PALYNOMORPHS OF THE CLAYTON FORMATION, SOUTHEASTERN MISSOURI, AS INDICATORS OF TIME AND DEPOSITION THROUGH THE K/PG MASS EXTINCTION EVENT

Sedimentary deposits in the southeast region of Missouri’s boot-heel near the town of Bloomfield, reveal a biostratigraphic record across the K/Pg boundary. The K/Pg transition sequence is represented by the late Maastrichtian Owl Creek Formation and the Paleocene Clayton and Porters Creek Formations. The Clayton Formation is characterized by a basal fossiliferous coquinite that contains the late Maastrichtian index ammonites Discoscaphites iris and Eubaculites carinatus, as well as rip-up clasts containing tektite-like spherules which may be direct evidence of a bolide impact. We use dinoflagellate occurrences in these units to determine the timing of the coquinite layer and specifically whether or not it is the result of an impact-generated tsunami associated with the end-Cretaceous impact. Fourteen sediment samples were collected from the study site at 25 cm intervals from the upper Owl Creek Fm to the base of the Porters Creek Fm. Preliminary palynological results indicate the presence within the Clayton basal coquinite of two dinoflagellates considered to be indicators of the uppermost part of the upper Maastrichtian (Palynodinium grallator and Disphaerogena carposphaeropsis) and two middle late Maastrichtian forms (Deflandrea galeata and Thalassiphora pelagica). All of these taxa are found within the uppermost Owl Creek and the lowermost section of the coquinite of the lower Clayton. The middle horizons of the coquinite preserve sparse dinoflagellate occurrences representing only stratigraphically and temporally wide-ranging taxa. The uppermost coquinite has a higher dinoflagellate recovery, similar to the basal section, and contains the uppermost Maastrichtian index forms, Palynodinium grallator and Deflandrea galeata. So far no Danian dinoflagellates have been recovered from the coquinite. The dinoflagellate data support the ammonite record in indicating a latest Maastrichtian age for the basal Clayton coquinite, and suggest that the spherule-bearing rip-ups may represent deposition from an impact-induced tsunami.