Earth and Atmospheric Sciences, Department of
Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research
First Advisor
M. Dane Picard
Date of this Version
2-1968
Document Type
Thesis
Citation
A thesis presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of the requirements for the degree of Master of Science
Department of Geology
Under the supervision of Dr. M. Dane Picard
February 1968, Lincoln, Nebraska
Abstract
The Chugwater Group (Triassic), on the east side of the Bighorn Mountains of Wyoming and Montana, forms a narrow outcrop band of hogbacks. Four redbed formations are included in the Chugwater. From base to top they are: 1) Red Peak, 2) Crow Mountain, 3) Jelm, and 4) Popo Agie. The Chugwater is disconformably underlain by t];ie Goose Egg Formation (Permian) and unconformably overlain, from south to north, by the Sundance, Gypsum Spring, and Piper Formations of Jurassic Age.
The rocks of the Chugwater, in order of abundance, are: siltstone, sandstone, claystone, conglomerate, limestone, dolomite, and gypsum. Binocular microscope studies were made to determine lithologic characteristics. This analysis included color, roundness, sorting and cement.
Splitting properties, bedding and sedimentary structures were recorded in the field. The Red Peak is predominantly platy to slabby, with the exception of massive intervals in the alternating facies. The Crow Mountain is dominantly massive and the Jelm and Popo Agie are dominantly slabby. Horizontal and wavy bedding, and cross-stratification are the most abundant bedding types. Ripple-stratification, graded bedding, disturbed bedding, and convolute bedding occur in lesser amounts.. Percentages of bedding types were determined. Paleocurrent directions were determined from ripple marks, cross-stratification, parting lineation, and flute casts. The principle paleocurrent directions during Red Peak deposition were northwest, and during Crow Mountain deposition, southwest.
Advisor: M. Dane Picard
Comments
Copyright 1968, Robert C. McLellan. Used by permission