Date of Award

1970

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

F.D. Holland, Jr

Abstract

The Pierre Shale of Campanian and Early Maestrichtian age in Bowman County, southwestern North Dakota, has an abundant molluscan fauna and 51 species are described herein. The 51 species consist of 1 species of scaphopod, 13 species in 11 genera of gastropods, 24 species' in 17 genera of bivalves, and 13 species in 6 genera of cephalopods.

The stratigraphy of the Pierre Shale in Bowman County was not compiled into a composite section because of the homogeneity of the shale, the lack of distinctive lithologic units, and the slumped condition of the shale. However, the biostratigraphic position of the Bowman County portion of the Pierre was determined by the use of the baculites. The Baculites reesidei and questionably, the B. grandis B.ange Zones were recognized; but the intervening range zones, B. baculus, B. jenseni, and which occur in other areas between, the B. reesidei and B. grandis Zones were not found in Bowman County.

The compositions of the shale and concretions from the Pierre Shale in the area studied were determined by X-ray diffraction and by dissolving the samples in dilute HCl. The shale has a composition that remains constant throughout the area. The composition of the concretions is slightly variable. The main constituents of the concretions and shale are clay minerals, quartz, and calcite. There are minor traces (less than 2 per cent) of gypsum, potassium feldspar, plagioclase, and pyrite in both the shale and concretions.

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