SIGNIFICANCE OF MARINE OXYGEN ISOTOPE STAGE OIS5a AND OIS3 OSL DATES FROM ESTUARINE SEDIMENTS FLANKING CHESAPEAKE BAY

Numerous outcrops of late Quaternary estuarine-to-fluvial sediments flank tributaries to Chesapeake Bay. Sediments up to 5 meters above present sea level are dated at 91+/-14 ka to 65+/-9 ka by optically stimulated luminescence (OSL). A core from Hybla Valley, a paleo-tributary to the Potomac River, contains sands at 5m above present sea level dated at 84 +/-9 ka by OSL. These dates are significantly younger than OIS5e (~125ka), and older than OIS3 (60-28ka). They fall within OIS5a (90-72ka), and possibly OIS4 (72-60ka). U-series dates from corals in the vicinity of Chesapeake Bay show that a marine transgression higher than present sea level occurred during OIS5a, well after OIS5e. Outcrops on the Chester River and Potomac River also have 2-to-5m thick estuarine units with OSL dates that fall within OIS3. OSL dates as young as ~35ka from marine barriers in North Carolina also indicate sea level highstands as young as late OIS3 at higher than present mean sea level. The youngest OIS3 estuarine units dated in this study are overlain by dune sands that date to ~32ka. The ages of late Quaternary transgressive units between ~90ka and ~32ka flanking Chesapake Bay cannot be explained simply as a response to eustatic sea level variations. The age/elevation trend of these deposits is inversely related to the published global sea level curves for that period. This stratigraphic relation is best explained by subsidence during the period from ~100ka to ~32ka, and subsequent uplift to >5m above present sea level. We argue that uplift was a due to forebulge that developed in response to the rapid and extensive growth of the Laurentide Ice Sheet.