UPPER CRETACEOUS TO PLIOCENE CHANGES IN SEDIMENT PROVENANCE, A DETRITAL-ZIRCON GEOCHRONOLOGICAL ANALYSIS OF UPPER COASTAL PLAIN SEDIMENTS FROM SOUTH CAROLINA

Understanding the sources of sediments is a foundational aspect of sedimentary geology. Sediment provenance studies can yield tremendous insight into reconstructing Earth history, providing valuable data about tectonic processes, paleoenvironmental and paleoclimatic conditions, and sediment transport pathways. While much work has been done to characterize the lithology, stratigraphy, and depositional settings of Upper Coastal Plain deposits in South Carolina, a significant opportunity exists to better understand where these sediments came from and how sediment sourcing may have changed over time. To that end, we obtained sediments from an Upper Coastal Plain core from the South Carolina Geological Survey. Eight samples, spanning units of upper Cretaceous to Pliocene ages, were analyzed by laser-ablation U-Pb detrital-zircon geochronology. Our samples contain zircons with a variety of ages, with age nodes centered ca. 400 Ma (Early Paleozoic), 1050 Ma, and 1150 Ma (Mesoproterozoic). Age population distributions tend to vary between the Pliocene Duplin Formation and the underlying middle Eocene Warley Hill, upper Paleocene Lang Syne, and upper Cretaceous Sawdust Landing formations. Duplin Formation samples contain abundant Paleozoic-aged zircons, low amounts of Neoproterozoic zircons, and moderate to high amounts of Mesoproterozoic-aged zircons increasing to ~50% at the base of the unit. By contrast, detrital-zircon age populations within the Warley Hill, Lang Syne, and Sawdust Landing formations, are characterized by a dearth of Mesoproterozoic-aged zircons (~3%), generally a slightly greater abundance of Neoproterozoic zircons, and are otherwise comprised of zircons almost exclusively of Paleozoic ages. These results suggest that the sources of sediments to this portion of the Upper Coastal Plain were fundamentally different prior to the Pliocene. Potential causes for this difference could be a greater surficial exposure of Mesoproterozoic-aged rocks during the Pliocene, or perhaps a change in paleodrainage patterns that provided access to zircons of this age.