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Chapter 49. Lower Carboniferous ostracode assemblages from Nova Scotia
C I Cumberland
Ma 1 Mabou
1-Location map of study area showing depositional sub-basins of Nova Scotia and sampling localities.
tion was neither continuous within, nor sychronous among the various sub-basins (Giles, 1981).
Inter-sub-basinal correlation has therefore been a matter of much debate; however, a mega-faunal
zonation (Bell, 1927, 1929) and formal lithostratigraphic subidivisions (Giles, et af., 1979; Giles,
1981) have been developed for the Windsor Group (Text-fig. 2). The stratigraphic relationships of
the Windsor Group with the upper Mississippian of the mid-continental U.S.A. and the Visean of
Europe (Text-fig. 2) are based mostly on foraminifera and palynomorphs, (Mamet, 1979; Utting,
1980; Giles, 1981).
Ostracodes from three transgressive marine units of the Windsor Group form the basis of this
study. The oldest ostracodes were collected from a biostromal limestone that occurs within the
Gays River Formation in the Antigonish Sub-Basin. Ostracodes from the Phillips and Dimock
Limestones were collected from the basal member of carbonate-siltstone-evaporitetriplets that
occur in the MacDonald Road Formation of the Minas Sub-Basin. The youngest ostracodes
studied were collected from the Kennetcook Limestone in the Green Oaks Formation of the Minas
Sub-Basin (Text-fig. 2).
I U.S. I
Giles et 01. 1979
Macumber and Gay8
D, P : Dirnock ond Phillips Limestones
K : Kennetcook Limestone
24tratigraphical correlation chart for the Windsor Group.
Klrkbya n. rp. A
Amphirrltor rp. aft.
Balrdla rp. L
Sulcella n. up. A.
Paraparchlter rp. aft.
Polycope n. rp. A.
TEXT-HG.3-Chart showing assemblage distribution of ostracodes from the Windsor Group.
The ostracode assemblages described herein form part of the first ecological study of Mississip
pian ostracodes from the Maritime Basin of Canada. The Nova Scotia assemblages can be related
to similar assemblages described form Newfoundland (Dewey, 1983).
The three Nova Scotia assemblages all represent various types of marine conditions and show
the effects that environmental stress can exert upon the ostracode fauna.
Ostracode assemblage A is based upon material collected from a massive buff-coloured, micritic
limestone in Calpo Quarry, Antigonish. The limestone developed as a bioclastic association over a
granodioritic pluton, blocks of which may be isolated, or form conglomeratic units within the
limestone. A varied mega-fauna of brachiopods, bryozoans, conularids, bivalves and gastropods is
found in the limestone, but corals and crinoids are notably absent. The environment of deposition
is interpreted as a subtidal, drowned topographic high that occurred during the first marine transgression of Windsor times (Geldsetzer, et al., 1980). Nine species of ostracodes were isolated from
the limestone, (Text-fig. 3) and their relative proportions (Text-fig. 4) indicates a paraparchitacean
dominated fauna. Almost 75 % of the fauna is composed of the paraparchitaceans Chamishaella
suborbiculata (Munster) and Shishaella moreyi Sohn. Bairdia sp. L. Sohn forms only about 10%
&Relative percentage diagrams for Nova Scotia ostracode assemblages.
Lower Carbonifeous Ostracodesfrom Nova Scotia 689
of the fauna and the only palaeocope present is Amphissites sp. aff. A . centronotus (Ulrich and Bas&r), individuals of which represent 3 % of the fauna. None of the other components are significant
aoological markers in this assemblage. Ostracode assemblage A is contemporaneous with Newfoundland Assemblage I (Dewey, 1983) and represents a similar. though less diverse fauna. The
osttacode association may suggest a nearshore environment; however, the lack of forams, and
corals or crinoids in the mega-fauna, together with the overlying evaporites that occur throughout the area, also militate in favour of an abnormally saline environment.
Ostracode assemblage B is described from the Dimock and Phillips Limestone units in Wentworth Quarry. The limestones are dark brownlgrey micrites that contain ostracodes, rare brachiopods and the ?bryozoan Palaeocrisidia. Both the Dimock and Phillips Limestones are overlain by
siltstone and thick gypsum/anhydrite units. The repetitive nature of the carbonate-siltstonecvaporite triplets implies a series of transgressive-regressivecycles. The evaporites are considered
to be of supratidal sabkha origin and the limestones are thought to represent a marginal marine
environment (Geldsetzer, et al., 1980). The limestones yield an ostracode fauna of only five species
(Text-fig. 3). More than 75 % of the fauna is composed of Paraparchites sp. aff. P. kellettae Sohn
and Chamishaella suborbiculata (Text-fig. 4); however, there are no spinose paraparchitaceans
present. The sedimentological evidence associated with this occurrence supports the idea that
high abundances of paraparchitaceans in a fauna may be related to a salinity-stressed environment
.-.. . .
5-Growth chart for Parupurchites sp. atT. P. kellettae from Assemblage B, Nova Scotia. (Measurements
are Tn microns).
690 C.P. DEWEY
(Sohn, 1971; Robinson, 1978; Dewey, 1983). An additional 20% of the fauna is composed of
Beyrichiposis lophota Copeland, which is closely allied to the European species B. plicata Jones
and Kirkby. Beyrichiopsis is thought to be an indicator of marginal environments (Becker, et al.,
1974). Growth curves of Paraparchites sp. aff. P. kellettae and Beyrichiopsis lophota (Text-figs. 5
and 6) indicate that the assemblage is an in-situ multigeneration fauna. Acratia acuta (Jones and
. . .'
c - I
. ... . .
...... . .
&Growth chart for Beyrichiopsis lophotu from Assemblage B, Nova Scotia (Measurements are in
Kirkby), a normally wide ranging species is only present as a few individuals, which may suggest
that it is near the end of its ecological tolerance in this environment.
The low diversity and high abundance ostracode fauna is typical of a low level community and
the very large numbers of individuals may reflect a lack of inter-specific competition, rather than a
rich nutrient supply (Levinton, 1970). The assemblage is therefore interpreted as occurring in a
nearshore hypersaline carbonate environment where less tolerant species were unable to survive,
whereas the opportunistic eurytopic species would be abe to thrive in abundance.
Ostracode Assemblage C was derived from the Kennetcook Limestone at the Herbert River
campsite. The massively bedded buff-coloured bioclastic limestone contains a rich fauna of brachiopods, gastropods, bivalves, bryozoans, corals, tentaculitids and crinoid ossicles as well as forams
and twelve species of ostracodes (Text-fig. 3). The environment of deposition is considered to be a
low energy, shallow subtidal environment of near normal marine salinity (Moore, 1967). The ostracodes present in the Kennetcook Limestone constitute the most diverse fauna of the present study,
although the diversity is not as great as that of Newfoundland Assemblage I (Dewey, 1983).
Lower Carboniferous Ostracodesfrom Nova Scotia 691
The most important components of this assemblage are members of the Subfamily Bairdiinae,
which, represented by Bairdia brevis Jones and Kirkby, Bairdia sp. L. and Bairdiacypris guartziuna
Egorov, constitute 42% of the fauna, (Text-fig. 4). Studies of both Recent and Carboniferous
species of Buirdia (Kornicker, 1961 ; Kaesler, 1982) indicate that greatest abundances of the genus
o m r in stable shallow subtidal offshore environments of normal marine salinity.
The second most important group in Assemblage C is the Palaeocopida which accounts for 37 %
of the fauna. The most common plalaeocope is Kirkbya n. sp. A, although rare individuals of
‘%ortanella7’ sp. and Beyrichiopsis cornuta Jones and Kirkby are also present. Carboniferous
palaeocopes are thought to be more abundant in nearshore environments, being commonly replaced in the offshore by podocopids, although kirkbyacean palaeocopes may also become important (van Ameron, et al.. 1970; Becker, et al., 1974; Kaesler, et al., 1977; Kaesler, 1982). This would
account for the rarity of non-kirkbyacean palaeocopes in Assemblage C.
It is significant that the single paraparchitacean species present in Assemblage C, Chamishaella
.... .... .
1000 1200 1400 1800
... .. . ...
7-Growth charts for a) Kirkbya n. sp. and b) Bairdia sp. L. from Assemblage C, Nova Scotia(MeasWe*merits are in microns).
Lower CarboniferousOstracodes from Nova Scotia 693
suborbiculata accounts for only 5 % of the total preserved population. It is probable that paraphitaceans, which were more adaptable to unstable nearshore conditions, were replaced by
bairdiaceans (which are less tolerant of environmental stress) in the more stable environments further from shore (Ferguson, 1962, 1974).
Other minor elements of the fauna include a few individuals of Monoceratina youngiana (Jones
and Kirbky). The genus Monoceratina is often a rare component of ostracode faunas (Roth, 1928;
Sohn, 1977) and is frequently associated with fine sediments in shallow marine environments (Donze, 1971; Swain and Kraft, 1975; Sokac, 1977). Also present are several specimens of Polycope
n. sp. A which by analogy to modern species (Sars, 1928; Elofson, 1941; Joy, 1974) are interpreted
as swimming or burrowing benthic ostracodes. A less significant member of the assemblage is bairdiocypridid gen. et sp. indet. which supports the idea that bairdiocypridids often co-occur with
Bairdia (Becker, et al., 1974). Acratia acutu is also present, but is a wide ranging species of little
When examined as a whole, the ostracode associations of this assemblage indicate that the environment of deposition may have been in a shallow subtidal offshore area. The assemblage shows a
high carapace to valve ratio, which, combined with the instar series in Bairdia sp. L and kirkbya
n. sp. A (Text-fig. 7) suggests a lack of post-mortem transport. The assemblage does not show a very
high species diversity; however, the presence of corals, crinoids and foraminifers would suggest
that salinity was not a controlling factor. It is more likely that there were fewer niches available
for colonisation in this assemblage than in the biohermal Assemblage I from Newfoundalnd
Ostracode assemblages described from the three marine transgressive environments in Nova
Scotia (Plates 1 and 2) show many faunal characteristics that are similar to those described from
Newfoundland (Dewey, 1983). Most ostracode assemblages from both Newfoundland and Nova
Scotia are indicative of fairly unstable, nearshore marine conditions. Sedimentological and faunal
evidence also supports the notion that the transgressive cycles that produced these conditions were
often associated with hypersalinity. The sum of these ecological controls led to the development of
predominantly paraparchitacean dominated ostracode faunas in a variety of different nearshore
environments (viz: Assemblages I to V in Newfoundland (Dewey, 1983) and Assemblages A and B
in Nova Scotia). The only exception to this is Assemblage C in Nova Scotia. In Assemblage C the
mega-faunal evidence indicates that salinity was not a major control in the environment, and the
ostracode fauna suggests that the environment was sufficiently stable and far enough from shore
to allow the devleopment of a Bairdia rich fauna.
I would like to express my gratitude to my Ph. D. supervisor, Lars Fahraeus, for guiding me
l-Fig. 1. “Gortanella” sp., right aspect, ~ 6 2 Fig.
2. “Gortamlla” sp., left aspect, X75. Fig. 3. Kirkbya
n. sp. A, left aspect, x 60. Fig. 4. Amphissites sp. aff. A. centronotur. right aspect, x 82. Fig. 5. Bairdia brevis,
right aspect, ~ 6 8 Fig.
6. Bairdasp. L, right aspect, x44. Fig. 7. Bairdaoypris quartziann, right aspect, X45.
Fig. 8. Acratia acuta, left aspect, x62. Fig. 9. Sulcella n. sp. A, left aspect, ~ 6 0 Fig.
. 10. Sulcella n. sp. A,
dorsal aspect, x 60.
Lower Carboniferous Ostracodes from Nova Scoria 695
through the doctoral program. I would also like to thank Ernie Russell for reviewing earlier verSions of the manuscript; and Elisabeth Dewey for her drafting abilities.
This study was funded by a Memorial University Doctoral Fellowship to the author, and a
Natural Sciences and Engineering Research Council of Canada grant to my supervisor. Incidental
costs of publication were met by the Department of Geology and Geography at Mississippi
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2-Fig. 1. Paraparchites sp. aff. P. kellettae, right aspect, x 25. Fig. 2. Chamishaella suborbiculata, right
aspect, X 40. Fig. 3. Shishaella moreyi, right aspect, x 80. Fig. 4. Healdimlla sp., right aspect, X 70. Fig.
5. Polycope n. sp. A, right aspect, x 300, Fig. 6. Beyrichiopsis cormta, left, aspect, x 70. Fig. 7. Beyrichitpsis
lophota, left aspect, x 60. Fig. 8. Monoceratina youngiana, right aspect, X 115. Fig. 9. Bythocypris aequafk
right aspect, ~ 5 5 .
696 C.P. DEWEY
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