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 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.

Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum

“…Based on the depth separation between the POE and CIE, the uniform δ 18 O, and a complete sequence of foraminiferal and nannofossil biozones ( 23 , 37 ), it is clear that the records are temporally continuous and unaltered by sediment mixing or slumping. Following the POE, but before the CIE onset, planktonic foraminifera “excursion taxa” appear in the Salisbury Embayment, suggesting a similar ecological and local environment during the latest Paleocene and PETM ( 23 , 38 ). The presence of excursion fauna before the CIE, likely in response to early environmental change and warming ( 13 ), suggests a temporal connection between the POE and the PETM onset.…”

“…S5). During the POE, planktonic foraminifera show evidence of postdepositional partial dissolution as indicated by removal of coarsely cancellate and muricate wall textures, resulting in smooth, thin-walled, and collapsed chambers ( 23 ). Poorly preserved planktonic foraminifera specimens were present in the POE interval, and only the best-preserved specimens were selected for geochemical analysis.…”

“…1 ) ( 19 ). Faunal assemblage data indicate deposition at SDB in deep middle to outer neritic environments during the PETM ( 22 , 23 ). Maryland marine siliciclastic shelf facies during the PETM are characterized by exceptionally high sedimentation rates and less dissolution of carbonate than in deep-sea sections ( 24 ).…”

Diversification of Iron‐Biomineralizing Organisms During the Paleocene‐Eocene Thermal Maximum: Evidence From Quantitative Unmixing of Magnetic Signatures of Conventional and Giant Magnetofossils

“…The PETM is generally characterized by three phases: (1) a pre‐onset excursion (POE) in bulk carbon isotopes, (2) the main carbon isotope excursion (CIE), and (3) a recovery toward baseline, pre‐PETM bulk carbon isotope values. The POE has only been identified in a few study sites (Bowen et al., 2014; Honegger et al., 2020; Luciani et al., 2007; Robinson & Spivey, 2019; Self‐Trail, Powars, et al., 2012; Sluijs et al., 2007). The CIE is sub‐divided into CIE onset and CIE core intervals.…”

Shelf Ecosystems Along the U.S. Atlantic Coastal Plain Prior to and During the Paleocene‐Eocene Thermal Maximum: Insights Into the Stratigraphic Architecture

“…The onset of the CIE at SDB is within a carbonate‐poor interval and is marked by an abrupt decrease of δ 13 C benthic . The interval 204–203 m is barren of calcareous foraminifera (likely due to dissolution; Robinson & Spivey, 2019), thus it does not provide information on the basal part of the PETM. The δ 13 C bulk record is also unreliable for this interval.…”