HR: 0800h
AN: PP41A-0621    [Abstracts]
TI: Provenance of Ice-Rafted Detritus Layers Near the Antarctic Polar Front in the Atlantic Sector of the Southern Ocean
AU: * Nielsen, S H
EM: snielsen@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Hodell, D A
EM: dhodell@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Kanfoush, S L
EM: skanfoush@utica.edu
AF: Department of Geology, Utica College , Utica, NY 13502 United States
AU: Kamenov, G D
EM: kamenov@ufl.edu
AF: Department of Geological Sciences, University of Florida 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Perfit, M R
EM: perfit@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida 241 Williamson Hall, Gainesville, FL 32611 United States
AB: The occurrence of discrete Ice-Rafted Detritus (IRD) layers in the South Atlantic (SA) has challenged the notion of Antarctic ice sheet stability during the last glaciation, yet the exact provenance of these events remains uncertain. SA-IRD events are composed dominantly of volcanic ash and glass and clear mineral grains. The concentration of ash in glacial-aged sediments decreases by more than two orders of magnitude from 53 to 41/deg S with a sharp drop between 53 and 47/deg S, whereas clear mineral grain concentrations decrease in a linear fashion by one order of magnitude from south to north. Ash and clear mineral concentrations are highly correlated with one another at the southernmost site at 53/deg S, but less so at the northern sites where clear mineral abundance exceeds those of ash. We analyzed samples and leachates of volcanic glass and ash from several of the glacial-age SA-IRD events in marine sediment core TN057-13PC4 (ODP Site 1094). The purpose was to establish the provenance of the volcanic glass component of the IRD using rock-forming oxide relative abundances, as well as isotope signatures of strontium, neodymium and lead. The geochemical signatures revealed by microprobe and MC-ICP-MS analysis are almost exclusively similar to those of samples from the South Sandwich Islands (SSI), as well as tentative overlap with volcanics from the Bransfield Strait region. TN057-13 (1094) is downwind and downcurrent from the SSI, but the volcanic grains are too large to be transported that far east from the source by settling through the air and water column. Volcanic glass and ash from the SSI must be ice-rafted to the eastern South Atlantic either by icebergs and/or sea ice. The ash peaks during the last glacial period were accompanied by discrete peaks in clear mineral grains. Microprobe analyses of some of these minerals, previously identified as quartz, reveal a mixture of Ca-plagioclase, orthopyroxene, and quartz. Anorthite and orthopyroxene are common phenocrysts in SSI pumice, which could explain their occurrence with SSI-derived ash; however, preliminary Sr-, Nd- and Pb-isotope geochemical analysis of some of the feldspars suggests an origin from a Paleoproterozoic, Antarctic source. Additional geochemical analysis should elucidate the provenance of these clear mineral grains and their significance for Antarctic ice-sheet dynamics.
DE: 3022 Marine sediments: processes and transport
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4926 Glacial
DE: 8404 Volcanoclastic deposits
DE: 9310 Antarctica (4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005