Environmental and Geomorphological Changes on the Eastern North American Continental Shelf Across the Paleocene-Eocene Boundary

摘要

Foraminiferal evidence from two sites in southern Maryland, eastern United States, reveals a series of rapid environmental changes on the continental shelf during the onset of the Paleocene-Eocene Thermal Maximum (PETM). Benthic and planktic foraminifer assemblages from the South Dover Bridge and Mattawoman Creek-Billingsley Road coreholes in the central Salisbury Embayment record changing latest Paleocene and earliest Eocene environmental conditions that began prior to the carbon isotope excursion that marks the beginning of the PETM. The foraminiferal response reflects increases in productivity in the bottom water, a minor dissolution event, and sea surface warming in the latest Paleocene. Relative sea level changes, a sudden change in sedimentary regime, and a decrease in bottom water oxygenation occurred in this region across the PETM onset. While South Dover Bridge assemblages support a rise in sea level across the PETM onset, Mattawoman Creek-Billingsley Road assemblages record a reduction in water depth interpreted as delta progradation and possible tectonic activity. Transitional carbon isotope values are recorded in these delta sediments. We present an initial bathymetric reconstruction of the Salisbury Embayment showing the physical effects of the carbon isotope excursion onset on shelf morphology and highlight the importance of understanding coastal zone processes when examining shelf sediments.