HR: 0800h
AN: GP21B-04    [Abstracts]
TI: Contributions of Sediment Provenance and Sediment Diagenesis to Western Antarctic Peninsula Magnetic Proxy Records
AU: * Brachfeld, S
EM: brachfelds@mail.montclair.edu
AF: Department of Earth and Environmental Studies, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, United States
AU: Manley, P
EM: manley@middlebury.edu
AF: Department of Geology, Middlebury College, McCardell Bicentennial Hall, Middlebury, VT 05753, United States
AU: Gorring, M
EM: gorringm@mail.montclair.edu
AF: Department of Earth and Environmental Studies, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, United States
AU: Ryan, P
EM: pryan@middlebury.edu
AF: Department of Geology, Middlebury College, McCardell Bicentennial Hall, Middlebury, VT 05753, United States
AB: We examine the role of sediment provenance, iron-sulfur diagenesis, and iron-silica diagenesis in shaping environmental magnetic proxy records in Antarctic biosiliceous sediments. A 20-m sediment core from the Gerlache Drift, western Antarctic Peninsula, contains an ultra-high resolution record of environmental change spanning the last 4000 years. Magnetic susceptibility and several remanence parameters appear to record regularly repeating patterns in biogenic and terrigenous sedimentation, with a major shift at the Middle Holocene to Late Holocene transition. This shift is manifested as an abrupt downcore decrease in magnetic susceptibility, concomitant with an increase in biogenic silica. However, this record does not show the typical pattern associated with iron-sulfur diagenesis, i.e., selective dissolution of fine particles and coarsening of the residual assemblage. We observe multidomain magnetite above the transition, and PSD-magnetite plus hematite below the transition, which suggests a change in sediment provenance. However, we observe a change in clay mineralogy downcore that is consistent with predictions for iron-silica diagenesis. In order to investigate the role of changing sediment sources vs. post-depositional diagenesis, we have examined bulk sediment geochemistry, total organic carbon and total sulfur content to identify possible diagenetic fronts, and bulk mineralogic assemblages and lithic clast composition to examine sediment sources. In addition, we have examined the lithologic and geochemical characteristics of surface sediment samples and diamict samples from a North- South suite of western AP fjords and inner shelf basins, which we use to fingerprint potential sediment source regions. These tools may be able to distinguish between sediment supplied from local Antarctic Peninsula geologic terranes, Bransfield Basin volcanics entrained in the nearshore countercurrent, or West Antarctic sediment supplied by the Antarctic Circumpolar Current.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 9310 Antarctica (4207)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly