MICROPALEONTOLOGIC INDICATORS OF ENVIRONMENTAL AND GEOMORPHOLOGIC CHANGE ON THE MID-ATLANTIC SHELF ACROSS THE PALEOCENE-EOCENE THERMAL MAXIMUM (Invited Presentation)

The Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) is recognized in marine sediments around the globe by sedimentological and geochemical perturbations that include a carbonate dissolution zone, the extinction or turnover of benthic foraminifer taxa, and radiation of new planktic foraminifer species. These major changes coincide with the rapid onset of a negative carbon isotope excursion (CIE). The cause and nature of the massive carbon release leading to this extreme climate event remain under debate. Regardless of cause, the environmental and ecological changes centered on the PETM onset provide an imperfect, yet useful analog to modern dynamics related to the increase in atmospheric carbon dioxide and associated ocean acidification.

Analyses of microfossils from the South Dover Bridge and Mattawoman Creek-Billingsley Road coreholes in Maryland and the Wilson Lake and Bass River coreholes in New Jersey provide examples of how shelf ecology can adapt to a massive global carbon perturbation, an enhanced hydrological cycle, and the resulting localized changes in coastal geomorphology. Foraminifera document a surface water perturbation coincident with a minor dissolution event and stressful bottom water conditions as benthic assemblages at different shelf locations become distinct, and planktic assemblages incorporate newly evolved species. Malformed calcareous nannoplankton provide evidence for ecophenotypic response to sea surface warming and eutrophication.

Paleodepth estimates across the region indicate relative sea level changes and are used to reconstruct shelf morphology that defines a late Paleocene depositional center in the central Salisbury Embayment that rapidly accumulated delta sediments in the early Eocene. The slope angle of the shelf along the central axis increases across the PETM onset possibly accompanied by tectonic uplift. Postulated water depth restrictions on the occurrence of Morozovella velascoensis are used as an independent indicator of relative water depth. We present initial bathymetric reconstructions of the Salisbury Embayment before and after the CIE onset and highlight the importance of understanding coastal zone processes when examining shelf sediments.