Publication Date


Document Type


First Advisor

Stoddard, Paul

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology


Geology--South Dakota--Fall River County; Sandstone--South Dakota--Fall River County


The sandstone structures that occur within the Skull Creek and Mowry shale units in Fall River County, South Dakota, and throughout the southern Black Hills uplift have been the subject of very few studies. The origin of the sediments and the nature of the forces that caused the structures to form has been disputed since Darton first discovered them in 1901. The sediments have been determined to have been derived from a discontinuous sandstone bed that occurs within the Mowry shale. The morphology of the lenses and dikes indicates that they are the result of the fluidization of the discontinuous sandstone bed. This fluidization occurred as the result of either overpressuring of the sediments from the compaction of the surrounding shale, or cyclic loading due to seismic shaking. It has not yet been determined which of these processes caused the liquefication, or if the liquefication was the result of a combination of both processes. The lenses and dikes have also been subjected to secondary structural and mineralogic alteration. The orientation of the dikes and the joints within the lenses can be related to the regional fracture systems, and have been inferred to have occurred contemporaneously with the formation of the regional joint system, after the emplacement and lithification of the lenses and dikes. Also, the replacement of the cementing agents in the sediments by iron oxide has been observed. These observations and conclusions have provided a new, and very different, explanation of the sandstone lenses and dikes that occur within the study area and throughout the southern Black Hills uplift.


Includes bibliographical references (pages [86]-88)


xi, 133 pages




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