MIOSPORE BIOSTRATIGRAPHY AND IDENTIFICATION OF THE KINDERHOOKIAN-OSAGEAN BOUNDARY IN THE MICHIGAN BASIN

Since its original description by Houghton (1841), the Michigan Basin has been a focal point for stratigraphic and biostratigraphic studies. The lack of significant outcrops within the basin has made the studies difficult, especially from a biostratigraphic viewpoint. The ‘bulls-eye’ structure of the basin, which covers approximately 207, 000 km2, contains rocks that range from the Precambrian to the Jurrassic. The current study focuses on part of the Lower Mississippian clastics within the basin, specifically the relationship between the Coldwater Shale and Marshall Sandstone succession and the Kinderhookian-Osagean boundary. Previous biostratigraphic studies on these two units have yielded a wide-range of results (Monnet, 1948; Cohee et al., 1951; Miller and Gardner, 1955; and Driscoll, 1965). See (1980) sampled and prepared miospore assemblages from three locations on the southern peninsula of Michigan. The three locations yielded 15 samples, including five from the Coldwater Shale and ten from the Marshall Sandstone. The miospore assemblages from this succession were of moderate abundance and moderate diversity. The Coldwater Shale miospore assemblage is dominated by Punctatisporites solidus, P. minitus, and specimens of Vallatisporites. Biostratigraphically important taxa in the Coldwater Shale include Spelaeotriletes balteatus and S. crustatus. The overlying Marshall Sandstone also yielded an assemblage dominated by Punctatisporites solidus, P. minitus, and specimens of Vallatisporites; however, several new species occur in the Marshall Sandstone, including the zone-defining Spelaeotriletes pretiosus. Based on the miospores, the author has determined with confidence the Coldwater Shale-Marshall Sandstone boundary is coeval with the Kinderhookian-Osagean boundary within the Michigan Basin, is representative of the miospore biozones in western Europe, and can be correlated to other locations worldwide.