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Early Holocene Sea-Level Rise and Origin of Chesapeake Bay
Chesapeake Bay is the largest estuary in the United States with a mean depth of ~8 m and a deep channel 20-50 m deep. The main channel is a remnant of incomplete sediment infilling of the Susquehanna River paleochannel, which was excavated to ca. 50-55 mbsl during the last glacial maximum. Depending on location, approximately 10 - 25 m of Holocene sediments overlie the Cape Charles erosion surface (CCES) formed during glacial low sea level. The bay is well suited to study sea-level variability because regional vertical tectonic movements are negligible. Sea level is currently rising in the bay at about 3.5 mm yr-1, about half of which is due to post-glacial isostatic adjustment in the collapsing forebulge region of the Mid-Atlantic region United States. A mean rate of Holocene isostatic subsidence of ~1.5-1.6 mm yr-1 is known for the Mid-Atlantic region from sea-level curves constructed from radiocarbon-dated basal peats from the Delaware coast and Chesapeake Bay, analyses of tide gauge and radiocarbon-dated sea level curves (Peltier, 1996), and comparison between GPS satellite and tide gauge data.
Studies of Holocene sea-level in Chesapeake Bay use radiocarbon dating of fossil wood and oysters, coastal marsh sediments, oysters, mollusks, and foraminifera to reconstruct sea level history. These studies reveal that age of the flooding of the paleo-channel was between 9.5 and 6 ka, however it is not known if initial flooding of the bay was caused by rapid sea-level rise or the breaching of a sill in the southern bay near its mouth. Evidence from several lines of evidence obtained from sediment cores and geophysical data in the bay indicate that a rapid sea level rise between ~9.0 and 7.5 ka may have been responsible for flooding the bay. Investigations into cores taken in 1999 and 2003 by the Marion-Dufresne are examining the early Holocene evolution of the bay and its relationship to global sea level and climate and melting ice sheets.
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