Date of Award

8-1985

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. Gerry Clarkson

Second Advisor

Dr. W. Thomas Straw

Third Advisor

Dr. William Harrison III

Access Setting

Masters Thesis-Open Access

Abstract

A geophysical investigation, including a seismic study, of the subsurface structure of the Calvin-28 oil field, Cass County, Michigan, indicates that the structure's origin may be related to an impact event. The structural closures in the time structure maps and drilling results both show a central uplift. The fault system in the Trempealeau Formation shows a structure similar to other proven astroblemes. Undisturbed layers just beneath the central uplift also provide evidence of an impact structure. The result of mathematical modeling of the central uplift under the assumption that the structure is an impact structure corresponds well with the drilling results. Therefore it may reasonable to accept the impact origin for the Cass County structure.

The impact event occurred on the Utica shale of the Late Ordovician age. The diameter of the original crater was at least 2 kilometers. The mass of the meteorite was about 9 x 104 tons.

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