Thermal History of the Michigan Basin from Apatite Fission-Track Analysis and Vitrinite Reflectance

Kinetic models for apatite fission-track annealing and vitrinite maturation were used to examine hypotheses for the burial and thermal history of the Michigan basin. Fission-track ages between 160 and 200 Ma were measured for Carboniferous outcrop samples (>300 Ma) near Saginaw Bay. Published vitrinite reflectance and conodont alteration data from the Michigan basin are higher than predicted from current depths and temperatures for the samples. Both sets of data are broadly consistent with elevated temperatures due to additional burial at present geothermal gradients. The depth of additional burial varies systematically from less than 1 km in the basin center to more than 2 km near the adjacent arches. The additional burial could explain the occurrence of diagenetic banding in portions of the St. Peter Sandstone that are currently at depths shallower than the critical window for this phenomenon.