HR: 1340h
AN: PP13B-1277    [Abstracts]
TI: The Flooding of Long Island Sound
AU: * Thomas, E
EM: ellen.thomas@yale.edu
AF: Yale University, Geology and Geophysics, PO Box 208109, New Haven, CT 06520-8109, United States
AU: * Thomas, E
EM: ellen.thomas@yale.edu
AF: Wesleyan University, E & ES, 265 Church Street, Middletown, CT 06459, United States
AU: Varekamp, J C
EM: jvarekamp@wesleyan.edu
AF: Wesleyan University, E & ES, 265 Church Street, Middletown, CT 06459, United States
AU: Lewis, R S
EM: ralph.s.lewis@uconn.edu
AF: University of Connecticut Marine Sciences, 1080 Shennecossett Road, Groton, CT 06340, United States
AB: Between the Last Glacial Maximum (22-19 ka) and the Holocene (10 ka) regions marginal to the Laurentide Ice Sheets saw complex environmental changes from moraines to lake basins to dry land to estuaries and marginal ocean basins, as a result of the interplay between the topography of moraines formed at the maximum extent and during stages of the retreat of the ice sheet, regional glacial rebound, and global eustatic sea level rise. In New England, the history of deglaciation and relative sea level rise has been studied extensively, and the sequence of events has been documented in detail. The Laurentide Ice Sheet reached its maximum extent (Long Island) at 21.3-20.4 ka according to radiocarbon dating (calibrated ages), 19.0-18.4 ka according to radionuclide dating. Periglacial Lake Connecticut formed behind the moraines in what is now the Long Island Sound Basin. The lake drained through the moraine at its eastern end. Seismic records show that a fluvial system was cut into the exposed lake beds, and a wave-cut unconformity was produced during the marine flooding, which has been inferred to have occurred at about 15.5 ka (Melt Water Pulse 1A) through correlation with dated events on land. Vibracores from eastern Long Island Sound penetrate the unconformity and contain red, varved lake beds overlain by marine grey sands and silts with a dense concentration of oysters in life position above the erosional contact. The marine sediments consist of intertidal to shallow subtidal deposits with oysters, shallow-water foraminifera and litoral diatoms, overlain by somewhat laminated sandy silts, in turn overlain by coarser-grained, sandy to silty sediments with reworked foraminifera and bivalve fragments. The latter may have been deposited in a sand-wave environment as present today at the core locations. We provide direct age control of the transgression with 30 radiocarbon dates on oysters, and compared the ages with those obtained on macrophytes and bulk organic carbon in the same samples (calibrated with CALIB 5.1 using the Intcal 04 data set). The carbonate ages for most samples are considerably younger than those of the bulk carbon and plant fragments: the organic matter must have resided on land, possibly stored in periglacial lake beds, for up to several millennia prior to deposition in Long Island Sound. The carbonate ages indicate that the main marine transgression occurred at 11-10 ka, at the end of the Younger Dryas (Melt Water Pulse 1B), when glacial rebound was waning and the rate of sea level rise accelerated. It is possible that earlier inundation led to deposition of estuarine clays in deeply incised channels. We estimate that the maximum crustal depression of Long Island Sound was about 40 m, and rebound started at about 15 ka (Melt Water Pulse 1A). We thus conclude that Long Island Sound became a marine estuary at the beginning of the Holocene, much later than had been assumed. The earliest native Americans reached the area during the Younger Dryas and may have witnessed the relatively rapid inundation by the sea of a large section of the Long Island Sound basin.
UR: http://ethomas.web.wesleyan.edu/lisweb
DE: 1105 Quaternary geochronology
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 4235 Estuarine processes (0442)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting