HR: 0800h
AN: OS51B-0567    [Abstracts]
TI: Holocene record of deglaciation on the Chukchi Shelf, offshore NW Alaska
AU: * Hill, J C
EM: jchill@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0208
AU: Driscoll, N W
EM: ndriscoll@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0208
AU: Donnelly, J P
EM: jdonnelly@whoi.edu
AF: Woods Hole Oceanographic Institution, Geology and Geophysics Department, Woods Hole, MA 02543
AB: Holocene sediments on the Chukchi shelf record a complex history of fluvial discharge, glacial meltwater, sea ice, and sea level fluctuations. A series of piston cores collected across the shelf, in combination with high resolution chirp seismic profiles reveal differing patterns of sedimentation and highlight the role of paleoclimatic variability in the region. The inner shelf is dominated by buried paleochannels within a large incised valley, on the order of ~20 km and 45 m deep, which appear to be carved by fluvial processes over multiple sea level cycles and massive glacial discharge following the Last Glacial Maximum (LGM). The sediments collected in the SW part of the valley are well sorted, fine sand with silty clay rip-up clasts at the base, grading upward into interbedded silty clay and sand, with marine clay at the top. These sediment facies, along with evidence from the chirp seismic profiles suggest an episode of high discharge and consequent incision. Estimates from both the inner shelf and the Hope Valley to the south indicate a dramatic decrease in sedimentation at approximately 6 ka from 1.5 mm/yr to less than 0.1 mm/yr, which is consistent with waning glacial discharge. Very negative 18O values around ~11ka from the Hope Valley core also suggest large volumes of glacially derived freshwater input. Sediments collected in the NE part of the valley are extensively interbedded sequences of fine sand grading into silty clay, interpreted as marine sediment overlying fluvial deposits in response to the Holocene relative sea level rise. Sediments on the mid and outershelf were collected from layers infilling small, isolated paleochannels and ice scour depressions. These sediments, while not as visibly interbedded as those on the innershelf, show distinct, cyclical fluctuations in the coarse fraction (>63 μm), along with marked changes in mineralogical assemblages and pulses of reworked benthic foraminifera, suggestive of seasonal variations in sea ice cover over the last 10 kyrs. The sedimentation history of the Chukchi Shelf appears to record deglaciation on the NW Alaskan margin with the dominant sediment input derived from large volumes of fresh water immediately following the LGM, shifting to a system affected by icebergs scour, and culminating in depositional cycles controlled to some degree by seasonal sea ice and productivity.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005