Molluscan record from a Mid-Cretaceous borehole in Weston County, Wyoming

Abstract

A core borehole in the Osage oilfield on the west flank of the Black Hills uplift in eastern Wyoming penetrated, in decending order, most of the Carlile Shale, all of the Greenhorn Formation, and the upper part of the underlying Belle Fourche Shale. Molluscan fossils are abundant in parts of the core and indicate an age span of early Coniacian to the middle Cenomanian. Most of the fossils are bivalves and ammonites; gastropods are scarce. Fossils in the cores indicate the following zones: Lower Coniacian Cremnoceramus? waltersdorfensis Upper Turonian Scaphites coroensis S. nigricollensis S. whiifieldi S. warreni Middle Turonian Collignoniceras woollgari Lower Turonian Mytiloides mytiloides Mytiloides aff. M. duplicostatus Upper Cenomanian Sciponoceras gracile Dunveganoceras albertense D. pondi Middle Cenomanian Acanthoceras amphibolum