Investigating Paleoenvironmental Influences on the Magnetic Record from the Pacific Northwest Margin since the Last Glacial Maximum

The Pacific Northwest margin is a dynamic environment that has experienced large changes since the Last Glacial Maximum (LGM). Proximal and distal glacial retreat of the Cordilleran Ice Sheet (CIS), catastrophic floods, active tectonics, regional volcanism, and variable hydroclimate and productivity all influence sedimentation and post-depositional processes on the margin, and are likely to affect the magnetic record in complex ways. We investigate how these processes influence the paleomagnetic and environmental magnetic record in three co-located sets of piston/trigger cores from the upper continental slope (~825m water depth) just south of Astoria Canyon on the Oregon margin. Preliminary correlations are supported by foraminiferal radiocarbon dates, indicating recovered sediments range in age from the LGM to the modern. We combine u-channel sediment magnetic data with physical properties, computed tomography (CT), x-ray fluorescence (XRF), and other datasets to better understand stratigraphic variations in magnetic mineral assemblages and how these properties reflect paleoenvironmental changes and influence the paleomagnetic properties of the sediments. A distinct transition in lithology and depositional structures dated to ~12ka is evident in physical properties, CT scans, and preliminary geochemistry, likely reflecting the end of ice-proximal depositional processes. Holocene sediments are texturally relatively homogenous muds, with early Holocene lamination preservation likely reflecting margin hypoxia. Late glacial sediments are characterized by greater textural and mineralogical variability, with recurrent silt-clay couplets presenting as mm-scale laminations in the late deglacial, and cm-scale structures in the early deglacial. Magnetic susceptibility is low through the Holocene, and higher during the early deglacial. Inclination trends are replicated between the cores, are comparable to other regional records, and are centered near geocentric axial dipole predictions. Measurements of anhysteretic remanent magnetization (ARM) and kARM/k, in the context of lithologic and XRF data, will assist in determining where diagenesis affects the recorded magnetic signal, changes in source and transport, and changes in environmental processes through the deglaciation.