Paleoceanographic Cause for Nannofossil Biostratigraphic Discordance between Adjacent Nearshore and Deepwater Localities in the Upper Maastricthian of the Atlantic Margin, Southern United States

Watkins, David K.¹, Jean M. Self-Trail² (1) University of Nebraska, Lincoln, NE (2) United States Geological Survey, Reston, VA

Paleoecologic and paleoceanographic variations in the nature of the oceanic surface water masses can influence significantly the validity of biostratigraphic correlation and its integration into geological models that span multiple depositional environments. This problem may be especially acute when comparing nearshore, shelfal localities with those in adjacent deepwater areas. This is illustrated by recent studies that compare upper Maastrichtian sequences from eight cores on the South Carolina Coastal Plain with two cores from the adjacent continental slope. The biostratigraphic sequences from the Coastal Plain cores are internally consistent and yield a coherent succession of calcareous nannofossil biohorizons. Similarly, the continental slope cores yield a consistent and coherent biostratigraphic succession of nannofossils. Although the two sets of localities are separated by only about 500 km, they cannot be correlated easily using nannofossils. There is a high crossover frequency of the stratigraphic positions of biostratigraphic datums (first and last appearances) between the coastal plain and continental slope localities, and several of the major biostratigraphic markers occur only in one or the other sample sets. Paleoecological analysis indicates that there are significant differences in species composition and paleocommunity structure between the two sets that transcend set-specific, short-term variations within each set. Multivariate analyses indicate a strong thermal contrast between the surface waters of the coastal plain and continental slope, with the slope assemblages reflecting significantly higher paleotemperatures. These analyses indicate that the presence of a late Maastrichtian Gulf Stream segregated the nannofossil populations, resulting in significant complications in correlation between these adjacent localities.