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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 31 (1981), Pages 283-287

Macrofossil Assemblages of the Moodys Branch Formation (Upper Eocene), Louisiana and Mississippi

Susan R. Elder, Thor A. Hansen (1)


The Moodys Branch Formation (Upper Eocene, Jackson Group) is a thin, fossiliferous, glauconitic sand which represents the destructive shelf phase of a transgressive sea. Computer cluster analysis of fossils taken from closely spaced samples reveals six distinct macrofossil assemblages: A) open bay, B) nearshore, C) inner shelf, D) western inner middle shelf, E) eastern inner middle shelf and F) outer middle shelf. Quantitative trends are similar to Holocene trends for dead shell assemblages in that species dominance and numbers of individuals increase nearshore and diversity, as measured by the Shannon-Weiner index, increases offshore and in bays. However, there are conspicuous differences in the environmental preferences of some Eocene species and their closest living analogs. This suggests that care should be taken when making ecological analogies between modern organisms and fossil remains.

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