--> ABSTRACT: Paleoenvironments of Upper Cretaceous Lewis Shale and Fox Hills Formation, South-Central Wyoming, by Roseanne C. Perman; #91030 (2010)

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Paleoenvironments of Upper Cretaceous Lewis Shale and Fox Hills Formation, South-Central Wyoming

Roseanne C. Perman

The Maestrichtian Lewis Shale and Fox Hills Formation in south-central Wyoming were deposited during the final major transgression and regression of the North American epicontinental sea. Outcrops of these formations were examined along the margins of the Great Divide, Washakie, Hanna, and Carbon basins. Bore-hole logs from approximately 200 wells within these basins were studied and correlated with outcrops. Lists of fossils from nearly 300 localities were compiled to obtain information on paleoenvironments and to identify stratigraphic positions of fossils indicating ages of the formations. The Lewis Shale is divided into lower and upper, predominantly shale members and the intervening Dad Sandstone Member. The lower shale member contains mostly deep-water marine facies, except in t e Hanna basin where it contains sandstone units representing barrier bar facies. The Dad Sandstone was deposited in deep-water to marginal marine environments. Sandstone and interbedded shale units include prodelta turbidite facies, storm-deposited delta front facies, and barrier bar/lagoon facies. The upper shale member represents relatively shallow-water shoreface and delta front facies. The Fox Hills Formation contains sandstone and shale units that represent shallow-water shelf through delta plain facies. The Lewis Shale and the Fox Hills Formation are older in the northern part of the region and progressively younger to the south. Northern marginal marine and shallow-water shelf facies correlate with southern deep-water facies. Distribution of facies and ages of units indicate delta progradation to the south. The source area for the two formations was the Sheridan delta.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.