HR: 0830h
AN: PP31B-0263    [PDF]
TI: Environmental magnetism of late Cenozoic sediments from the East Antarctic continental rise (Site 1165, Prydz Bay)
AU: * Richter, C
EM: richter@louisiana.edu
AF: Department of Geology University of Louisiana at Lafayette, PO Box 44530, Lafayette, LA 70504 United States
AU: Warnke, D
EM: dwarnke@csuhayward.edu
AF: California State University, 25800 Carlos Bee Boulevard, Hayward, CA 94542 United States
AU: Florindo, F
EM: florindo@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AB: The objective of this study is to advance our understanding of the late Cenozoic environmental history of East Antarctica as part of a multiparameter interdisciplinary project. We analyzed a set of 500 samples taken at 10 k.y. resolution from the Plio-Pleistocene section at Ocean Drilling Program Site 1165. The site is located on Wild Drift, a thick contourite deposit on the continental rise off Prydz Bay, East Antarctica. The data set provides a 5 m.y.-old record of environmental change and ice-sheet history with the opportunity to link the histories of the Antarctic Ice sheet and the distal ocean-current and climate systems. As part of this project we investigated the sources of magnetic remanence and magnetic susceptibility variations by characterizing rock magnetic properties. Variations in grain size, mineralogy, and concentration of magnetic grains reflect pre- and post depositional environmental changes, yielding clues to fluctuations in climate, source material, and depositional environments. From the beginning of the record at about 5 Ma throughout the early Pliocene the concentration of magnetic material varies very little, while the magnetic mineralogy and the magnetic grain size (S-ratio, and ARM/k and ARM/IRM ratios) shows various large and small scale cycles. A remarkable change occurs at 34 mbsf in the lowermost, normal interval of the Gauss Chron, at about 3.4 Ma(?), where the magnetic grain size increases dramatically. This significant change is expressed in non-magnetic measurements as well, and may coincide with the beginning of ice rafting in the South Atlantic during MIS MG2, just above an interval without any IRD (Murphy et al., 2002). Another significant change in the magnetic properties occurs at 30-28.5 mbsf (around 3.3 Ma) where the magnetic concentrations drop to very low values and the magnetic properties are carried by a high-coercivity component. These changes may reflect climate variations or changes in the location of the source area within the Lambert-Graben drainage area.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting