Crowleys Ridge in southeastern Missouri preserves Cretaceous to Eocene marginal marine sediments deposited in the northwestern portion of the Mississippi Embayment. Sandwiched between the Paleocene Porters Creek Formation and the uppermost Cretaceous Owl Creek Formation is the Paleocene Clayton Formation. Four trenches were excavated and a complete section of Clayton Formation was sampled at a large strip mine in Stoddard County, Missouri. The Clayton at this location consists of 185 cm of graded deposit, the lower part of which includes large Owl Creek rip-up clasts containing layers of microtektites, invertebrate fossils, and abundant terrestrial and marine palynomorphs. Driller's logs and electric logs covering ∼9000 km² were reviewed. Well data confirm the consistent thickness and lithology of the Clayton Formation in this part of the Mississippi Embayment. Based on sedimentological and palynological data from this study, the Clayton Formation in the northwestern Mississippi Embayment appears to be a megatsunami deposit resulting from post-impact effects (early Paleocene) associated with the Chicxulub impact event.