HIGH RESOLUTION CONODONT BIOSTRATIGRAPHY OF THE DUNDEE LIMESTONE, MICHIGAN BASIN

The relative age of the Dundee Limestone within the Michigan Basin has been widely disputed within the literature, with limited studies constraining the formation to a single biozone. This research extends the geographic sampling range of previous studies and examines subsurface samples collected from the center of the basin. Core samples obtained from the South Buckeye Oil Field in Gladwin County, Michigan were processed and produced a low yield of approximately 4 conodonts per kilogram. Two conodont species were present: Icriodus angustus and Icriodus orri. The fauna found represent a low-diversity, shallow-water, Icriodus-dominated fauna, implying that the center of the structural basin was overlain by a shallow water carbonate ramp during the Middle Devonian. The species found constrain the Dundee Limestone to deposition occurring from the base of the australis zone (389 Ma) to the top of the ensensis zone (388.1 Ma). This conodont biozonation correlates the Dundee Limestone to the Delaware Limestone of the Appalachian Basin and the Speed Member of the North Vernon Limestone in the Illinois Basin. Additional conodont color alteration index methodology concludes that the rocks within sampled section have been exposed to average temperatures ranging between 110^o to 200^oC and show temperature variation indicative of hydrothermal alteration.