REVISITING THE CRETACEOUS-PALEOGENE BOUNDARY IN WESTERN KENTUCKY, USA

This study revisits a Cretaceous-Paleogene (K-Pg) sedimentary section in western Kentucky to determine the nature of this stratigraphic boundary and the depositional environments. The K-Pg boundary was previously identified at the site based on pollen, but a detailed sedimentological framework remains lacking for the succession and therefore inhibits interpretation of the nature of the boundary. A combination of stratigraphy and sedimentology were used to characterize the section in detail. We relocated the site and measured 1.5 m of section that includes the K-Pg boundary. Four distinct units were identified and from base to top of section are (1) bioturbated black lignitic clay, (2) bioturbated brownish gray mud, (3) gray laminated mud with interlaminated quartz and micaceous sand, and (4) red and yellow mud with laminated sand. The K-Pg boundary is a 5 mm thick layer of Fe-sulfide concretions that commonly exhibit a mammillary surface texture. Fossil wood and amber droplets 2-4 mm wide occur throughout the section. Amber droplets are angular below the boundary in the black lignitic clay facies, but transition to more rounded droplets near the boundary in the brownish gray mud and overlying laminated gray mud. The presence of fossil wood, amber droplets and root traces below the K-Pg boundary suggest the presence of a paleosol weathering in a marsh environment. Above the boundary, the presence of leaf impressions, along with fossil wood and cyclic deposition of mud and sand, suggests a subtidal to intertidal environment. These depositional environments are consistent with the site being situated in a transitional zone along the Mississippi Embayment. Thus far, our work has failed to identify any indicators of a conformable K-Pg boundary (e.g., boundary clay or ejecta spherules) at the site. Ongoing analyses will include petrographic observations, quantitative grain-size and elemental geochemistry.