Environmental and geomorphological changes on the eastern North American Continental Shelf across the Paleocene-Eocene Boundary

Abstract

Foraminiferal evidence from two sites in southern Maryland, eastern United States, reveals a series of rapid ecological 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 (SDB) and Mattawoman Creek-Billingsley Road (MCBR) cores in the central Salisbury Embayment record changing latest Paleocene and earliest Eocene ecological conditions that began prior to the carbon isotope excursion (CIE) that marks the beginning of the PETM. The foraminiferal response reflects increases in productivity first in bottom water and then in the mixed layer, a minor dissolution event, and rising sea-surface temperatures in the latest Paleocene. Relative sea level changes, a sudden change in sedimentary regime, a decrease in bottom water oxygenation, and a downward expansion of the mixed layer occurred across the PETM onset. In the earliest Eocene, foraminiferal assemblages document a gradual shallowing of the thermocline and/or cooling of the surface layer. While SDB assemblages support a rise in sea level across the PETM onset, MCBR assemblages record a drop in sea level interpreted as delta progradation. Transitional carbon isotope values characterizing the nature of the CIE are recorded in these delta sediments. We present an initial bathymetric reconstruction of the Salisbury Embayment showing the physical effects of the CIE onset on shelf morphology and highlight the importance of understanding coastal zone processes when examining shelf sediments.