Paleocene–Eocene Thermal Maximum environmental change in the New Jersey Coastal Plain: benthic foraminiferal biotic events

Abstract

The environmental impact of the Paleocene–Eocene Thermal Maximum (PETM) has been intensively studied in the New Jersey Coastal Plain, but the benthic foraminiferal response, reflecting bottom water conditions, has not been documented at high resolution. We use benthic foraminiferal data across the Paleocene–Eocene boundary in cores from Wilson Lake (WL) and Bass River (BR) to recognize 5 foraminiferal associations (based on species clusters). Their varying abundances allow the identification of a stratigraphic succession of 8 distinct biofacies across the studied interval. Uppermost Paleocene biofacies 1 corresponds to the glauconitic sands of the Vincentown Formation and contains rare, small planktic foraminifera and a diverse benthic fauna. Sediments accumulated slowly in a sufficiently oxygenated, outer neritic setting (depth: 100–110 m at WL, 140–150 m at BR) under fairly oligotrophic conditions. The embayment was storm-dominated and influenced by strong currents, inhibiting deposition of suspended fine particles (e.g., planktic foraminifera, clay) and enhancing re-suspension. No significant pre-PETM environmental changes are detected in the benthic foraminiferal assemblages. Deposition of the fine-grained silty clays of the Marlboro Clay started at the onset of the PETM, with transitional lithology present at Wilson Lake. Gavelinella beccariiformis, common at deep shelfal to bathyal-abyssal depths, is the only taxon to become extinct at this level. Water depth increased during the PETM to a maximum of 130–150 m at WL. Planktic foraminifera increased strongly in abundance, while the benthic foraminiferal assemblage changed to a more opportunistic, less diverse assemblage dominated by stress-tolerant taxa (Tappanina selmensis, Pulsiphonina prima and Anomalinoides acutus, biofacies 2). Increased riverine influence may have reduced vertical mixing, initiating stratification of the water column, and establishment of a continuously dysoxic mud belt. Benthic diversity then gradually increased, indicating environmental recovery (biofacies 3 and 4; 40–95 kyr post PETM-onset). Riverine influence probably became more variable, generating peak abundances of specialized taxa in a mud belt system with increased accumulation rates. The latest PETM biofacies 5 (> 95 kyr post-onset) contains a poorly diverse Bulimina callahani assemblage, indicative of reoxygenated, but still eutrophic bottom water conditions, with renewed vertical mixing. The lower Eocene glauconitic sandy clays of the Manasquan Formation contain an outer neritic benthic fauna (biofacies 6–8, depth: 100–135 m at WL) indicative of persistent high primary production, with return of more vigorous currents. Higher abundances of buliminids may have been triggered by upwelling along frontal zones. Our environmental interpretations indicate relatively stable benthic foraminiferal ecosystems at persistently outer neritic water depths (100–150 m), despite distinct temporary changes during the PETM, including eustatic sea-level rise of up to ~ 30 m, and widespread establishment of dysoxic conditions.