Cephalopod Diversity within a Concretionary Inverval of the Pierre Shale (Upper Cretaceous) in Dawes County, Northwestern Nebraska

Authors

Darryl Tharalson, Chadron State College

Date of this Version

1993

Comments

1993. Transactions of the Nebraska Academy of Sciences, XX: 87-95. Copyright © 1993 Tharalson.

Abstract

A concretionary interval within the Pierre Shale, where it outcrops across northern Dawes County, is characterized by a diversity of cephalopod taxa. The interval falls within the ammonite zones of Exiteloceras jenneyi to Baculites cuneatus of the upper Campanian. Three or more of the following cephalopod taxa have been collected at each of the seventeen sites described herein: Eutrephoceras dekayi (Morton); Baculites compressus Say; B. cuneatus Cobban; Didymoceras cheyennense (Meek and Hayden); Exiteloceras jenneyi (Whitfield); Jeletzkyites nodosus (Owen); Placenticeras intercalare Meek; P. meeki Boehm; and Solenoceras cf. S. crassum (Whitfield). The interval that yields cephalopod diversity comprises a stratigraphic thickness of about 15 to 20 meters and appears to occur roughly 300 meters above the base of the Pierre Shale in northeastern Dawes County. The fossils are present within calcareous concretions imbedded in gray to olive-gray shale in the lower portion of the upper part of the Pierre Shale in this area. The interval seemingly correlates, at least in part, with the lower unnamed shale member of the Pierre Shale in the Red Bird area in eastern Wyoming.