NEW INSIGHTS INTO SHELF ECOSYSTEMS PRIOR AND DURING THE PETM

We study the South Dover Bridge core (SDB), drilled in the coastal plain of Maryland, in which the Paleocene-Eocene transition is stratigraphically constrained by calcareous nannoplankton. The Paleocene-Eocene Thermal Maximum (PETM) in SDB is characterized by negative δ¹⁸O and δ¹³C excursions within the distinct fine grained unit, known as the Marlboro Clay. The site is situated near the paleo-Potomac River, suggesting that mud deposition during the PETM could be related to intensification of regional river outflow, contrasting with the late Paleocene sediment-starved setting. Stable isotope data show an additional <2 ‰ δ¹³C excursion in a more clayey interval below the PETM-onset, coined the “pre-onset excursion” (POE). This may indicate that the latest Paleocene climate was not as stable as previously assumed, but exhibited a more gradual or stepwise change towards the onset of the PETM.

We generated high-resolution benthic foraminiferal, stable isotope and grain size data to assess the stratigraphy of the Paleocene-Eocene transition at SDB and to correlate the sequence along a depth transect across the paleoshelf, including the New Jersey Coastal Plain. These records allow to constrain environmental changes prior and during the PETM. We observe a shift from well-oxygenated, continuously oligo- to mesotrophic bottom water conditions during the late Paleocene to episodic food fluxes to the seafloor between the POE and the PETM. At the PETM onset, benthic foraminiferal diversity decreases as more stress-resistant taxa become predominant and planktic foraminifera become abundant. This points to periodically dysoxic bottom waters due to nearshore influences in a river-dominated marine setting at SDB. Throughout the later part of the PETM, the succession of foraminiferal assemblages indicates improved oxygen levels. During the PETM recovery phase a return to maintained high food levels and decreased river influence is noticeable. The expanded and extensive SDB sequence in Maryland presents an excellent record of the Paleocene-Eocene transition. As more regional data will become available, these will enable more constrains on environmental parameters and variations along the eastern US Coastal plains.