Cambrian acritarchs from the Bourinot belt, Cape Breton Island

Transcription

289
Cambrian acritarchs from the Bourinot belt, Cape
Breton Island, Nova Scotia: age and stratigraphic
implications1
Teodoro Palacios, Sören Jensen, Chris E. White, and Sandra M. Barr
Abstract: We present the first description of organic-walled microfossils from Cambrian strata of the Bourinot belt, central
Cape Breton Island. Age-diagnostic acritarchs have been recovered from the Dugald and MacMullin formations and from
probable levels within the upper part of the Eskasoni Formation, which permit detailed correlations with acritarch-based
zones in Newfoundland and Spain. The assemblage of acritarchs from the Dugald Formation confirms earlier assignments to
the early middle Cambrian eteminicus Zone, but it also indicates that the upper part of the formation belongs to the hicksi
Zone of the Drumian Stage. Acritarchs from the MacMullin Formation provide the first biostratigraphic evidence that this
unit extends into the forchhammeri Zone of the Guzhangian Stage. These acritarchs are present in the lower part of the
MacMullin Formation, putting into question earlier identification of hicksi Zone trilobites in this unit and raising the possibility of an unconformity. The data from the Bourinot belt provide additional evidence for the biostratigraphic utility of acritarchs in the Cambrian Acado-Baltic province.
Résumé : Nous présentons la première description de microfossiles à parois organiques des strates cambriennes de la ceinture de Bourinot, du centre de l’île du Cap-Breton. Des acritarches pouvant déterminer l’âge des fossiles ont été cueillis des
formations de Dugald et de MacMullin, et de niveaux probables de la partie supérieure de la Formation d’Eskasoni, ce qui
permet des corrélations détaillées avec des zones basées sur des acritarches à Terre-Neuve et en Espagne. L’assemblage des
acritarches de la Formation de Dugald confirme les assignations antérieures à la zone à eteminicus du Cambrien moyen précoce, mais il indique aussi que la partie supérieure de la formation appartient à la zone à hicksi de l’étage Drumien. Des
acritarches de la Formation de MacMullin fournissent la première évidence biostratigraphique que cette unité s’étend dans la
zone à forchhammeri de l’étage Guzhangien. Ces acritarches sont présents dans la partie inférieure de la Formation de MacMullin, remettant en question une identification antérieure de trilobites de la zone à hicksi dans cette unité et soulevant la
possibilité d’une discordance. Les données de la ceinture de Bourinot fournissent des preuves additionnelles de l’utilité biostratigraphique des acritarches dans la province acado-baltique cambrienne.
[Traduit par la Rédaction]
Introduction
The Bourinot belt is a narrow fault-bounded band of lower
Palaeozoic sedimentary and volcanic rocks that extends for
about 30 km in a southwest–northeast direction in central
Cape Breton Island, Nova Scotia (White et al. 1994; Figs. 1,
2). Bimodal volcanic rocks, shale, and sandstone of the Bourinot Group form the lower part of the succession and are divReceived 3 October 2010. Accepted 28 January 2011. Published
at www.nrcresearchpress.com/cjes on 22 December 2011.
Corresponding Editor: Brendan Murphy.
T. Palacios and S. Jensen. Area de Paleontologia, Facultad de
Ciencias, Universidad de Extremadura, Avenida de Elvas s/n,
06006 Badajoz, Spain.
C.E. White. NS Department of Natural Resources, P.O. Box 698,
Halifax, NS B3J 2T9, Canada.
S.M. Barr. Department of Earth and Environmental Science,
Acadia University, Wolfville, NS B4P 2R6, Canada.
Corresponding author: Teodoro Palacios (e-mail:
[email protected]).
1This
article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.
Can. J. Earth Sci. 49: 289–307 (2012)
ided, from base to top, into the Eskasoni, Dugald, and
Gregwa formations (Hutchinson 1952; White et al. 1994).
The Dugald Formation contains middle Cambrian brachiopods and trilobites (Walcott 1912, p. 133; Hutchinson 1952),
and the Bourinot Group has been considered to be early middle Cambrian in its entirety (Hutchinson 1952; Landing
1996). The Bourinot Group is overlain by the more sandstone-rich MacMullin Formation, from which Middle Cambrian trilobites have been recorded, and locally by the
Furongian MacNeil Formation, consisting largely of dark
shale (Hutchinson 1952; White et al. 1994).
The relationship of the Bourinot Group to other Cambrian
successions in the vicinity, such as that in the Mira River
area to the southeast, has long been controversial. The controversy arises because the Bourinot Group lacks obvious
correlative units in the Mira River area, particularly in that
equivalents of the volcanic Eskasoni and Gregwa formations
are missing. There are also differences in the basement on
which these successions rest (e.g., Barr et al. 1998). These
differences have been explained either by the successions in
the Bourinot belt and Mira River area having developed on
different terranes (e.g., White et al. 1994; Barr et al. 1998)
or as regional differences within a common terrane (e.g.,
Landing 1996). Successions west of Mira River have been
doi:10.1139/E11-010
Published by NRC Research Press
290
Fig. 1. Simplified geological map showing the extension and geological context within the Bras d’Or terrane of Cambrian volcanic and
sedimentary strata of the Bourinot belt (grey shading) in central
Cape Breton Island, Nova Scotia, based on White et al. (1994,
fig. 1). Dashed lines are faults. Heavy Black line is the inferred Bras
d’Or (Ganderia) – Mira (Avalonia) terrnae boundary. Inset map
shows location (rectangle) and context of study area with respect to
Ganderia and Avalonia. BHr, Beaver Harbour; MRr, Manuels River.
Devon.–Carbon., Devonian to Carboniferous; Neoprot., Neoproterozoic.
proposed to provide lithostratigraphic similarities to the
Bourinot Group with the presence of basalt and rhyolite (e.g.,
Landing 1996), but other studies have shown that Cambrian
volcanic rocks are not present in that area (Barr et al.
1996).
In this paper, we present the first data on organic-walled microfossils from Cambrian strata in the Bourinot belt. The material is well-preserved and includes numerous age-diagnostic
taxa, which enable comparison with acritarch-based zones
established in other areas. Particular emphasis is made here
on the comparison to the Mira terrane (Palacios et al. 2009)
and to acritarch-based zones developed in southeastern
Newfoundland (Martin and Dean 1981, 1983, 1984, 1988)
and Spain (Palacios 2008, 2010; Palacios et al. 2006). No
evidence is known for provincialism in the distribution of
Cambrian acritarchs (e.g., Moczydłowska 1998, p. 38). For
example, Cambrian strata of Baltica, and many of the periGondwanan terranes, now spread across eastern North
America and southern Europe (i.e., approximating the
Acado-Baltic faunal province; see for example Cowie 1971;
Can. J. Earth Sci., Vol. 49, 2012
Sdzuy 1972) and have been the focus of numerous studies
of organic-walled microfossils with a generally uniform distribution of taxa (e.g., Palacios et al. 2009). Thus, while the
assemblages of organic-walled microfossils described here
do not yield new insights into the provenance and tectonic
evolution of the Bourinot belt, they enable more secure
temporal correlation of the Cambrian sequence of the Bourinot belt to other regions. The material described also includes occurrences of little reported taxa and expands the
known geographical distribution of many taxa. Much of the
results refer to strata belonging to Cambrian series 3, the
base of which has not been formally defined. In the text,
we therefore largely maintain the traditional usage of
Lower/Early Cambrian and Middle Cambrian.
Regional geology
The Bourinot belt is located in the southern part of the
Bras d’Or terrane of somewhat controversial relation to other
peri-Gondwanan terranes but generally considered to be part
of Ganderia (e.g., Barr et al. 1998; Hibbard et al. 2006). The
Cambrian volcanic–sedimentary succession, consisting of the
Bourinot Group and overlying MacMullin and MacNeil formations, is in faulted contact with older plutonic and metamorphic units. The basal unit of the Bourinot Group is the
Eskasoni Formation, which consists largely of bimodal volcanic rocks, with compositions indicative of formation in an
intra-continental rift-system (White et al. 1994). Its base is
not known. The Northern Boisdale Hill volcanic unit of
White et al. (1994) is also included here in the Eskasoni Formation. White et al. (1994) placed it in a separate unit because its U–Pb (zircon) age of 505 ± 3 Ma (Late Cambrian
according to the time scale of Palmer 1983) appeared to be in
conflict with the Middle Cambrian age of the Bourinot
Group based on fossil evidence. However, that apparent conflict no longer exists because in the current time scale, 509
Ma is in the middle part of the Cambrian (e.g., Walker and
Geissman 2009).
The Dugald Formation consists of siltstone with minor
sandstone and wacke, and also contains tuffaceous layers.
White et al. (1994) observed that its contact with the Eskasoni Formation is everywhere faulted. The Dugald formation
locally contains abundant and diverse inarticulate brachiopods, including Acrothele prima Matthew, 1886 and Acrotreta gemmula (Matthew, 1894) (e.g., Matthew 1903;
Walcott 1912). Other fossils include bradorids described in a
series of papers by Matthew (e.g., Matthew 1903). In a recent revision, Siveter and Williams (1997) recognized Bradoria scrutator Matthew, 1899 and Indiana lippa Matthew,
1902, as the only legitimate species among those described
from the Dugald Formation. Scarce trilobite material is
known from the upper part of the Dugald Formation, consisting of Solenopleura bretonensis Matthew, 1903 and Andrarina linnarssoni bretonensis Hutchinson, 1952. The
assemblage of brachiopods in the Dugald Formation has
been considered Middle Cambrian (Walcott 1912), and the
trilobites indicative of an early Middle Cambrian age (Hutchinson 1952).
The uppermost unit of the Bourinot Group, the Gregwa
Formation, consists of lithic tuff and minor siltstone, shale,
and volcanogenic conglomerate. No fossils have been reported from this formation. The overlying MacMullin FormaPublished by NRC Research Press
Palacios et al.
291
Fig. 2. Location of samples processed for organic-walled microfossils in the (A) southern and (B) northern parts of the Bourinot belt. Also
shown are the locations of trilobite localities described in Hutchinson (1952). The geological maps are based on White et al. (1994, fig. 2).
The stars show locations of samples dated by White et al. (1994).
tion consists of interbedded micaceous siltstone, sandstone,
and shale, locally with carbonate nodules. Trace fossils are
common, and early Middle Cambrian trilobites have been reported from several localities (Hutchinson 1952). The MacNeil Formation is dominated by black shale. It yields
Furongian (late Cambrian) trilobites and brachiopods (Hutchinson 1952).
Sample material and methods
The material studied here was collected by the authors in
2008 and 2009. The approximate sample locations are shown
on Fig. 2, together with their stratigraphic context as established on the basis of earlier mapping by White et al.
(1994). Specific sample locations and characteristics are summarized in Table 1.
From the collected material, rock samples of ca. 50 g were
treated with standard palynological methods, mounted on
glass slides with PetroPoxy resin, and studied under transmitted light with a ZeissAxio Imaginer M1 microscope with a
computerized Axiocam Hrc microcamera. Figured and representative material are stored with the collections of the Nova
Scotia Museum of Natural History, Halifax, Nova Scotia
(numbers NSM010GF041.001–NSM010GF041.025).
Organic-walled microfossils in the Bourinot Group and
MacMullin Formation
The majority of the collected samples yielded organicwalled microfossils. Three samples were barren (Bo09:4,
Bo09:14, Bo09:20), and one sample yielded only filaments
(Bo09:16) (Figs. 4C, 4D). The assemblages of acritarchs in
the positive samples are discussed in approximate stratigraphic order, starting with the lowest sample. A comprehensive list of the taxa identified is given in Fig. 3.
Sample Bo09:21 (Figs. 4A, 5A, 5C, 5E, 5F, 6G) is from
an isolated outcrop of micaceous siltstone and volcaniclastic
material, in an area with heavy cover by soil and vegetation.
White et al. (1994) identified a tectonic contact between the
Eskasoni and Gregwa formations in this area, with the Dugald Formation faulted out. The assemblage of acritarchs suggests that this sample is the oldest in this study, and it likely
represents sedimentary intervals in the uppermost part of the
Eskasoni Formation. Of particular note for the age of the
292
Table 1. Samples studied for organic-walled microfossils in the Bourinot belt, Cape Breton Island.
Sample No.
Lithology
Eskasoni Formation
Bo09:20
Cleaved siltstone
Bo09:21
Grey micaceous siltstone in interval with
volcaniclastic material
Dugald Formation
Bo09:7
Green laminated micaceous siltstone
Bo09:8
Grey laminated siltstone, with brachiopods
Bo09:13
Grey-green micaceous siltstone
Bo09:14
Green siltstone
Bo09:15
Green siltstone
Bo09:16
Dark grey shale
Bo09:17
Green siltstone
Bo09:18
Grey shale, with brachiopods
Bo09:19
Green micaceous siltstone
MacMullin Formation
Bo09:1
Green mudstone
Bo09 2
Green mudstone
Bo09:3
Grey mudstone between flags
Bo09:4
Green siltstone
Bo09:5
Green siltstone
Bo09:6
Green siltstone
Bo09:9
Grey mudstone in heterolithic interval
Bo09:10
Grey mudstone in heterolithic interval
Bo09:11
Grey micaceous siltstone from interval, with
carbonate nodules
Geo08:1.
Grey micaceous siltstone, heterolithic interval
Geo08:2
Geo08:3.
MacNeil Formation
Bo09:12
Dark shale with agnostid trilobites
Location (easting, northing in m)
a
Palynological slideb
see Fig. 2A
687110, 5094327
001 (barren)
002, 003
686051, 5092601
686051, 5092601
687882, 5095294
Ca. 100 m upstream
Ca. 120 m upstream
Ca. 150 m upstream
Ca. 170 m upstream
Ca. 200 m upstream
687915, 5095449
004
005
006
023 (barren)
007
008 (barren)
009
010
011
686207,
686207,
686203,
686178,
686178,
686154,
687635,
687635,
687734,
5092481
5092481
5092511
5092531
5092531
5092554
5094401
5094401
5094575
of
of
of
of
of
sample
sample
sample
sample
sample
13
13
13
13
13
012
013
014
No organic residue
015
016, 017
018
019
020
700114, 5116501
701679, 5119389
701679, 5119389
021
022
024
688097, 5094717
025
a
Universal Transverse Mercator Zone 20T.
Nova Scotia Museum of Natural History, Halifax, N.S., NSM010GF041.xxx.
b
sample is the occurrence of Eliasum llaniscum Fombella,
1977, Heliosphaeridium notatum (Volkova) Moczydłowska,
1998 (Fig. 5A), and Retisphaeridium dichamerum Staplin,
Jansonius and Pockock, 1965. This sample also contains
poorly preserved material of Skiagia sp. (close to Skiagia cf.
insignis of Downie 1982; Figs. 5E, 5F). The stratigraphically
lowest occurrence of Eliasum llaniscum on a global scale is
close to the traditional Lower–Middle Cambrian transition
(Moczydłowska 1998). In Newfoundland, the lowest occurrence of Eliasum llaniscum is ca. 5 m above the base of the
Chamberlains Brook Formation in strata assigned to the Paradoxides bennetti Zone. Heliosphaeridium notatum is common in strata assigned to the Protolenus Zone and the
Paradoxides oelandicus Superzone on Baltica, and equivalent
levels in Spain (Palacios and Moczydłowska 1998). The
combined evidence suggests that this sample has a position
close to the base of Cambrian series 3.
Samples Bo09:17, Bo09:18, and Bo09:19 (Figs. 4B, 5B,
5D, 5G, 8A, 8B) were collected from the lower part of the
Dugald Formation on Dugald Brook. In common with sample 21, they contain Eliasum llaniscum and Retisphaeridum
dichamerum (Figs. 8A, 8B). In addition, there are Comasphaeridium silesiense Moczydłowska, 1998 (Fig. 5B; in sample 17) and Heliosphaeridium serridentatum Moczydłowska,
1998 (Fig. 5D; in samples 17 and 18). Comasphaeridium silesiense has been considered to have a first appearance close
to the base of the Middle Cambrian (Moczydłowska 1999). It
was described from the middle Cambrian (oelandicus Superzone) of Silesia (Moczydłowska 1998), and it is also known
from coeval strata in Sweden. Heliosphaeridium serridentatum was described from the middle Cambrian (oelandicus
Superzone) of Silesia (Moczydłowska 1998). Sample 18 contains a form that Martin and Dean (1984) reported as “Acritarch gen. and sp. nov” from the upper part of Chamberlains
Brook Formation and lower part of the Manuels River Formation in Newfoundland. Acritarch gen. and sp. nov. is one
of the name-bearing forms for Microflora A0-1 (Eliasum jennessi and Acritarch gen. et sp. nov. assemblage) in Newfoundland, though it ranges into the Rugasphaera
terranovana and Adara alea zones (Martin and Dean 1988).
Additional common taxa of this zone are Retisphaeridum dichamerum and Eliasum llaniscum, both with relatively long
stratigraphic ranges. In Spain, the IMC1 Zone is characterized by the presence of Comasphaeridium silesiense, Eliasum
llaniscum, and Acritarch gen. and sp. nov. (Palacios 2008).
The acritarchs from samples Bo09:17, Bo09:18, and
Bo09:19, suggest correlation with assemblage A0-1 in Newfoundland and the upper part of the IMC1 Zone in Spain.
The absence of Cristallinium cambriense argues against correlation with the Rugasphera terranovana Zone in Newfoundland and the IMC2 Zone in Spain. The A0-1
assemblage corresponds to the eteminicus Zone, though it
Palacios et al.
293
Fig. 3. Chart summarizing the distribution of organic-walled microfossils in the samples examined in this study. St. And., St. Andrews Channel.
may extend to the bennetti Zone, as this zone is poorly characterized by acritarchs in Newfoundland.
Samples Bo09:7 and Bo09:8 (Figs. 6B, 6D–6F), from the
Dugald Formation in Gregwa Brook, contain several specimens in common with samples Bo09:17 and Bo09:18, notably Acritarch gen. et sp. nov. (Figs. 6D, 6E), and Eliasum
llaniscum (Fig. 6B). Sample 8 additionally contains Abacum
normale Fombella, 1978 (Fig. 6F), a taxon known from the
Oville Formation of northern Spain, where it has a long
stratigraphical range (IMC2–IMC5 zones, Palacios 2010),
and assemblage BB1 in the Booley Bay Formation of Ireland
(Vanguestaine and Brück 2008).
The acritarchs from samples Bo09:7 and Bo09:8, suggest
correlation with assemblage A0-1 in Newfoundland and the
upper part of the IMC1 Zone in Spain. The absence of Cristallinium cambriense argues against correlation with the Rugasphaera terranovana Zone. However, the presence of
Abacum normale could indicate correlation with the IMC2
Zone, or higher in Spain, although the absence in the assemblage of other diagnostic taxa of this zone may instead suggest an extended lower range of Abacum normale.
Sample Bo09:15, from the upper part of the Dugald Formation on Dugald Brook, contains a low diversity of acritarchs, which includes Multiplicisphaeridium parvum
294
Fig. 4. Organic-walled microfossils from the uppermost part of the Eskasoni Formation (A), and the Dugald Formation (B–D), Dugald Brook
area. In this and the following figures are given the sample number, museum number, and England finder coordinates. Scale bar = 20 mm in
(A, B) and 40 mm in (C, D). (A, B) aff. Sagatum priscum (Kir'yanov and Volkova) Vavrdová and Bek, 2001. (A) Bo09:21;
NSM010GF041.002/A; B-35-1. (B) Bo09:17; NSM010GF041.009/A; A-27-4. (C, D) Filaments. (C) Bo09:16; NSM010GF041.008/A; O-24.
(D) Bo09:16; NSM010GF041.008/B; B-27-1.
Palacios et al.
295
Fig. 5. Acritarchs from the uppermost part of the Eskasoni Formation (A, C, E, F), and the Dugald Formation (B, D, G), Dugald Brook area.
Scale bar = 20 mm. (A) Heliosphaeridium notatum (Volkova) Moczydłowska, 1991. Bo09:21; NSM010GF041.003/A; R-26-3. (B) Comasphaeridium silesiense Moczydłowska, 1998. Bo09:17; NSM010GF041.009/B; B-30-4. (C) Comasphaeridium sp. Bo09:21;
NSM010GF041.002/B; A-18-4. (D) Heliosphaeridium serridentatum Moczydłowska, 1998. Bo09:17; NSM010GF041.009/C; H-25-3. (E, F)
Skiagia sp. (E) Bo09:21; NSM010GF041.002/C; H-44-1. (F) Bo09:21; NSM010GF041.003/B; E-23. (G) Solisphaeridium implicatum (Fridrichsone) Moczydłowska, 1998. Bo09:17; NSM010GF041.009/D; Y-33-1.
(Hagenfeldt) Moczydłowska, 1998, a species with heteromorphic processes (simple to branching) with a length about
equal to the vesicle diameter. This species was first described
from beds attributed to the oelandicus Superzone in Sweden
(Hagenfeldt 1989). Multiplicisphaeridium parvum also occurs
in the Nant-y-big Formation on the St. Tudwal’s Peninsula,
where it was reported as Heliosphaeridium? llynense (Young
et al., 1994) in beds attributed to the Tomagnostus fissus
Zone (equivalent to the hicksi Zone, Fletcher 2007). Timofeevia tacheddirtensis Vanguestaine and van Looy, 1983, from
Morocco is here considered to be flattened specimens of M.
parvum. In Morocco, M. parvum occurs with Cristallinium
cambriensis and Adara alea Martin in Martin and Dean,
1981 (Celtiberium cf. geminum in Vanguestaine and van
Looy 1983, pl. 1, figs. 5, 6), suggesting correlation with the
Adara alea Zone (and IMC3). The acritarchs in sample
Bo09:15 do not provide fine biostratigraphical control.
Sample Bo09:13 (Figs. 6A, 6C, 7A–7F, 8C) from the Dugald Formation on Dugald Brook contains Multiplicisphaeridium parvum (Fig. 7), and several species diagnostic of the
Rugasphera terranovana Zone (= Zone A0) in Newfoundland, corresponding to the hicksi Zone, with the appearance
of Cristallinium cambriense (Fig. 8C) and Vulcanisphera lanugo (Fig. 6C) (Martin and Dean 1984, 1988). In northern
Spain, the corresponding zone IMC2 has the first appearance
of Cristallinium cambriense and is defined on the stratigraphic range of V. lanugo (Palacios 2008). Vulcanisphaera
lanugo was originally described from the lower part of the
296
Fig. 6. Acritarchs from the uppermost part of the Eskasoni Formation (G), and the Dugald Formation (A–F), Grewa Brook and Dugald
Brook. Scale bar = 20 mm. (A) Eliasum asturicum Fombella, 1977. Bo09:13; NSM010GF041.006/A; B-44-2-4. (B) Eliasum llaniscum Fombella, 1977. Bo09:7; NSM010GF041.004/A; V-44-1. (C) Vulcanisphaera lanugo Martin in Martin and Dean, 1988. Bo09:13;
NSM010GF041.006/B; C-41-4. (D, E) Acritarch gen. et sp. nov. Martin in Martin and Dean, 1984. (D) Cluster with several specimens.
Bo09:7; NSM010GF041.004/B; Q-35-2. (E) Isolated specimen. Bo09:7; NSM010GF041.004/C; D-31-3. (F) Abacum normale Fombella,
1978. Bo09:8; NSM010GF041.005/A; E-38-1. (G) Granomarginata squamacea Volkova, 1968. Bo09:21; NSM010GF041.002/D; C-33.
Palacios et al.
297
Fig. 7. Acritarchs from the upper part of the Dugald Formation, Dugald Brook. Scale bar = 20 mm. (A–F) Multiplicisphaeridium parvum
(Hagenfeldt) Moczydłowska, 1998. (A) Bo09:13; NSM010GF041.006/C; B-46-3. (B) Bo09:13; NSM010GF041.006/D; C-44. (C) Bo09:13;
NSM010GF041.006/E; F-36-2. (D) Bo09:13; NSM010GF041.006/F; K-28. (E) Bo09:13; NSM010GF041.006/G; T-15-1. (F) Bo09:13;
NSM010GF041.006/H; S-15-1-2.
298
Fig. 8. Acritarchs from the Dugald (A–C) and McMullin (D–F) formations, Gregwa Brook and Dugald Brook. Scale bar = 20 mm. (A, B)
Retisphaeridium dichamerum Staplin, Jansonius and Pocock, 1965. (A) Bo09:17; NSM010GF041.009/E; L-24. (B) Bo09:17;
NSM010GF041.009/F; J-31-1-3. (C, D) Cristallinium cambriense (Slaviková, 1968) Vanguestaine, 1978. (C) Bo09:13; NSM010GF041.006/I;
J-42-3. (D) Bo09:3; NSM010GF041.014/A; K-36-4. (E, F) Cristallinium dubium Volkova, 1990. (E) Bo09:6; NSM010GF041.016/A; S-47.
(F) Bo09:6; NSM010GF041.017/A; E-32-4.
Palacios et al.
Manuels River Formation, where it is restricted to the middle
part of the hicksi Zone (Martin and Dean 1988). V. lanugo is
also known from the lower part of the Playon Formation in
southern Spain (Palacios et al. 2006) and the lower part of
the Oville Formation of the Cantabrian Mountains, northern
Spain, where it is associated with Eliasum asturicum Fombella, 1977, Cristallinium cambriense and Celtiberium dedalinum Fombella, 1978, in the Badulesia Zone (Palacios 2008,
2010). Vanguestaine and Brück (2008) reported V. lanugo
from their BB1 assemblage of the Booley Bay Formation of
Ireland, which they concluded to span the Ptychagnostus atavus, Hypagnostus parvifrons, and Ptychagnostus punctuatus
zones, opening the possibility that the stratigraphic position
of the Irish V. lanugo is somewhat higher than in Newfoundland. However, this occurrence is apparently based on a single specimen (Vanguestaine and Brück 2008, pl. 3, fig. 7),
which has a morphology similar to Vulcanisphaera spinulifera. Eliasum asturicum (Fig. 6A) spans the IMC2 and
IMC3 zones in northern and southern Spain (Palacios 2008).
Sample Bo09:13 can be confidently correlated with the lower
part of the Manuels River Formation and a relatively confined interval within the hicksi Zone, or more generally with
zone IMC2 in Spain.
Samples Bo09:1, Bo09:2, Bo09:3, Bo09:5, and Bo09:6
(Figs. 8D–8F, 9A–9F, 10A–10C, 11A, 11B, 11E, 11H, 11K,
11L), from the lower part of the MacMullin Formation on
Gregwa Brook, contain a diverse assemblage of acritarchs,
with the occurrence of Aranidium granulatum Welsch, 1986
(Fig. 11E), Cristallinium dubium Volkova, 1990 (Figs. 8E,
8F), Symplassosphaeridium cambriense Slaviková, 1968
(Figs. 10A, 10B), Timofeevia lancarae (Cramer and Diez)
Vanguestaine, 1978 (Figs. 9A, 9B), T. microretis Martin in
Martin and Dean, 1983 (Figs. 11A, 11B), T. phosphoritica
Vanguestaine, 1978, T. sp. A (Figs. 9C, 9D), T. sp. B
(Figs. 9E, 9F), and Tubulosphaera sp. (Fig. 10C). The presence of A. granulatum in the MacMullin Formation is of particular interest. Aranidium granulatum has a polygonal to
spherical vesicle with a circular pylome, and processes with
conical bases. In northern Norway, this form is restricted to
assemblage AI, occurring with, among others, Cristallinium
ovillense, and a diverse assemblage of small acanthomorphic
acritarchs (Welsch 1986). The AI assemblage lies within the
Paradoxides paradoxissiumus Superzone and underlies a trilobite assemblage attributed to the Ptychagnostus puntuosus
Zone (Nikolaisen and Henningsmoen 1990). A similar assemblage from the upper part of the paradoxissimus Superzone defines the SK2a Zone in the East European Platform
(Volkova and Kir’yanov 1995), which contains several species of Aranidium and which precedes levels with the first
Cristallinium dubium and various species of Timofeevia. The
first occurrence of A. granulatum and Cristallinium dubium
in northern Spain is in the upper part of the IMC5 Zone (Palacios 2008, 2010). Symplassosphaeridium cambriense, found
in samples Bo09:5 and Bo09:6 occurs with Tubulosphaera
sp. in the Oville Formation, northern Spain, a short stratigraphical distance below an occurrence of Paradoxides cf.
davidis (Sdzuy 1961) in the lower part of IMC5 Zone (Palacios 2008, 2010). In the Mira River area, S. cambriense occurs with C. dubium in an interval that contains Paradoxides
davidis (Palacios et al. 2009). Samples Bo09:1, Bo09:2,
Bo09:3, Bo09:5, and Bo09:6, contain diverse species of Tim-
299
ofeevia. However, the identification and stratigraphic range of
several species of Timofeevia need restudy (cf. Palacios et al.
2009). For example, specimens of Timofeevia lancarae, figured by Martin and Dean (1981, 1988) from Newfoundland
and Welsch (1986) from northern Norway, do not correspond
to the type material of this species illustrated by Cramer and
Diez (1972). The specimens here identified as T. lancarae
(Figs. 9A, 9B) are only those materials that share diagnostic
characteristics with the type specimens described by Cramer
and Diez (1972) from the Oville Formation in the type area
in the Cantabrian Mountains, northern Spain. Timofeevia sp.
A (Figs. 9C, 9D) is a species with short conical processes.
Identical forms have been referred to in the literature as T.
phosphoritica, T. manata, and T. janishewskyi, for example
from the Sosinsk Formation by Dean et al. (1997; Figs. 9A,
9B). However, the type material of T. phosphoritica and T.
manata have tubular processes, and T. phosphoritica exhibits
rupture into paraplates. Timofeevia sp. B (Figs. 9E, 9F) is
distinguished from T. lancarae by a greater number of processes. In northern Spain, T. sp. B, has a long stratigraphic
range (IMC4–IMC6; Palacios, unpublished observations).
These two forms of Timofeevia represent new species that
will be formally described in a future publication. The assemblage of acritarchs in these samples suggest correlation with
the IMC5 Zone in Spain.
Samples Bo09:9, Bo09:10, and Bo09:11 (Fig. 11C) from
the MacMullin Formation on Indian Brook contain relatively
poorly preserved acritarchs, but the combined presence of
Timofeevia lancarae, T. phosphoritica (Fig. 11C), Cristallinium cambriense, C. dubium, and Symplassosphaeridium
cambriense indicates correlation with the IMC5 Zone in
Spain and is closely comparable to the assemblage of acritarchs found close to the transition between the Trout Brook
and MacLean Brook formations in the Mira River area (Palacios et al. 2009), with a position close to the transition between the Paradoxides davidis and Paradoxides
forchhammeri zones. The samples from the MacMullin Formation are indicative of the upper part of the davidis Zone,
to the lower part of the forchhammeri Zone.
Samples Geo08:1, Geo08:2, and Geo08:3 (Figs. 11D, 11F,
11G, 11I, 11J) from the MacMullin Formation in the northern part of the Bourinot Belt include taxa also reported from
the middle and upper part of the MacLean Brook Formation
in the Mira River area, such as Stelliferidium magnum Palacios in Palacios et al., 2009 (Fig. 11F) and Petaloferidum lacrimiferum Palacios in Palacios et al., 2009 (Figs. 11I, 11J)
(Palacios et al. 2009 and unpublished observations). This assemblage indicates correlation with the IMC6 Zone in Iberia,
which is characterized by the first appearance of Stelliferidium magnum, Timofeevia microretis, and T. phosphoritica
(Palacios 2010).
Discussion
Age of the Bourinot Group and MacMullin Formation
The assemblages of acritarchs described in the preceding
section provide new constraints for the age of the Bourinot
Group and MacMullin Formation (Fig. 12). The most specific pronouncements on these Cambrian strata are those of
Hutchinson (1952), Landing (1996, p.43, fig. 5), and LandPublished by NRC Research Press
300
Fig. 9. Acritarchs from the McMullin Formation, Gregwa Brook. Scale bar = 20 mm. (A, B) Timofeevia lancarae (Cramer and Díez, 1972)
Vanguestaine, 1978. (A) Bo09:6; NSM010GF041.016/B; K-34-4. (B) Bo09:3; NSM010GF041.014/B; M-15. (C, D) Timofeevia sp. A. (C)
Bo09:3; NSM010GF041.014/C; B-34–3. (D) Bo09:6; NSM010GF041.017/B; T-32-4. (E, F) Timofeevia sp. B. (E) Bo09:6;
NSM010GF041.016/C; A-32-3-4. (F) Bo09:6; NSM010GF041.017/C; L-21-2-4.
Palacios et al.
301
Fig. 10. Acritarchs from the McMullin Formation, Gregwa Brook. Scale bar = 20 mm. (A, B) Symplassosphaeridium cambriense Slaviková,
1968. (A) Bo09:6; NSM010GF041.017/D; E-52-4. (B) Bo09:6; NSM010GF041.017/E; V-15. (C) Tubulosphaera sp. Bo09:6;
NSM010GF041.016/D; C-33-1-3.
ing and Westrop (1998, fig. 20). Landing (1996) assigned the
Dugald Formation to the Hartella bucculenta Zone (= Paradoxides eteminicus Zone), with the Eskasoni Formation occupying the upper part of the bennetti Zone, the Gregwa
Formation assigned to the hicksi Zone, and the MacMullin
Formation spanning the top of the hicksi Zone to the Homagnostus obesus Zone. This largely coincides with the age assignments given by Hutchinson (1952), except that he
restricted the MacMullin Formation to the hicksi Zone. Landing’s (1996) extended range for the upper part of the MacMullin Formation was on the assumption that it is equivalent
to the MacLean Brook Formation in the Mira River area.
Landing (1996, p. 43) suggested that the volcanic rocks of
the Eskasoni Formation correlate with volcanic rocks in the
Chamberlains Brook Formation at Trinity Bay, southeastern
Newfoundland. The data from acritarchs presented here
largely support these assignments, but also leaves open the
possibility that the Eskasoni Formation includes older volcanic rocks, and it brings into question the age of trilobitebearing portions of the MacMullin Formation.
Highly relevant to the age question of the Eskasoni Formation are the published U–Pb (zircon) dates from the northern
part of the Bourinot belt. Rhyolite on Long Island likely belonging to the Eskasoni Formation yielded an age of 505 +/–
3 Ma (White et al. 1994). A syenogranite sample from the
nearby Mount Cameron pluton yielded an age of 509 +/– 2
Ma. Petrological similarities suggest that the rhyolite and syenogranite are likely co-magmatic and their U–Pb ages overlap
within error. These ages of 509–505 Ma are close to recent
estimates for the base of Cambrian series 3 at ca. 510 Ma
(Fig. 12). Hutchinson (1952) inferred the transition between
the Eskasoni and Dugald formations to be gradual because
of shale intervals in the Eskasoni Formation with early Middle Cambrian brachiopods comparable to those in the Dugald
302
Fig. 11. Acritarchs from the McMullin Formation, Gregwa Brook, Indian Brook, and St. Andrews Channel areas. Scale bar = 20 mm. (A, B)
Timofeevia microretis Martin in Martin and Dean, 1983. (A) Bo09:3; NSM010GF041.14/D; E-43-2. (B) Bo09:5; NSM010GF041.015/A; A16-2. (C, D) Timofeevia phosphoritica Vanguestaine, 1978. (C) Bo09:9; NSM010GF041.018/A; H-36-3. (D) Geo08-3; NSM010GF041.024/
A; C-21-2. (E) Aranidium granulatum Welsch, 1986. Bo09:3; NSM010GF041.014/E; J-38. (F) Stelliferidium magnum Palacios in Palacios et
al., 2009. Geo08:1; NSM010GF041.021/A; C-15-1. (G) Stelliferidium albanii Palacios in Palacios et al., 2009. Geo08:1; NSM010GF041.021/
B; U-32-2. (H) Solisphaeridium flexipilosum (Slaviková, 1968) Moczydłowska, 1998, Bo09:5; NSM010GF041.015/B; G-41. (I, J) Petaloferidium lacrimiferum Palacios in Palacios et al., 2009. (I) Geo08:2; NSM010GF041.022/A; D-24-4. (J) Geo08:1; NSM010GF041.021/C; C-232-4. (K, L) Heliosphaeridium lanceolatum (Vanguestaine) Moczydłowska, 1998. (K) Bo09:5; NSM010GF041.015/C; S-39-3. (L) Bo09:5;
NSM010GF041.015/D; A-33-1.
Formation. Although its position is somewhat uncertain because it is from an isolated outcrop, it is probable that sample
Bo09: 21 is from such a shaly interval near the top of the
Eskasoni Formation. A sample (Bo09:20) of cleaved siltstone
from the upper part of the Eskasoni Formation along Dugald
Brook was processed for organic-walled microfossils but
found barren. The combined data from geochronology and
acritarchs suggest that the Eskasoni Formation extends to at
least the lower part of Cambrian stage 5 (Fig. 12), but the
base of the formation is not known. Landing et al. (2008,
p. 889) cited Barr et al. (1996) for a U–Pb date of ca. 522
Ma for the lower part of the Eskasoni Formation, but no
such data were presented in that publication, and hence the
validity of the 522 Ma date is uncertain.
The acritarch assemblage from the lower part of the Dugald Formation agrees with Landing’s (1996) assignment to
the eteminicus Zone (although not excluding the possibility
that it enters the bennetti Zone) and temporal correlation to
the upper part of the Chamberlains Brook Formation. However, the highest sample in the Dugald Formation on Dugald
Brook contains an assemblage clearly correlated with the
hicksi Zone. This sample has a position close to the Dugald–
Gregwa transition. Of particular note is the presence in this
sample of Vulcanisphaera lanugo, also known from the
lower part of the Manuels River Formation in Newfoundland.
A scarce trilobite faunule was reported 3.6 m below the Dugald–Gregwa contact on Dugald Brook, comprising Solenopleura bretonensis and Andrarina linnarssoni bretonensis
(Matthew 1903; Hutchinson 1952; Geological Survey of
Canada (GSC) 18583 on Fig. 2). Neither of these taxa has
been reported outside of the area. Hutchinson (1952) remarked that Solenopleura rushtonensis Cobbold, 1934, from
the Upper Comley Sandstone of Shropshire, England, may be
a junior synonym of Solenopleura bretonensis, and Landing
(2006, p. 43) built on this suggestion, when he used the cooccurrence of Solenopleura rushtonensis with Ptychagnostus
gibbus as evidence to assign the Dugald Formation to the
Hartella bucculenta Zone. Rushton et al. (2007, p. 137), on
the other hand, rejected the synonymy of Solenopleura bretonensis and S. rushtonensis. The precise stratigraphic position
of the acritarch sample relative to the trilobite-bearing horizon is not known but is assumed to approximate it. Based
on the assemblage of acritarchs, the upper part of the Dugald
Formation extends to the hicksi Zone and correlates temporally with the lower part of the Manuels River Formation.
Hutchinson (1952) interpreted the lower contact of the
MacMullin Formation to represent a disconformity in its
northern area of exposure in the Bourinot belt because of
greatly reduced thickness, although this may also be the result of faulting (White et al. 1994). In the Indian Brook area
the contact has been interpreted as being conformable,
although the contact is generally poorly exposed (Hutchinson
1952, pp. 24–25). Acritarchs from the lower part of the MacMullin Formation on Gregwa Brook suggest correlation with
strata close to the transition of the davidis and forchhammeri
zones, or in the forchhammeri Zone. Comparison with the acritarch record from Newfoundland in much of the davidis and
forchhammeri zones is complicated because of poor preservation, intervals with missing data, and a likely hiatus that may
span a substantial part of these zones in Newfoundland.
Hutchinson (1952, pp. 25–26) reported an assemblage of
trilobites from sandy shales of the MacMullin Formation on
Indian Brook (locality GSC 18572, see Fig. 2A), with Acrocephalops matthewi Hutchinson, 1952, Holasaphus centropyge Matthew, 1895, Cotalagnostus barrandei (= Lejopyge
barrandei), and Bailaspis sp., that he attributed to the hicksi
Zone, largely on account of the identification of Lejopyge
barrandei (Hicks, 1872). Lejopyge barrandei is known from
the lower part of the Manuels River Formation at Manuels
River (Howell 1925; Landing and Westrop 1998; Fig. 7),
where it occurs in the hicksi Zone, including the bed that
yields the main record of Vulcanisphaera lanugo (bed 51 of
Howell 1925). Howell’s (1925) highest citation of Lejopyge
barrandei in the Manuels River section coincides with the
top of the Rugasphera terranovana Zone. The ages indicated
by acritarchs from the lower part of the MacMullin Formation on Gregwa Brook seem inconsistent with the reports of
hicksi Zone trilobites. Hutchinson (1952) noted that the contact between the Gregwa and MacMullin formations on
Grewa Brook is separated by a 30 cm thick zone of deeply
weather material of uncertain composition. This zone may indicate that the contact here is faulted and that the lowest part
of the MacMullin Formation is missing in this section. However, the succession of Cambrian strata between Gregwa
Brook and Dugald Brook is represented by a truncated inverted limb that is younging in a southeasterly direction
(White et al. 1994; Fig. 7A). The location of trilobite locality
GSC 18572 suggests that it belongs to a higher stratigraphic
interval than the acritarch samples on Gregwa Brook. It is
possible, therefore, that trilobites from locality GSC 18572
are younger than previously thought and that their identification needs to be revised. The record of Lejopyge barrandei in
this locality is based on a single poorly preserved cephalon
and is doubtful (P. Ahlberg, personal communication, 2010).
Acrocephalops matthewi and Holasaphus centropyge are both
unique to the MacMullin Formation. Dean (1972) described a
second species of Holasaphus, H. mesopotamicus from the
upper part of the Sosinsk Formation of Turkey. Holasaphus
mesopotamicus occurs in an interval that has yielded Timofeevia lancarae and forms transitional between T. lancarae
Palacios et al.
303
304
Fig. 12. Age constraints of acritarch assemblages on the Bourinot Group and MacMullin Formation indicated by the vertical extension of
rectangles, in relation to acritarch-based zones in Newfoundland (e.g., Martin and Dean 1988) and Spain (Palacios 2008, 2010). Correlation
between acritarch zones in Spain and Newfoundland is according to Palacios (2008, 2010). Alternative ages of trilobite assemblages in the
MacMullin Formation are (1) that given by Hutchinson (1952), and (2) a younger age here considered a likely possibility. Spain columns: 1,
lithostratigraphical units, Cantabrian Mountains, northern Spain; 2, lithostratigraphical units, Zafra area, southern Spain; 3, acritarch zones of
Palacios (2008, 2010). Newfoundland columns: 1, acritarch zones of Martin and Dean (1988); 2, lithostratigraphical units; 3, biozones (based
on Landing and Westrop 1998). Correlation between zones in Baltica (selected time interval only) and Newfoundland follows Geyer et al.
(2003). B. sc., Bradoria scrutator.
and T. phosphoritica (Dean et al. 1997). Both the acritarch
assemblage and relationship to other trilobites in the Sosink
Formation show that H. mesopotamicus is late middle Cambrian (Dean et al. 1997). Dean (1972, p. 277) remarked that
“The similarities between H. centropyge and H. mesopotamicus are sufficiently close to attempt one into postulating a
similar age for the 2 species, but the stratigraphical evidence
is not conclusive.” The data presented here on acritarchs support the possibility that Holasphus centropyge and H. mesopotamicus are coeval. It should also be noted that Dean
(1982) remarked on the strong resemblance to H. mesopotamicus of a cranidium from the basal portion of the Elliot
Cove Formation in beds of the Lejopyge laevigata Zone, in
the Manuels River section, that had been previously recorded
as Andrarina costata (Angelin, 1854).
A richer and better preserved trilobite assemblage has been
reported from the MacMullin Formation in the northern part
of the Bourinot belt in limestone concretions on the shore of
St. Andrews Channels (GSC 18570, Fig. 2B), where Holasaphus centropyge is recorded with Paradoxides abenacus Matthew, 1886, Acadagnostus acadicus Hartt, 1866, Ptychoparia
bretonensis Hutchinson, 1952, and Acrocephalops matthewi
(Hutchinson 1952). Hutchinson (1952) assigned this assemblage to the hicksi Zone. The identification of Acadagnostus
acadicus was considered questionable by Robison (1995),
thus making the identification of Paradoxides abenacus critical. Hutchinson (1952, p. 76) considered differences between the Cape Breton Island material and the type material
from New Brunswick to be the result of differences in preservation. Nevertheless, the lack of ridges on the front of the
glabella in the MacMullin Formation material suggests that
the assignment to P. abenacus is uncertain. In view of the
data presented here, a new look at the identification of the
MacMullin Formation Paradoxides is warranted. The acritarch assemblages recovered in the MacMullin Formation in
the northern part of the Bourinot belt come from outcrops
(Fig. 2B) that yield acritarchs of the forchhammeri Zone.
Landing (1996, p. 43) also noted hicksi Zone trilobites in
what he described as a Manuels River Formation-like tongue
of dark shale and limestone nodules in the lower MacMullin
Formation, but without giving any details on the taxa identified.
No acritarchs of the Adara alea Zone were recovered during this study. Adara alea has a narrow stratigraphic range in
all of its occurrences and may represent a short time interval.
In Newfoundland, the Adara alea range Zone (= A1 Zone
(Adara alea – Eliasum llaniscum assemblage)) spans the
upper part of the hicksi Zone in the Manuels River Formation
and questionably enters the davidis Zone. In Spain, IMC3 is
a corresponding zone defined on the range of Adara alea and
approximates the Pardailhania Zone of the middle Caesarau-
gustian. Also missing from the MacMullin Formation (and
from Newfoundland) are taxa characteristic of the IMC4
Zone of Spain, such as Adara matutina Fombella, 1977, Celtiberium geminum Fombella, 1977, and Timofeevia raquelinae (Cramer and Diez) Cramer and Diez, 1979 (Palacios
2010).
The data from acritarchs indicate that the possibility of a
disconformity at the base of the MacMullin Formation
(Hutchinson 1952) needs further consideration. Future sampling along trilobite-bearing strata at St. Andrews Channel
and Indian Brook, and on MacMullin Brook, which has the
best exposed transition between the Gregwa and MacMullin
formations in the Indian Brook area, may shed additional
light on the conflicting data from trilobites and acritarchs. A
sample from the MacNeil Formation on Indian Brook
(Bo09:12) was processed for organic-walled microfossils but
found to be barren.
Implications for the age of the British Acrothele prima
Shale
The Dugald Formation has been for long time a reference
for the age of the Acrothele prima Shale of the Wrekin area,
Shropshire, England. The Acrothele prima Shale is based on
material from a temporary excavation (Cobbold and Pocock
1934), and its placement within the regional stratigraphy has
been uncertain. Both the Dugald Formation and Acrothele
prima Shale contain the brachiopods Acrothele prima and
Acrotreta gemmula, and the bradorid arthropod Bradoria
scrutator. The Acrothele prima shale was long thought to be
Lower Cambrian following Ulrich and Bassler’s (1931) assignment of the Dugald Formation fossils to the Lower Cambrian, and attributed to the Lower Comley Sandstone. This
error was only recently corrected, and the Acrothele prima
Shale is now placed in the Middle Cambrian Upper Comley
Sandstone (Williams and Siveter 1998; Rushton et al. 2007).
Matthew (1903) described a great number of species of Bradoria from the Dugald Formation on Dugald Brook, but Siveter and Williams (1997) considered all to be synonyms of
Bradoria scrutator. In the section on Dugald Brook, Bradoria scrutator is known from Matthew’s (1903) divisions E1b
to E3f, thus spanning most of the Dugald Formation. Bradoria scrutator spans several of the acritarch samples examined
here (with certainty Bo09:17, Bo09:18, and Bo09:19), confirming earlier assignements of this bradorid to the eteminicus Zone, whereas the stratigraphically highest occurrences
may be in the hicksi Zone. Under the assumption of a similar
stratigraphical range for this species in its different occurrences, the data presented here on organic-walled microfossils
support the assignment of the Acrothele prima Shale to the
gibbus, or possibly fissus, Zone (Williams and Siveter 1998;
Rushton et al. 2007).
Palacios et al.
Regional context of the Bourinot Group
The data presented here on organic-walled microfossils
from the Bourinot belt provide tighter biostratigraphical age
control on the Cambrian sedimentary succession than was
previously available (Hutchinson 1952) and broadly support
the age relations suggested by Landing (1996, p. 43, fig. 5)
305
and Landing and Westrop (1998, fig. 20). Thus, volcanic
rocks of the Eskasoni Formation may be coeval with volcanism in the Chamberlains Brook Formation at Trinity Bay (but
could be older) and tuffaceous material in the Gregwa Formation with ash beds in the Manuels Rivers Formation.
Landing et al. (2008) reported Bradoria sp. cf. B. scrutator
306
from a Cambrian succession with abundant volcanic material
at Beaver Harbour, southern New Brunswick (Fig. 1, inset),
and considered this observation their best available biostratigraphical constraint on shales that follow upon volcanic rocks
of their Wades Lane Formation. We sampled the Cambrian
successions in the Beaver Harbour area for organic-walled
microfossils, but all samples were barren. However, if the
correlation potential of Bradoria scrutator is accepted, the
stratigraphic position of volcanic rocks in the Wades Lane
Formation is consistent with their being coeval with the Eskasoni Formation. Inferences on the proximity of these areas
on the basis of volcanic activity is problematic, as volcanic
activity was widespread along the northern margin of Gondwana during this period of time as part of rifting related to
the incipient stages in the opening of the Rheic Ocean (e.g.,
Pollock et al. 2009; Nance et al. 2010). For example, extensive deposits of pyroclastic rocks, and other volcanic material, including ignimbrite, formed in the same time period in
the transition from the Vallehondo to Playon formations in
the Ossa Morena Zone of southern Spain (e.g., Etxebarria et
al. 2006). As presently understood, acritarchs do not show
palaeogeographical differentiation in the Cambrian, and so
cannot help to resolve the relative positions of the various
peri-Gondwanan terranes. This study, however, is an additional example of the widespread distribution and biostratigraphical utility of acritarchs in the Cambrian series 3 across
a region broadly coinciding with the Acado-Baltic faunal
zone.
Acknowledgements
TP and SJ acknowledge funding from the Spanish Ministry
of Science and Innovation, through grant CGL-2008-04373
(co-financed by FEDER). SMB’s work in Cape Breton Island
is supported by a Discovery Grant from the Natural Sciences
and Engineering Research Council of Canada. We thank the
journal referees Paul Strother and Stewart Molyneux and Associate Editor Brendan Murphy for suggestions that improved
the manuscript. Museum numbers were provided by Deborah
Skilliter, Nova Scotia Museum of Natural History, Halifax, N.S.
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Cambrian acritarchs from the Bourinot belt, Cape Breton Island

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