HR: 0800h
AN: PP41A-0625    [Abstracts]
TI: Physical Properties Record of Current Flow From Magnetic Analysis of Deep-sea Sediments at the Antarctic Peninsula Pacific Margin (OPP Sites 1095, 1101)
AU: * Pares, J M
EM: jmpares@umich.edu
AF: Department of Geological Sciences, University of Michigan 2534 CCL Bldg., Ann Arbor, MI 48109
AU: Hassold, N J
EM: nhassold@umich.edu
AF: Department of Geological Sciences, University of Michigan 2534 CCL Bldg., Ann Arbor, MI 48109
AU: Rea, D K
EM: davidrea@umich.edu
AF: Department of Geological Sciences, University of Michigan 2534 CCL Bldg., Ann Arbor, MI 48109
AU: van der Pluijm, B A
EM: vdpluijm@umich.edu
AF: Department of Geological Sciences, University of Michigan 2534 CCL Bldg., Ann Arbor, MI 48109
AB: The physical properties of bottom-current flow recorded by deep-sea sediments provide valuable information about the history of oceanic currents, their strength and direction. Specifically, details on the Antarctic Circumpolar Current (ACC) would significantly increase our understanding of late Cenozoic paleoceanography, as it is thought to isolate Antarctica from the warmer waters to the north. The Anisotropy of Magnetic Susceptibility (AMS) provides a powerful gauge for sediment fabric, as it senses preferred grain orientation in sediments and sedimentary rocks. We have determined both relative speed and azimuth of bottom-current flow in drift deposit sediments recovered at ODP Sites 1095 and 1101, Antarctic Peninsula. A total of 35 cores have been measured for AMS, providing new clues on the physical record of the ACC in the Plio-Pleistocene. Because ODP holes are drilled and recovered in successive 9 meters-long cores, which usually do not have relative orientation, we have based our analysis on samples grouped by cores. Our results indicate that the degree of anisotropy provides a proxy for current strength: The higher the latter, the higher is the anisotropy of the magnetic ellipsoid. Further, grouping of the principal axes of maximum susceptibility is interpreted in terms of preferred grain orientation, providing a proxy for the azimuth of the paleocurrent flow. As revealed by experimental studies, AMS maximum axes are grouped in the azimuth of flow and inclined at a few degrees to the sediment surface dipping downward into the direction of the flow's origin. In the studied samples, when imbrication is observed, we have been able to determine the orientation and sense of the paleocurent. Declination and inclination of the paleomagnetic vector of each core segment was used for reorientation of AMS principal axes to the geographic coordinates to obtain the absolute orientation of the directional data. Once the cores have been reoriented using the measured direction of the Characteristic Remanent Magnetization (ChRM) with respect to a common reference line for the core, we have determined the orientation of the paleocurrent flows for sites 1095 and 1101 relative to the geographic coordinates. Sites 1095 and 1101 have paleocurrent directions oriented N-S and NW-SE respectively, which in both cases are slope-parallel. Whereas both sites produce different paleocurrent directions, no significant downcore variations on the azimuth have been observed. This study shows that a combination of magnetic fabric analysis and paleomagnetism allows deep-sea sedimentary fabric to be used as a long-term proxy for bottom-current flow history.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1520 Magnetostratigraphy
DE: 4219 Continental shelf and slope processes (3002)
DE: 4512 Currents
DE: 4532 General circulation (1218, 1222)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005