TIMELINE OF ENVIRONMENTAL AND GEOMORPHOLOGICAL CHANGE ACROSS THE PALEOCENE-EOCENE BOUNDARY FROM HIGH-RESOLUTION STUDIES OF THE SHALLOW MARYLAND SHELF

Foraminiferal and sedimentological analyses from two marine sites in southern Maryland reveal a series of rapid environmental changes on the shallow 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 record changing environmental conditions that began prior to the carbon isotope excursion (CIE) that marks the PETM onset. We present high-resolution foraminiferal evidence of the rapidly changing conditions in the central part of the Salisbury Embayment, where PETM sediments are the thickest. We focus on sediments from the Paleocene-Eocene boundary, recording the conditions immediately before, during and immediately after the CIE onset. Combined data from SDB and MCBR produce a nearly continuous composite record of changing environmental conditions caused, at least in part, by the enhancement of the local hydrological regime and increase in sediment accumulation rate.

Microfossil evidence documents a surface water perturbation in the latest Paleocene coincident with a minor dissolution event and followed by increasingly stressful bottom water conditions prior to the PETM onset. 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 SDB assemblages support a rise in relative sea level across the PETM onset, MCBR assemblages record a reduction in water depth interpreted as delta progradation. A regional decrease in bottom water oxygenation follows the PETM onset as benthic assemblages at different shelf locations become distinct, and planktic assemblages incorporate newly evolved species.

The foraminiferal assemblages from these two sites document the order in which this shelf ecosystem responded to the rapidly changing environment associated with the massive global carbon perturbation and add to the growing body of research characterizing the PETM shelf environment.