HR: 15:10h
AN: GP33E-07    [Abstracts]
TI: Observations on the Sediment Magnetic Acquisition Process from Multicores Collected From the SE Alaska Margin
AU: * Stoner, J S
EM: jstoner@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331, United States
AU: Rosen, G P
EM: rosengp@ufl.edu
AF: University of Florida, Department of Geological Sciences, Gainesville, FL 32611, United States
AU: Jaeger, J M
EM: jaeger@geology.ufl.edu
AF: University of Florida, Department of Geological Sciences, Gainesville, FL 32611, United States
AU: Channell, J E
EM: jetc@geology.ufl.edu
AF: University of Florida, Department of Geological Sciences, Gainesville, FL 32611, United States
AB: Understanding of the magnetic acquisition processes of marine sediments has been hindered by a lack of fundamental observation from natural settings. Here we present new paleomagnetic observations from a variety of sedimentary environments that characterize the SE Alaska Margin. Twenty-five multicores collected during the R/V Ewing cruise EW0408 were studied. These sites range from biogenically dominated, organic carbon-rich sediments from coastal environments along the Alaska Panhandle to glacimarine and paraglacial coastal and open marine settings with high rates of terrigenous sediment accumulation. Paleomagnetic and environmental magnetic records were studied by progressive AF demagnetization of u-channel samples emplaced in split multicores that were sub-sampled around the u-channel to prevent deformation. The sediments were characterized using x-radiography, physical grain-size, density, organic carbon and biogenic silica analyses. Biogenic mixing rates and depths were determined by excess Th-234 (t1/2=24 d) verified with x-radiographs and accumulation rates were established by Pb-210 constrained by bomb-derived Cs-137 activity. Initial age models were developed and used to compare the component magnetizations with Jackson's historical field model locally constrained by the Sitka Geomagnetic Observatory. In general, there is a strong, significant correlation between the organic carbon and biogenic silica concentrations and biological mixing parameters, indicating that bioturbation intensity and depth is determined by the labile carbon flux. There is an inverse correlation between bioturbation intensity and the NRM efficiency, measured by the normalized remanence values, and quality, measured by comparisons with historical data and PCA analysis of the demagnetization data. Depth to lock-in, as determined by inclinations reaching historically consistent values of approximately 70° and stability of the normalized remanence values, varies widely and is also generally a function of the organic carbon content. In terrigenous-rich, low biogenic environments the magnetization lock-in zone is generally less than 10-cm and in some cases too thin to be detectable. In the biogenically dominated environments, lock-in occurs substantially later, implying that the thickness of the lock-in zone is a function of the thickness of the bioturbated layer.
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
DE: 3022 Marine sediments: processes and transport
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting