STRATIGRAPHIC IMPLICATIONS OF RHYTHMITES WITHIN THE UPPER MAASTRICHTIAN PRAIRIE BLUFF CHALK ALONG THE EASTERN MISSISSIPPI EMBAYMENT

Upper Cretaceous shallow marine deposits are well exposed in the Gulf Coastal Plain (GCP). These successions represent mixed carbonate-siliciclastic marginal marine to shallow shelf depositional environments. In Mississippi and Alabama, the upper Maastrichtian Prairie Bluff Chalk records sequences of decimeter scale alternating chalk and marl. These rhythmites record cyclical variations in Earth’s climate leading up to the K/Pg mass extinction event. Lithologic and stable isotope analyses have not been previously used to aid in paleoenvironmental and chronologic interpretations of latest Maastrichtian deposits in the GCP. In this study, we utilize lithological and stable isotope data as well as the recently published ammonite biostratigraphy of the GCP to refine the timing and nature of climatic events, which may be associated with insolation changes that resulted from the Milankovitch cycles. Samples were systematically collected every 20 cm throughout three uppermost Maastrichtian sections (Starkville and Fort Deposit in Alabama, and Houston in Mississippi) for bulk carbon and oxygen isotope (δ¹³C, δ¹⁸O) analyses. Preliminary data suggest δ¹³C values show patterns that closely match cyclical changes in lithology. This analysis, in conjunction with the detailed biostratigraphy of the area, could improve the temporal resolution and provide important information regarding paleoenvironmental changes leading up to the K/Pg mass extinction event.