HR: 15:15h
AN: H33E-05    [Abstracts]
TI: Tracing Provenance of Antarctic Glacio-marine Sediment Through Radiogenic Isotopes, Ar/Ar Hornblende Ages, and Bulk Geochemistry
AU: * Brachfeld, S
EM: brachfelds@mail.montclair.edu
AF: Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, United States
AU: van de Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, NY 10964, United States
AU: Hemming, S
EM: sidney@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, NY 10964, United States
AU: Goldstein, S L
EM: Steven Goldstein
AF: Lamont Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, NY 10964, United States
AU: Roy, M
EM: roy.martin@uqam.ca
AF: Départment des Sciences de la Terre ét de l'Atmosphère, Université du Québec à Montréal, Montréal, Canada
AU: Gorring, M
EM: gorringm@mail.montclair.edu
AF: Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, United States
AU: Williams, T
EM: trevor@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, NY 10964, United States
AB: We are applying a suite of sediment provenance tracing techniques to Antarctic marine diamict samples. The composition of sediments derived from the glacial erosion of Antarctica provides an important framework for evaluating iceberg contributions to the ocean over time. We targeted glacial diamict samples where available, or sandy mud otherwise. This strategy ensures sampling and homogenization over large areas, avoids possible biasing in limited and heterogeneous outcrops, and avoids the competing influences of sediment redistribution by ocean currents. When completed, this ongoing study will provide an integrated characterization of the lithologic clast composition, bulk sediment geochemistry, iron oxide mineralogy and geochemistry, Ar/Ar ages of hornblende grains, and radiogenic isotope signatures of a circum-Antarctic sample set. This approach will allow the identification of the geographic regions from which Antarctic sediment was supplied to the Southern Ocean, and thus constrain ice sheet dynamics and behavior of surface currents. Ice proximal samples from West Antarctica, East Antarctica and the Antarctic Peninsula were collected from fjords, bays, and inner shelf basins. Subsamples were taken from piston cores, kasten cores, and surface grabs collected over the past 40 years by the U.S. Antarctic Program. Here we present preliminary results from the Wilkes Land margin, Marie Byrd Land, and the western Antarctic Peninsula, which constitute an Archean craton, Paleozoic to Cenozoic sequences, and a mixed though relatively younger bedrock geology, respectively. The Nd isotope composition of the < 63- micron fraction generally conforms to the results from a survey of circum-Antarctic distal samples (Roy et al., Chemical Geology, submitted). However, the George V Coast samples (143 E longitude) yielded eNd values of approximately -24, the lowest values yet found in our survey, implying very old Nd crustal residence ages. The hornblende grains from these East Antarctic samples are irradiated and analyses are underway. The Roy et al. survey indicates that sediments from Wilkes Land are distinct from the rest of East Antarctic samples, with large peaks in the age spectrum at 1500-1800 Ma and 1100-1300 Ma, smaller peaks at ~400-600 Ma and 0-200 Ma. Ar/Ar ages of individual hornblendes separated from diamict samples from the West Antarctic margin and Antarctic Peninsula geologic terranes are younger than 250 Ma, and they cluster in populations that are distinct in different areas. Other analyses in progress include lithological clast identification, bulk geochemistry of the <63-micron fraction, and geochemical fingerprinting of detrital iron oxide grains. Accordingly it appears that with a more comprehensive survey it may be possible to discern in detail the regional contributions from different flow lines within Antarctica's ice sheets.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1040 Radiogenic isotope geochemistry
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1100 GEOCHRONOLOGY
DE: 9310 Antarctica (4207)
SC: Hydrology [H]
MN: 2007 Joint Assembly