LESSONS LEARNED FROM TRANSGRESSIVE PALEOZOIC SANDSTONES AND MODERN MID-ATLANTIC BARRIER ISLANDS, CHINCOTEAGUE BAY REGION, VIRGINIA: IMPLICATIONS FOR LAND USE AND MANAGEMENT PLANNING IN THE FACE OF SEA-LEVEL RISE

The geologic record contains evidence of quartz-rich, fossiliferous sandstones deposited in passive margin environments during periods of sea level rise. Examples from the Paleozoic of the Eastern US include the Ordovician St. Peter, Silurian Tuscarora, and Devonian Oriskany sandstones. In sequence stratigraphic nomenclature these are transgressive systems tract (TST) deposits and have been traced 1000’s of square miles. Capped by offshore mudstones and limestones, each has been attributed to Milankovitch cycles, and estimates indicate these to have been deposited with sea level rise (SLR) rates of <1mm/year. Workers have suggested these to be “time-rich” with evidence of extensive reworking by storms. Given these time scales, the relatively low rates of SLR, and the fact that early-mid Paleozoic landscapes lacked vegetation critical in the function of analogous modern environments, it is challenging to fully equate these ancient deposits to the accepted modern analogs. In particular the modern analogs, i.e. nearshore barrier island (BI) and shallow shelf environments, are experiencing significantly higher rates of SLR approaching 3 mm/year (over 3 times the accepted rates for the Paleozoic). Nevertheless, the past may still be prologue as BIs are responding to SLR by migrating landward at >5-7m/yr by seaward erosion and storm-induced roll over. Ongoing sedimentologic and dendroecological investigations of Wallops and Assateague (WI and AI) barrier islands over the last decade, in partnership with NASA Wallops and the Chincoteague National Wildlife Refuge, provide insights that are pertinent to management planning to improve resiliency in the face of climate change impacts as well as SLR. New data is especially critical in that BI’s are both losing height and are losing sediment to the offshore where it is lost to the littoral zone as a result of closely-spaced storm events. Likewise healthy barrier island forests are ghosting as alkaline salt water and expanding wetlands contribute to their decline. Maritime forest losses will undoubtedly increase migration rates and jeopardize coastal communities. SLOSH and SLAMM modeling demonstrates pronounced impacts within immediate decades.