Shelley Ann Thibaudeau

Representative taxa from 10 genera of agglutinated foraminifera, and 3 genera of arcellacea are described from the Upper Pennsylvanian (Westphalian D), coal-bearing strata of the Sydney Mines Formation, Cape Breton Island, Nova Scotia. Detailed taxonomic study resulted in the identification of the following foraminiferal genera: Ammobaculites, Ammomarginulina, Ammotium (2 forms), ?Buccicrenata (2 forms), Haplophragmoides, Miliammina, Sorosphaera, ?Textularia, Trochammina (4 forms) and Trochamminita. The following genera represent the arcellacea: Difflugia (3 forms), Heleopora, and ?Paranebela. Specimens of the plychaete worms genus Spirorbis, a branchiopod crustacean ?Limnestheria sp., and a ?nepionic nautiloidean cephalopod are also described.

Agglutinated foraminifera are present in 8, of the 9 separate lithologic units, and this presence provides positive evidence for marine influence in the environments of deposition. Carboniferous microfossil assemblages are compiled, and compared to foraminiferal-arcellacean assemblages that characterise Recent fresh water through transitional-marine and saline environments. A salinity range, and an environment of deposition are interpreted, for each unit, based mainly on the generic diversity of the protistan assemblage. The marine-influenced environments of deposition include: nearshore to abandoned delta lobe, interdistrubutary bay through levee-crevasse splay, lower estuarine to transitional marine, and low to middle marsh. One fresh water, lacustrine or upper estuarine-riverine setting is identified.

The diversity of the representative agglutinated taxa of brackish water foraminiferal-arcellacean assemblages remains stable after more than 300 million years. The co-occurrent finds of agglutinated brackish water foraminifera and other fossil biota infer a tolerance to salinity fluctuations by the other organisms. An euryhaline-marine, rather than fresh water, habitat for these biota is also indicated by this relationship. Protistan assemblages are used to positively differentiate fresh water from marine-influenced coastal deposits, and to delimit cyclic sedimentary sequences that are due to sea-level fluctuations.

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Pages: 155
Supervisor: Franco Medioli and David Scott