Late quaternary paleoecology and heinrich events at gray's Reef national marine sanctuary, South Atlantic bight, Georgia

摘要

The use of palynofacies as a conceptual tool for the study of depositional environments augments and extends the pointsource studies using geophysical, lithological correlation and microfossil analyses of sediment cores in the offshore. We present a synthesis of palynofacies research in the South Atlantic Bight/Georgia Bight, USA. Two research localities - Gray's Reef National Marine Sanctuary (GRNMS) and nearby J-Reef - on the same (-20 m) isobath and only 16 km distant form one another, were characterized in our study. Vibracores to over 4 m below the sea floor were taken at both locations together with hand cores. Outcrops and seafloor exposures were hand sampled. These data are varied and, synthesized elsewhere, yielded insights into the Quaternary paleoenvironments of the coastal plain. Nearshore marine, barrier-back barrier, estuarine- marsh and upland biota provide geologic and ecologic proxies in the form of micro and macrobotanical remains - to include pollen, spores, diatoms, foraminifera and wood. The use of several techniques, notably optical stimulated luminescence (OSL), accelerator mass spectroscopic-radiocarbon (AMS-RC), amino acid racemization (AAR), and uranium series dating methods) has produced a presumptive chronostratigraphy that extends from the Holocene to oxygen isotope stage (M.I.S.) 5. Models based on our pollen results are compared to others proposed for the Mid-Atlantic and Southeast Atlantic regions of the Atlantic coastal plain. Analyses-sedimentological, geophysical, paleoecological and chronological-in the area of Gray's Reef National Marine Sanctuary (GRNMS), have increased our understanding of the late Pleistocene paleoecology and that of relative sea level (RSL) for the now drowned Atlantic Coastal Plain. Palynological data provide a clearer picture of the ecology of the Atlantic Coastal Plain in the latter Pleistocene Epoch, M.I.S.5 through and post-Last Glacial Maximum (LGM/M.I.S.2/Holocene). Arboreal species, notably oak and pine, dominate the pollen spectra and show clear climate-related variability most notably with Heinrich Events.