EARLY HOLOCENE MARSH FORAMINIFERA AND OSTRACODES FROM CHESAPEAKE BAY: IMPLICATIONS FOR SEA-LEVEL HISTORY

The relationship between the final phase of post-glacial sea-level rise ~ 9.0-7.5 ka and Laurentide and Antarctic ice sheet decay and glacial lake drainage is critical for understanding the cause of the 8.2 ka global cooling event. However, the magnitude and rate of Holocene sea-level rise is poorly constrained due to uncertainties in chronology and ecology of fossil coral reefs. Sediment cores taken on the R/V Marion-Dufresne at water depths between 8 and 30 m below sea level (mbsl) recovered a detailed record of the early Holocene continental-estuarine transition caused by glacio-eustatic sea-level rise. Radiocarbon-dated sediments from several cores contain foraminifera and ostracodes, which can be used to accurately constrain sea-level positions before and after the 8.2 ka event. The foraminifers Trochammina macrescens, T. inflata, Ammoastuta sp., and Haplophragmoides sp. and ostracodes Cyprideis, Cytheromorpha fuscata and C. curta, which live today intertidally in Spartina marshes along Chesapeake Bay and elsewhere in eastern North America, dominate early Holocene Chesapeake Bay sediments between 24 and 45 mbsl. By correcting the depths of early Holocene intertidal marsh sediments for mean post-glacial isostatic uplift of ~ 1.5 mm per year for the Chesapeake region, we obtained estimates of the rate of sea-level rise ranging from a minimum of 8 to a maximum of 30 mm per year between ~ 9.0 and 7.7 ka.