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Chapter 49. Lower Carboniferous ostracode assemblages from Nova Scotia

Chapter 49. Lower Carboniferous ostracode assemblages from Nova Scotia

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686 C.P.DEWEY

m



C I Cumberland

MI Minas

A: Antigonish

Ma 1 Mabou



s



2



0



:Land areas



Sub- Basins



Sydney



TEXT-FIG.

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).



687



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CANADA



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5



Faunal

Subronw

Bell

1927, 1929



NOVA SCOTIA

Giles et 01. 1979

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D, P : Dirnock ond Phillips Limestones



K : Kennetcook Limestone

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TEXT-FIG.

24tratigraphical correlation chart for the Windsor Group.



"Gortanellal' ep.

Klrkbya n. rp. A

Amphirrltor rp. aft.

A. contronotur

Balrdla brevlr

Balrdla rp. L

Balrdlacyprir quartziana

Acratla acuta

Bythacyprir oequalir

Monoceratina youngiana

Beyrlchloprlr cornuto

Boyrichiopsir lophota

Sulcella n. up. A.

Healdlanella UP.

Paraparchlter rp. aft.

P. kellettae

Chamlrharlla ruborbiculata

Shirharlla moreyl

Polycope n. rp. A.



*



TEXT-HG.3-Chart showing assemblage distribution of ostracodes from the Windsor Group.



688 C.P.DEWEY



OSTRACODE

ASSEMBLAGES

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%



ASSEMBLAGE A



ASSEMBLAGE B



I!



PARAPARCHITACEA

BAlRDllNAE

PALAEOCOPIDA



BEYRICHlOPSlS



OTHER



TEXT-FIG.

&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



1



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TEXT-FIG.

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



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TEXT-FIG.

&Growth chart for Beyrichiopsis lophotu from Assemblage B, Nova Scotia (Measurements are in

microns).



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



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TEXT-FIG.

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

ecological significance.

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

(Dewey, 1983).



CONCLUSIONS

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.



ACKNOWLEDGEMENTS

I would like to express my gratitude to my Ph. D. supervisor, Lars Fahraeus, for guiding me

RATE

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

State Universisty.



REFERENCES

and COTE, P.R. 1964. Lower Carboniferoussedimentary rocks in southwesternNewfoundland and their

relations to similar strata in western Cape Breton Island. Can. Min. and Met. Bull., 57, 507-520.

BECKEX, G., BLESS, M.J.M., STREEL,M.and THOREZ,J. 1974. Palynology and ostracode distribution in the upper Devonian

and basal Dinantian of Belgium and their dependence on sedimentary facies. Mededelingen Rijks. Geol. Dienst.

Neiuwe Serie, 25 (2), 99 pp.

BELL, W.A. 1927. Outline of Carboniferousstratigraphy and geologic history of the Maritime Provinces of Canda.

Trans. Roy. SOC.Can., Ser. 3, 2, 75-108.

- 1929. Horton-Windsor district, Nova Scotia. Geol. Surv. Can., Mem. 155, 268 pp.

DEWEY,C.P. 1983. Ostracode palaeoecology of the lower Carboniferous of western Newfoundland. In MADDOCKS,

R.F. (ed.). Applications of Ostracoda, 104-1 15. Department of Geosciences, Univ. Houston, Texas.

DONZE, P. 1971. Rapports entre les facies et la repartition generique des ostracodes dans quatre Gisement-types,

a dew synchroniques, du Berriasien du sud-est de La France Bull. Centre de Rech. Pau. S.N.P.A., 5, suppl., 651662.

BLOFSEN, 0.1941. Zup Kenntnis der Marinen Ostracoden Schwedens mit besonderer Berucksichtigungdes Skageraks.

2001.Bidrag, Uppsala, 19, 286 pp.

FEROUSON, L. 1962. The palaeoecology of a lower Carboniferous marine transgression. J. Paleont. 36, 1090-1107.

- 1974. The palaeoecological and taxonomic significance of growth series of the ostracode genera Bairdia and

Paraparchites from a Scottish lower Carboniferous shaIe. Geol. SOC.Amer. Abst. with Programs, 1974, 732.

QIXDSETZER, H., GILES, P., MOORE, R. and PALMER, w. 1980. Trip 22: Stratigraphy, sedimentology,and mineralisation

of the Carboniferous Windsor Group, Nova Scotia. 42 pp. Halifax ‘80 GACIMAC Field Trip Guidebook.

GILES, P. 1981. Major transgressive-regressive cycle in middle to late Visean rocks of Nova Scotia. Nova Scoria Dept.

of Mines and Energy, Paper 81-2, 27 pp.

- BOEHNER, R.C. and RYAN, R.J. 1979. Carbonate banks of the Gays River Formation in central Nova Scotia.

Nova Scotia Dept. of Mines and Energy, Paper 79-7, 57 pp.

JOY, J.A. 1974. The distributionandecology of the benthic ostracodafrom the central Arctic Ocean. 116pp. Unpublished

M. Sc. thesis, Univ. Wisconsin.

KAESLER, R.L. 1982. Ostracoda as envrionmental indicators in late Pennsylvanian subsurface shales. Third North

Amer. Conv. Proc.. 1, 275-280.

- PETERSON, R.M. and BRONDOS, M.D. 1977. Environmental control of patterns of hierarchical diversity among

late Palaeozoic Ostracoda. Geol. SOC.Amer. Abst. with Programs, 1977, 1042.

KNIGHT, I. 1983. Geology of Carboniferous Bay St. George sub-basin western Newfoundland. Min. Dev. Div., Nfld.

Dept. Mines and Energy, Mem. 1, 358 pp.

KORNICKER, L.S. 1961. Ecology and taxonomy of Recent Bairdiinae (Ostracoda). Micropalaeontology, 7, 55-70.

- 1964. Ecology of Ostracoda in the northwestern part of the Great Bahama Bank. Publ. Staz. 2001.Napoli, 33

SUPPI., 345-360.

LEVINTON, J.S. 1970. The palaeoecological significance of opportunistic species. Lethaia. 3, 69-78.

MAMET, B.L. 1970. Carbonate microfacies of the Windsor Group (Carboniferous), Nova Scotia and New Brunswick.

Geol. Surv. Can. Pap. 70-71, 121 pp.

MOORE, R.G. 1967. Lithostratigraphicunits in the upper part of the Windsor Group, Minas sub-basin, Nova b t i a .

In Neale, E.R.W. and Williams, H. (eds.). Geol. Assoc. Can. Sp. Pap. (4), 245-266.

ROBINSON, E. 1978. The Carboniferous. In Geological Journal Special Issue (8), 121-166, See1House Press, Liverpool.

ROTH, R. 1928. Monoceratina, a new genus of Ostracoda from the Pennsylvanian of Oklahoma. J. Paleont.. 2,15-19.

SARS, 0.0. 1928. An account of the Crustacea of Norway, D[,Ostracoda. 277 pp., PIS. 1-19, Bergen.

&URD, D.M.



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 .



PLATE



696 C.P. DEWEY

SOHN, 1.0.1971.New



late Mississippian ostracode genera and species from northern Alaska. U.S.G.S. prof. Pap.

711-A,24 pp.

- 1977. Late Mississippian and early Pennsylvanian Ostracoda from northern Arkansas-a preliminary survey.

Oklahoma Geol. Surv. Guide Book 18, 149-159.

SOKAC, A. 1977.Ostracoda from bottom cores off the coast of Montenegro, I n LOEFFLER, H. and DANIELOPOL, D. (eds.).

Aspects of ecology and zoogeography of Recent and fossil Ostracoda, 223-234 W. Junk, The Hague.

SWAIN, F.M. and KRAIT, J.C. 1975.Biofaciesand microstructure of Holocene Ostracoda from tidal bays of Delaware.

Bull. Amer. Pal., 65, 601-622.

UITING, J. 1980.Palynology of the Windsor Group (Mississippian)in a borehole at Stewiacke, Shubenacadie&Sin,

Nova Scotia. Can. J. Earth Sci., 17(8), 1031-1045.

VAN AMERON, H.w.J., BLESS, M.J.M. and WINKLER-PRINS, C.F. 1970.Some palaeontological and stratigraphic aspects

of the upper Carboniferous Sama Formation (Asturias, Spain). Mededelingen Rijks. Geol. Dienst. Nieuwe

Serie, 21,9-79.



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