Palynomorphs and Paleoenvironmental Significance of the Cretaceous-Tertiary Transition In Southeastern Missouri

The Cretaceous-Tertiary transition in southeastern Missouri represents the northwestern extension of the Mississippi Embayment where the Danian Clayton Formation unconformably overlies the Maastrichtian Owl Creek Formation and is in turn conformably overlain by the Porters Creek Formation. These strata have received little attention because outcrops are few and weathered. A recent study of these sediments in boreholes in New Madrid and Scott counties and a strip mine in Stoddard County yielded abundant macrofossils (mostly invertebrates), foraminifera and palynomorphs. Angiosperm pollen dominate the palynomorph assemblages in all three formations, but dinoflagellate cysts provide a more precise biostratigraphic record for the Clayton Formation, which contains reworked Maastrichtian Cretaceous macrofossils and microfossils. Recovered dinoflagellate cysts include Areoligera senonensis, Cerodinium diebelii, Cerodinium striatum, Cordosphaeridium cantharellum, Palaeocystodinium golzowense, Palaeoperidinium pyrophorum, Senoniasphaera inornata, and Hafniasphaera graciosa, with Senoniasphaera inornata disappearing worldwide during the Danian. Sedimentological characteristics (basal microtektite-bearing coquina grading upward into clay and hardground), poor fossil preservation in the coquinite, and available well log data suggest that the Clayton Formation was likely deposited as short-term, isochronous event resulting from the megatsunami initiated by the Chicxulub impact event.