Master's Theses

Date of Award

1979

Degree Name

Master of Science (MS)

Department

Geosciences

Advisor

Michael E. Nelson

Abstract

The Crow Creek Member of the Pierre Shale (Upper Cretaceous) is a westward projecting tongue of siltstone overlain by marl, which crops out along the Missouri River and its tributaries in South Dakota. / Seventy-nine samples from 15 measured sections and one subsurface core were analyzed for x-ray bulk rock mineralogy, insoluble residues, and limited clay mineralogy, heavy minerals, and paleontologic elements. X-ray diffraction values reveal geographic and stratigraphic trends in the four major mineralogic components (quartz, calcite, dolomite, and clay minerals). These, coupled with trends in the insoluable residue values, suggest that the Crow Creek sediments were deposited in a transgressive, near shore, shallow shelf environment. Elements of the fauna support this and also suggest that the unit was deposited in near normal to normal marine, mid to warm temperate waters. Periodic (probably seasonal) high energy conditions disrupted the bottom community and led to physical destruction of most macrofossil shells. The shell fragments were then subjected to geochemical destruction and/or alteration. Dolomite was formed by both supratidal flat and reflux mechanisms. Regional epeirogenic uplift in east-central and southeastern South Dakota supplied the detrital fraction and, coupled with the transgression, controlled the geographic and lithologic configurations of the member.

Rights

Copyright 1979 Richard F. Bretz

Comments

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