Abstract:
IODP Exp. 313 drilled a transect of boreholes on the NJ inner continental shelf to examine the complex relationships between global sea level change and margin sedimentation. Micropaleontological data are key to reconstructing sea level history; benthic foraminifera provide paleodepth estimates and palynological data (dinocyst/pollen ratio, D/P) provide distance-from-shoreline estimates. In general, these show close agreement in Exp. 313 boreholes. Pollen data can also reflect nearby continental climate, as wind-blown pollen is deposited offshore. In the Exp. 313 boreholes, an interval of increased hemlock (Tsuga) pollen abundances indicates cooler, wetter conditions in this region approximately 18-21.5 Ma (peak values approximately 20-21 Ma). In this study, we use benthic foraminiferal assemblages to reconstruct paleobathymetry during this time. Our goal is to examine the relationship between sea-level change (indicated by benthic foraminifera and D/P) and climate conditions in eastern North America (indicated by fossil pollen). Benthic foraminiferal species typically colonize certain water depth ranges, with key depth-indicator species providing the means to reconstruct paleobathymetry. We estimated paleodepths at Sites 27A and 29A primarily based on faunas characterized by various species of Hanzawaia, Pseudononion, Buliminella, Uvigerina, Cibicidoides, and/or Oridorsalis. The hemlock interval at Site 29A (Cores 198-217) spans several seismic surfaces, with benthic foraminiferal assemblages indicating several deepening and shallowing intervals through the section. Peak hemlock abundances at Site 29A (Cores 208-209) correspond to a shallow interval indicated by benthic foraminifera. The hemlock interval at Site 27A (Cores 150-154) is restricted to a narrower time interval, and benthic foraminiferal assemblages indicate a deepening, consistent with D/P. Our data indicate that there was no direct correlation between regional climate conditions in the NJ hinterland and sea level for the time interval approximately 18-21.5 Ma. This indicates that the wet, cool conditions in the hinterland (indicated by hemlock) are probably a regional phenomenon not linked to ice-sheet expansion and sea-level change.