Austrian Journal of Earth Sciences vol:105 issue:1 pages:169-178
Climate and Biota of the Early Paleogene edition:2012 location:Salzburg date:5-8 June 2011
Chemostratigraphic and biostratigraphic studies of Paleocene-Eocene boundary sequences in the New Jersey Coastal Plain reveal that the Paleocene-Eocene thermal maximum (PETM) corresponds to a basin-wide, thick clay unit. Benthic foraminifera have been studied at low resolution, but we present the first high-resolution benthic foraminiferal data and paleoecologic interpretations of the more landward Wilson Lake and more seaward Bass River drill sites. Graphic correlation allows refinement of the site-to-site correlation, providing insight in the succession and timing of environmental changes associated with the onset of the PETM. Uppermost Paleocene glauconitic sandy strata were deposited at very low sedimentation rates (Bass River ~ 1 cm/kyr and Wilson Lake ~ 0.1 cm/kyr). Deposition occurred in stable, well-oxygenated deep middle neritic (Wilson Lake,) to outer neritic environments (Bass River). No changes in benthic assemblages are associated with the start of the Apectodinium acme or the proposed pre-PETM sea surface temperature rise. The onset of the PETM, as characterized by the base of the carbon isotope excursion (CIE), is at the transition from glauconitic sands to silty clay, coinciding with a major benthic foraminiferal change towards a more outer neritic assemblage consisting of opportunistic taxa. The onset of the PETM is represented in a transitional fauna present in the updip Wilson Lake site (sedimentation rate ~ 16.9 cm/kyr), whereas the more downdip section (Bass River) contains a relatively condensed interval (sedimentation rate ~ 2.8 cm/kyr). In the record from the expanded Wilson Lake sequence, the start of a major sea level rise coincided with the onset of the CIE and preceded the establishment of the dysoxic eutrophic conditions in the earliest PETM as indicated by the low-diversity, opportunist dominated benthic foraminiferal assemblages. This low-diverse assemblage probably reflects the establishment of persistent stratification and subsequent dysoxic sea floor conditions. Increasing benthic diversity indicates a steady environmental recovery later in the PETM, during which seasonal dysoxic eutrophic conditions still created periodic stress for the benthic biota. Site-to-site correlation indicates an increase in sedimentation rates for this interval (Wilson Lake ~ ≥21.4 cm/kyr and Bass River ~ ≥10.0 cm/kyr), in association with high influxes of low-salinity tolerant dinoflagellates. Overall, benthic communities indicate no environmental changes prior to the PETM and the rapid development of a stratified water column during the PETM, leading to permanent dysoxic bottom water conditions, followed by a gradual decline in stratification and only seasonal dysoxia.