Sedimentary deposits in Stoddard County, southeastern Missouri, reveal a K-Pg transition sequence represented by the uppermost Maastrichtian Owl Creek Formation and the Paleocene Clayton Formation. The Clayton Formation is characterized by a basal fossiliferous coquinite that contains reworked late Maastrichtian macrofossils. Dinoflagellate biostratigraphy is used to determine the age of the coquinite layer and specifically whether or not it is an end-K tsunamite deposit resulting from the Chicxulub impact event. Results indicate a mixed assemblage of late Maastrichtian and early Danian dinocysts within the basal coquinite of the Clayton Formation. Maastrichtian dinocyst taxa identified are Riculacysta amplexa, Pierceites pentagonus, Phelodinium tricuspe and Dinogymnium sp. and dinocysts utilized as global indicators of the basal Danian, also present in the coquinite, consist of Senoniasphaera inornata, Carpatella cornuta, Damassadinium californicum, and Lanternosphaeridium reinhardtii. A gray mud occurring above the coquinite in the middle of the Clayton Formation contains the mid-Danian dinoflagellate Senegalinium iterlaaense. Collectively, these data suggest that the coquinite was deposited well after the K-Pg event but before the middle Danian. The mixed assemblage of Late Cretaceous and Paleocene dinocysts preserved in the coquinite weakens the hypothesis that it is an end-K tsunamite deposit and suggests instead that it may result from a long-term transgressive lag. We also extend the stratigraphic range of the Paleocene Senegalinium simplex downward into the uppermost Maastrichtian.