Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Gerry Clarkson
Dr. W. Thomas Straw
Dr. William Harrison III
Masters Thesis-Open Access
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.
Suh, "A Seismic Study of an Impact Feature in Cass County, Michigan" (1985). Master's Theses. 1444.