marls,
followed by the Lower Dysodile Shale
Formation, composed of bituminous shales.
During Late Oligocene times (= the Chattian
stage), in the inner Fusaru-Pucioasa
lithofacies, turbiditic sequences made by
calcareous sandstones interbedded with
bituminous marls, as well as green and gray
pelites, occur. Within the outer lithofacies, the
same interval consists of the Kliwa Sandstone
Formation,
including
white
massive,
orthoquartzitic sandstones interlayered with
thin bituminous shales.
Around the Oligocene/Miocene boundary
interval, shaly turbidites were deposited,
namely the Vinetişu Formation in the inner
facies, and the Podu Morii Formation in the
outer facies (the later unit shows in addition
prominent
convolute
sandstones).
The
Oligocene/Miocene boundary was identified,
based
on
calcareous
nannoplankton
investigations, towards the base of the two
above-mentioned units (Melinte, 1988; Ionesi
& Mészáros, 1989; Micu et al., 1989; Ionesi et
al., 1998; Mărunţeanu, 1999; Melinte et al.,
1999; Melinte, 2005), within the NN1
Nannofossil Zone of Martini (1971) – Fig. 5.
205
M. MELINTE-DOBRINESCU & T. BRUSTUR
Fig. 4 Lithology and main biotical events recorded in the Preluca area, NW Transylvania (modified
after Rusu, Popescu & Melinte, 1996).
206
OLIGOCENE-LOWER MIOCENE EVENTS IN ROMANIA
Fig. 5 Lithology and main biotical events recorded in the central and southern part of the Eastern
Carpathians (modified after Melinte, 2005).
LITHOLOGICAL AND BIOTICAL MARKERS
Early Oligocene
The restricted Early Oligocene circulation of
the Paratethys realm, which led to the
instauration of a hypoxic to anoxic regime, is
mirrored in the sedimentation of both the NW
Transylvania and Eastern Carpathian regions.
There, the bituminous marls and shales of the
Bizuşa and Ileanda units (in NW Transylvania),
as well as the bituminous cherts, marls and
shales of the Menilite and Lower Dysodile
formations (in the Eastern Carpathians) were
deposited within the Rupelian (=Early
Kiscellian interval).
The initiation of the anoxic sedimentation is
reflected in the calcareous nannoplankton
fluctuation.
The
cosmopolitan
Eocene
nannofossils are sharply replaced by endemic
taxa. The five Early Rupelian nannofloral
extinctions of Discoaster saipanens Bramlette
& Riedel, D. barbadienis Tan, Clausicoccus
subdistichus (Roth & Hay) Prins, Discoaster
tanii (Bramlette & Riedel) Bukry and
Helicosphaera reticulata Bramlette & Wilcoxon
are followed by another seven extinctions in
the upper Rupelian (NP23 Nannofossil Zone),
when
Isthmolithus
recurvus
Deflandre,
Reticulofenestra hillae Bukry & Percival, R.
umbilica
(Levin)
Martin
&
Ritzowski,
Orthozygus aureus (Stradner) Brameltte &
Wilcoxon, Lanternitus minutus Stradner,
Chiasmolithus oamaruensis (Deflandre) Hay,
Mohler & Wade and Transversopontis fibula
Gheţa disappeared (Figs. 4, 5). Between these
two groups of extinctions, at the end of the
early Rupelian (in NP23a Nannofossil Subzone
of Melinte, 1995), the endemic nannofossils
Reticulofenestra lockeri Müller, R. ornata
Müller, Transversopontis fibula Gheţa and T.
latus Müller appeared (Pl. 1). The succession
of these nannofloral events were recorded in
all the sections investigated from the NW
Transylvania, as well as from the central and
southern part of the Eastern Carpathians.
Moreover,
these
bioevents
could
be
recognized everywhere in Romania (i.e., in the
Getic Depression, according to Roban &
Melinte, 2006), where continuous Early
Oligocene rock-sequences crop out.
In NW Transylvania, a distinct bio-horizon
with the endemic Paratethyan macrofaunal
taxa “Cardium” lipoldi and Janschinella
garetzkii is present, towards the base of the
Bizuşa Formation (Rusu, 1988; Rusu et al.,
1996), within the lower part of the NP23
Nannofossil Zone. The Janschinella garetzkii
bio-horizon is present also in the Eastern
Carpathians, towards the base of the Lower
Dysodile Formation, in the same stratigraphic
position (i.e., Lower Rupelian), according to
Rusu (1999). Remarkably, synchronously with
the occurrence of the Janschinella garetzkii
macrofaunal level, monospecific calcareous
nannoplankton
assemblages,
with
Braarudosphaera bigelowii (Gran & Braarud)
207
M. MELINTE-DOBRINESCU & T. BRUSTUR
Deflandre, was identified in the investigated NW
Transylvanian region.
In several sections from the Preluca area of
NW Transylvania (the better exposure being
located in the Poienii Valley, the Fântânele
Village – Fig. 4) several cm coccolithic laminitic
limestones (Coccolithic limestone 1) occur,
within the lower part of the bituminous shales
of the Ileanda Formation (around the boundary
of the NP23a/b Calcareous Nannofossil
Subzones of Melinte, 1995). In the whole
Eastern Carpathian bend, coccolithic laminitic
limestones are present towards the base of the
Lower Dysodile Formation, yielding also a
Rupelian age (Fig. 5). Both in the NW
Transylvania and in the Eastern Carpathians,
the laminas of the Rupelian limestone are
made by blooms of the endemic Paratethyan
nannofossils, such as Reticulofenestra ornata,
R. lockeri and Transversopontis fibula (Pl. 1).
Below the Early/Late Oligocene boundary
(= the Rupelian/Chattian boundary, placed in
the NP24 Calcareous Nannofossil Zone according to Berggren et al., 1995) the
endemic Paratethyan nannofossils vanished,
and new cosmopolitan taxa (Young, 1998),
such as Sphenolithus ciperoensis Bramllete &
Wilcoxon and Chiasmolithus altus Bukry and
Percival, appeared (Figs. 4 and 5).
Synchronously,
the
pelitic
anoxic
sedimentation is replaced by sandy-shaly
turbidites in the Eastern Carpathians (with
more frequent bituminous rocks in the outer
facies), and by sandstones and clays in the
NW Transylvanian area.
Late Oligocene
The
Late
Oligocene
(Chattian=Late
Kiscellian and Early Egerian) is an interval
characterized by cosmopolitan nannofloral
assemblages
in
both
the
Preluca
sedimentation area (NW Transylvania) and in
the Eastern Carpathians. In fact, the
nannoplankton zones of Martini (1971),
completed with the Subzones of Melinte (1995)
could be recognized in all the Upper Oligocene
succesions from Romania (Figs. 4 and 5).
In the both inner and outer Oligocene facies
of the Eastern Carpathians, a coccolithic
laminitic limestone (Coccolithic limestone 2)
was deposited.
Several
cm to dm
intercalations of this limestone could be
observed from the northern part of the Eastern
Carpathians until the bend area, in the
Pucioasa-Fusaru Formation and in its outer
equivalent, the Lower Kliwa Sandstone
Formation (Fig. 5). The Lower Chattian
laminitic limestone (placed in the NP24
Calcareous nannofossil Zone) contains, in its
laminas, bloom of cosmopolitan nannoplankton
208
species, such as Dictyococcites bisectus (Hay,
Mohler & Wade) Bukry & Percival,
Zygrhablithus bijugatus (Deflandre) Deflandre,
Cyclicargolithus floridanus (Roth & Hay) Bukry
and Sphenolithus moriformis (Brönnimann &
Stradner) Bramlette & Wilcoxon (Pl.1).
The Lower Chattian laminitic limestone
(Coccolithic limestone 2) is also present in the
NW Transylvanian area (Rusu et al., 1996),
placed in the Buzaş Formation (one of the best
section where it is exposed is the Runcului
Valley, Fig. 4). The nannofloral assemblages
observed in the white laminas of this limestone
are similar with those from the Eastern
Carpathians and belong also to the NP 24
Calcareous Nannoplankton Zone.
Besides Lower Chattian coccolithic laminitic
limestone identified in thr both NW
Transylvanian and in the Eastern Carpathian
regions, another Chattian distinct level of
coccolithic laminitic limestones (Coccolithic
limestone 3) was observed only in the Eastern
Carpathian bend. This is placed din the NP
25a Calcareous Nannoplankton Subzone,
between the first occurrence of Pontosphaera
enormis (Locker) Perch-Nielsen and the first
occurrence of Triquetrorhabdulus carinatus
Martini, being Late Chattian in age (Fig. 5).
Below the Coccolithic limestone 3, towards
the Oligocene top (in the latest Chattian) a
high
abundance
of
the
calcareous
nannoplankton Sphenolithus and Discoaster
genera was observed in the nannofloral
assemblages. The two above-mentioned
genera jointly amount to almost 50% of the
total recorded nannofloras. This event was
recognized only in the Eastern Carpathians,
within the upper part of the Pucioasa-Fusaru,
and respectively in the Lower Kliwa Sandstone
formations.
Early Miocene
The Oligocene/Miocene boundary was
recognized both in the NW Transylvania and
Eastern Carpathians based on calcareous
nannofossil assemblages. This boundary is
placed within the NN1 Calcareous Nannofossil
Zone (Berggren et al., 1995), and it is
approximated by the first occurrence (FO) of
Sphenolithus
capricornutus
Bukry
and
Percival. Based on this bio-event we placed
the Oligocene/Miocene boundary in the
Eastern Carpathians towards the lower part of
the Vineţişu Formation (in the inner facies),
and within the lower part of the Podu Morii
Formation (within the outer facies) (Fig. 5).
Just above the FO of Sphenolithus
capricornutus, a thin cm level of green tuff,
described by Ştefănescu et al. (1989) as the
Vineţişu Tuff, was observed in the both
OLIGOCENE-LOWER MIOCENE EVENTS IN ROMANIA
Oligocene facies of the Eastern Carpathians.
This tuff is synchronous with the tuff observed
in the NW Transylvania, the Valea Cocii Tuff,
well preserved in the Cocii Valley (Măgoaja
Village). A younger tuff level (a 50 cm white
tuff, described as the Mlăcile Tuff by
Ştefănescu et al., 1989, and as the Vălenii de
Munte Tuff by Alexandrescu et al., 1994) is
present in the Eastern Carpathians (very well
exposed in the southern part, between the
Buzău and Teleajen valleys) and also in
northern sectors (i.e., the Trotuş Valley at
Târgu-Ocna, Alexandrescu & Brustur, 1996).
This
tuff
is
placed
around
the
Aquitanian/Burdigalian
boundary,
shortly
above
the
FO
of
Reticulofenestra
pseudoumbilicus Gartner (< than 7 µm), within
the NN2 Calcareous Nannofossil Zone.
In the Trotuş Valley basin, tuff and
bentonites were identified in the Upper
Dysodile Formation of the Kliwa Sandstone
Facies (Alexandrescu & Brustur, 1996).
Several thin cm up to dm tuff levels were
identified by the above-mentioned authors,
who described them as ‘the Livadea
bentonites”. Notably, towards the top of the
Upper Dysodile Formation, within the Early
Burdigalian. a thicker tuff (3-4m) was
observed, being described as “the Falcău Tuff”
(Alexandrescu & Brustur, 1996).
DISCUSSION
Several levels of coccolithic laminitic
limestones were identified in the NW
Carpathians and Eastern Carpathian regions.
We described herein these limestones as
Coccolithic limestones, and they could be
correlated (as age and lithology) with those
described in other Carpathian areas (in
particular in the Polish Carpathians –
Haczewski, 1981; 1989) as follows: Coccolithic
limestone 1 – the Tylawa Limestone (Rupelian
in age), Coccolithic limestone 2 – the Jasło
Limestone (Early Chattian in age), and
Coccolithic limestone 3 - the Zagórz Limestone
(Late Chattian in age).
Even if these coccolithic limestones were
sedimented during different paleogeographical
settings, their deposition is probably due to
similar paleonevironmental conditions, related
to a high nutrient input and absence of other
planktonic competitors (i.e., foraminifers) than
the calcareous nannoplankton. The Coccolithic
limestone 1 (= the Tylawa limestone) was
deposited during the first isolation of the
Paratethys from the Mediterranean (the NP 23
Calcareous Nannoplankton Zone), fact argued
by the presence of endemic nannofloras.
Moreover, the occurrence of nannofloral
monospecific
assemblages
with
Braarudosphaera bigelowii (which blooms are
related to low salinity surface waters –
Lamolda et al., 2005 and cooler waters –
Siesser et al., 1992) indicates an important
shift of salinity, and probably a temperature
decrease. Notably, Rupelian blooms of
Braarudosphaera bigelowii were also recorded
in other Carpathian areas (Krhovský et al.,
1992; Nagymarosy & Voronina, 1992).
The occurrence of the Coccolithic limestone
2 (= the Jasło Limestone) in the whole
Paratethys area, including the present
Romanian territory, is related to the restoration
of the communication between the Paratethys
and the Mediterranean, within Late Oligocene
(= Chattian) times, in the NP24 Calcareous
Nannoplankton Zone respectively. It is to
assumed
that
similar
paleogeographic
conditions lasted in the upper part of the
Chattian, when the youngest Oligocene
laminitic limestone, Coccolithic limestone 3 (=
the Zagórz Limestone), was sedimented, in the
NP25 Calcareous Nannoplankton Zone.
Remarkably,
both Chattian laminitic
limestones (i.e., Jasło and Zagórz) yielded
blooms of cosmopolitan nannofossils. Such
blooms,
of
Dictyococcites
bisectus,
Zygrhablithus
bijugatus,
Cyclicargolithus
floridanus and Sphenolithus moriformis were
recorded in the whole Carpathian area in the
above-mentioned nannoplankton zones, even
in the absence of the laminitic limestones
(Bubík, M., 1987; Švábenická et al., 2007).
Consequently, the nannoplankton blooms are
important Upper Oligocene biostratigraphical
horizons, and could be used for Paratethys
correlation.
Between the depositional intervals of the
Coccolithic limestone 2 and 3 (Jasło and
Zagórz respectively), a bloom of the
sphenoliths and discoasters, nannofossils
related to an open marine setting and warm
surface temperature (Aubry, 1992; Fornaciari
& Rio, 1996), was identified. This nannofloral
event could regionally expressed the global
Late Oligocene Warming Event (Zachos et al.,
2001), synchronous with the sea-level rise
(Fig. 6).
Taking into account the Oligocene
nannofloral fluctuation pattern, we may
assume that the Early Oligocene was
characterized in the both studied Romanian
areas by a significant cooling, followed by an
increase of the temperature in Late Oligocene
(Chattian) times. A similar paleoclimatic
scenario was hypothesized, based on
palynological evidence, by Olaru (1989). The
above-mentioned author reported an important
temperature shift at the base of the Oligocene,
based on the presence of Arctic Tertiary
209
M. MELINTE-DOBRINESCU & T. BRUSTUR
Fig. 6 Main Oligocene-Lower Miocene lithological and biotical (calcareous nannofossil) markers of
the NW Transylvanian and Eastern Carpathian regions.
angiosperms, followed by a slight climatic
warming in the depositional interval of the
Fusaru, and respectively Kliwa Sandstone of
the Eastern Carpathians.
Tuff and bentonites are well-known in the
Oligocene-Lower Miocene sediments of the
Eastern Carpathians, from the northern
boundary of Romania up to Carpathian bend
area (Mutihac & Ionesi, 1973; Catană et al.,
1982; Mârza & Voiculescu, 1991). In particular,
in the Moldavid tectonic units, thin cm tuff and
bentonites occur in the Early Oligocene
(Rupelian) Lower Menilite and Lower Dysodile
formations, as well as in the Early Miocene
(Burdigalian) Upper Menilite and Upper
Dysodile lithological units (Alexandrescu et al.,
1984, 1991; Ştefănescu et al., 1989), and may
represent, regionally, useful lithological
markers.
Another tuff level is the Vineţişu tuff,
identified in the both Moldavid facies,
210
Pucioasa-Fusaru and Lower Kliwa Sandstone
(Ştefănescu et al., 1989). This green tuff, 2530 cm in thickness, occurs slightly above the
Oligocene/Miocene boundary (above the first
occurrence of the nannofossil Sphenolithus
capricornutus, according to Melinte, 1988,
2005), and it is synchronous with the Valea
Cocci tuff deposited in the NW Transylvania
(Preluca sedimentation area). Another reliable
event is the deposition of the 40-50 cm in
thickness white Mlăcile Tuff, which could be a
good marker to emphasize the Burdigalian
base, at least in the southern and central parts
of the Eastern Carpathians.
SUMMARY
The investigation of the Oligocene-Lower
Miocene sediments of the NW Transylvania
(Preluca sedimentation area) and of the
Eastern Carpathians allows us to recognize
OLIGOCENE-LOWER MIOCENE EVENTS IN ROMANIA
several events, which are, in the stratigraphical
succession, the following (Fig. 6):
- The anoxic/hypoxic deposition, which
marks the debut of the Oligocene;
The presence of monospecific
assemblages with Braarudosphaera bigelowii,
within the Rupelian (Early Kiscellian), around
the base of
the NP23 Calcareous
Nannoplankton Zone;
- The appearance of the endemic
Paratethyan nannofloras, synchronously with
the occurrence of the Paratethys macrofaunal
bio-horizon with “Cardium” lipoldi and
Janschinella garetzkii, also in the NP23
Calcareous Nannoplankton Zone;
- The deposition, in the Late Rupelian
(Early Kiscellian), of the Coccolithic limestone
1 (the Tylawa Limestone), which contains
blooms of endemic nannofossils, within the
upper part of NP23 Calcareous Nannofossil
Zone;
- The extinction of the endemic Paratethys
nannofloras around the top of the NP 23
Calcareous Nannofossil Zone;
- The deposition, in the Early Chattian (Late
Kiscellian), of the Coccolithic limestone 2 (the
Jasło Limestone), which contains blooms of
cosmopolitan nannofossils, within the NP24
Calcareous Nannofossil Zone;
- The occurrence of the Sphenolithus spp.
and Discoaster spp. nannofossil blooms;
- The deposition, in the Late Chattian (the
top of the Kiscellian), of the Coccolithic
limestone 3 (the Zagórz Limestone), which
contains blooms of cosmopolitan nannofossils,
within NP25 Calcareous Nannofossil Zone;
- The FO of the nannofossil Sphenolithus
capricornutus,
which
approximates the
Oligocene/Miocene boundary (Early Egerian);
- The deposition of a tuff (referred as the
Vineţişu Tuff in the Eastern Carpathians and
the Valea Cocii Tuff in the NW Transylvania),
slightly
above
the
Oligocene/Miocene
boundary,
in
the
NN1
Calcareous
Nannoplankton Zone;
- The deposition of the Mlăcile Tuff in the
Eastern Carpathians, around the base of the
Burdigalian (in the Eggenburgian), within the
NN2 Calcareous Nannoplankton Zone.
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PLATE 1
LM, All the microphotographs are N+, except Figs. 12 and 20 which are in NII
Fig. 1. Braarudosphaera bigelowii (Gran & Braarud) Deflandre, Poienii Valley (Fântânele Village),
Bizuşa Formation, NP22 Biozone.
Fig. 2. Reticulofenestra pseudoumbilicus (Gartner), Buzău Valley, Podu Morii Formation, NN2
Biozone.
Fig. 3. Helicosphaera carteri (Wallich) Kamptner, Buzău Valley, Podu Morii Formation, NN2 Biozone.
Fig. 4. Sphenolithus moriformis (Brönnimann & Stradner) Bramlette & Wilcoxon, Vineţişu section,
Pucioasa Formation, NP 24 Biozone.
Fig. 5. Bloom of Reticulofenestra ornata Müller, Bâsca Rozilei (Nehoiaşu), Tylawa Coccolithic
Limestone, NP 23 Biozone.
Fig. 6. Bloom of Dictyococcites bisectus (Hay, Mohler & Wade) Bukry & Percival and Zygrhablithus
bijugatus (Deflandre) Deflandre, Vineţişu section, Jaslo Coccolithic Limestone, NP 24
Biozone.
Fig. 7. Transversopontis fibula Gheta, Târgu-Ocna Section, Lower Dysodilic Fomation, NP23 Biozone.
Fig. 8. Pontosphaera multipora (Kamptner) Roth and Braarudosphaera bigelowii (Gran & Braarud)
Deflandre, Târgu-Ocna Section, Lower Menilite Formation, NP22 Biozone.
Fig. 9. Reticulofenestra ornata Müller, Târgu-Ocna Section, Lower Dysodilic Fomation, NP23 Biozone
Fig. 10. Reticulofenstra lockeri Müller, Târgu-Ocna Section, Lower Dysodilic Fomation, NP23 Biozone.
Fig.11. Pontosphaera enormis (Locker) Perch-Nielsen, Runcului Valley (Poiana Blenchii), Buzaş
Formation, NP25 Biozone.
Fig. 12. Discoaster barbadiensis Tan, Bâsca Rozilei Valley (at Nehoiaşu), Plopu Formation, NP21
Biozone.
Fig. 13. Rhabdosphaera clavigera Murray & Blackman and small reticulofenstrids, Cocii Valley
(Măgoaja Village), Vima Formation, NN1 Biozone.
Fig. 14. Chiasmolithus altus Bukry & Percival, Runcului Valley (Poiana Blenchii), Buzaş Formation, NP
24 Biozone.
Fig. 15 a, b. Sphenolithus ciperoensis Bramlette & Wilcoxon, a- 450, b-00; Buzău Valley, Podu Morii
Formation, NP25 Biozone.
Fig. 16. Sphenolithus capricornutus Bukry & Percival, Vineţişu section, Vineţişu Formation, NN 1
Biozone.
Fig. 17. Sphenolithus conicus Deflandre and Sphenolithus belemnos Bramlette & Wilcoxon, Buzău
Valley, Podu Morii Formation, NN2 Biozone.
Fig. 18. Helicosphaera scissura Miller, Buzău Valley, Podu Morii Formation, NN1 Biozone.
Fig. 19. Discoaster deflandrei Bramlette & Riedel, Vineţişu section, Pucioasa Formation, NP 25
Biozone.
Fig. 20. Reticulofenstra umbilica (Levin) Martin & Ritzkowski, Poienii Valley (Fântânele Village), Bizuşa
Formation, NP23 Biozone, N II
Fig. 21. Reticulofenstra umbilica (Levin) Martin & Ritzkowski, Poienii Valley (Fântânele Village), Bizuşa
Formation, NP23 Biozone, N +.
214
M. MELINTE-DOBRINESCU & T. BRUSTUR
PLATE I
215