Date of Award

4-2019

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. Alan E. Kehew

Second Advisor

Dr. William A. Sauck

Third Advisor

Dr. Robb Gillespie

Keywords

geophysics, bedrock topography, glacial, HVSR, passive seismic

Access Setting

Masters Thesis-Open Access

Abstract

Geophysical methods were used to estimate bedrock depths below sedimentary cover and infer previously unknown features in two adjacent topographic quadrangles (Climax & East Leroy) in Michigan, USA. The study area contains mostly Mississippian Shale bedrock overlain by Wisconsin-aged glacial drift deposited during multiple glacial advances and retreats of the Saginaw Lobe (Laurentide Ice Sheet). These glacial events created complex landform assemblages that have only recently been mapped in detail near-surface, but are still poorly understood in the subsurface. Buried bedrock valleys typically contain coarse glacial sediment and thus are valuable aquifers, but these can be difficult to locate due to a lack of surface expression and bedrock topography information. The Horizontal to Vertical Spectral Ratio (HVSR) technique was used to estimate the thickness of the upper of a two-layer case where a soft unconsolidated geologic layer (glacial sediment) is underlain by a harder substrate (bedrock). Additional techniques such as vertical resistivity soundings and active seismic refraction/reflection surveys were employed to compare with HVSR, boring logs, and industry seismic data results to better understand the subsurface. This study resulted in the discovery of several bedrock lows that are interpreted as bedrock valleys or tunnel valleys, which may contain aquifers and provide insight to Pleistocene glacial history. Bedrock highs correspond to terminal ice margins and have some control over post-glacial drainage systems.

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