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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 39 (1989), Pages 375-383

Stratigraphic Relationships Between Odontogryphaea Thirsae Beds and the Big Shale of the Wilcox (Paleocene-Eocene) in Louisiana

Lloyd N. Glawe (1)

ABSTRACT

The relationship between beds of the oyster Odontogryphaea thirsae of the surface Wilcox Group exposures in the Sabine Uplift area of northwestern Louisiana and the Big Shale, a well-known subsurface mapping unit in central Louisiana, has been unclear. In a paleontological study of 2158 feet of continuously cored Wilcox from Sabine Parish, planktic foraminiferal biostratigraphic zones were determined that include: Globorotalia angulata and G. pusilla pusilla (P3), G. pseudomenardii (P4), and G. velascoensis (P5). The Odontogryphaea thirsae bed was assigned to the Globorotalia pseudomenardii zone.

Electrical-log sections were used to demonstrate (1) the correlation between the Odontogryphaea thirsae bed in the corehole and the O. thirsae bed exposed at the surface at Many, Louisiana, a distance of six miles, and (2) the correlation between the base of the 10 ft thick shale beneath the O. thirsae bed in the corehole and the base of the Big Shale as recognized in the central Louisiana subsurface.

Based on its assigned biostratigraphic zone, the O. thirsae bed in the updip Wilcox corehole is equivalent, in part, to the Big Shale of the basinal Wilcox of east-central Louisiana, which has previously been included in the Globorotalia pseudomenardii zone. Paleontologic recognition of a thin marine unit one foot above the Odontogryphaea thirsae bed in the corehole on the southern flank of the Sabine Uplift provides documentation of the transgressive character of the Big Shale/O. thirsae sequence and is evidence of the existence of the TP 2.1 cycle in Louisiana.


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