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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 39 (1989), Pages 365-374

Paleoecology of the Eocene Wheelock Member of the Cook Mountain Formation, in Western Houston County Texas

Barbara A. Gaskell (1)

ABSTRACT

Eighty-five species of foraminifera and forty-nine molluscan species were recovered from the Wheelock Member of the Cook Mountain Formation, in the Porter Springs area of Houston County, Texas and along the Little Brazos River in Brazos County, Texas.

The Wheelock Member is primarily a regressive unit. A thin shell lag deposit at the base of the member is all that remains of the transgressive part of the sequence.

Above the shell lag deposit, the lower part of the member consists dominantly of bioturbated, glauconitic, fossiliferous mudstone. The percentage of planktic foraminifers and the diversity of benthic foraminifers suggests deposition in an inner or inner-middle shelf environment. The low diversity and equitability of the molluscan population and the abundance of opportunistic corbulid bivalves suggest that the environment was at least periodically unstable.

The upper part of the Wheelock Member consists dominantly of regularly layered or laminated mudstone and siltstone and contains only a low diversity assemblage of agglutinated foraminifera. This part of the member was probably deposited in a shallow, brackish water environment with a high sedimentation rate.

Planktic foraminifers recovered from the Wheelock member support an age correlation with the late Middle Eocene Morozovella lehneri or Orbulinoides beckmanni Zones. According to Berggren and others (1985), this corresponds to an absolute age of between 42 and 46 million years B.P.


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