HR: 1340h
AN: PP33A-1549    [Abstracts]
TI: Depositional Trends of a Glacial/Interglacial Transition from the Chilean Margin, ODP Site 1233
AU: * Fatale, M A
EM: mefatale@exchange.ursinus.edu
AF: Environmental Studies Program, Ursinus College, PO Box 1000, Collegeville, PA 19426 United States
AU: Joseph, L H
EM: Ljoseph@ursinus.edu
AF: Environmental Studies Program, Ursinus College, PO Box 1000, Collegeville, PA 19426 United States
AB: Ocean Drilling Program (ODP) Chilean Margin Site 1233 (41°0.005?S, 74°26.992?W) provides a unique opportunity to complete a detailed investigation of changes in erosion, sedimentation, and depositional current velocities throughout a glacial/interglacial transition. Comprised of 136 meters of a relatively homogenous clay and silty clay sediment with varying amounts of calcareous nannofossils and five noted ash layers, this seemingly continuous and undisturbed 70 ky record yields an amazing average linear sedimentation rate of ~200 cm/ky (or 2 cm/decade). The continuity of the record and the site_s location shoreward of the Chile Trench, at a water depth of 838 meters in a small forearc basin on the continental slope off the coast of Chile, have implied that the sediment collected at Site 1233 was likely deposited hemipelagically from fluvial discharge originating in the nearby southern Chilean mountains. Bulk magnetic susceptibility, anisotropy of magnetic susceptibility (AMS; P' and T), organic carbon content, and calcium carbonate content analyses were completed on ~90 samples (~1 sample/800 years) from Site 1233 to aid in interpretation of climatic and oceanic conditions that existed at the time of, or just prior to, sediment deposition. Similar to shipboard results, values of bulk magnetic susceptibility are relatively high for oceanic sediment, ranging between ~4 x 10^-3 and ~5 x 10^-4 SI. Magnetic fabrics (anisotropy of magnetic susceptibility), represented by P' and T values (the strength and shape of the magnetic fabric, respectively), range from ~1.005 to ~1.06 and are typically oblate. P' values peak at ~38 and ~14 ka. Throughout the core, both carbonate and organic carbon percentages remain very low (<4%). Initial magnetic fabric results, with most P' values greater than 1.01, indicate that the sediment at this site may actually have been subject to influence by oceanic currents; thus this sediment may not derive as locally as previously assumed. However, preliminary grain size results indicate a relatively fine grain size and thus possibly a low- or no- velocity current; completion of terrigenous grain size analyses will aid in the interpretation of this depositional environment. Glacial maxima noted by Lamy, et al. (Science, 2004) do not clearly correspond to either weak or strong magnetic fabrics or distinct peaks in magnetic susceptibility. Comparison of the terrigenous grain size analyses and magnetic properties with Lamy's iron and alkenone records of Site 1233 may assist in a deeper understanding of changes in erosional and depositional processes through glacial/interglacial cycles, especially if sampling intensities can be more closely matched in future work.
DE: 1512 Environmental magnetism
DE: 3022 Marine sediments: processes and transport
DE: 4863 Sedimentation (1861)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005