Millennial Scale Geomagnetic and Environmental Change in the West Iberian Margin during Late Quaternary
Friday, 18 December 2015
Poster Hall (Moscone South)
Paleomagnetic and environmental magnetic studies were performed on u-channel samples collected continuously from the top ~20 to 50 m of sediments recovered during Integrated Ocean Drilling Program (IODP) Expedition 339 to the west Iberian Margin at Sites U1385, U1390, and U1391. Natural remanent magnetization (NRM) and various laboratory-induced magnetizations of the u-channel samples were measured at every 1 cm interval on a 2G Enterprises u-channel pass-through superconducting rock magnetometer, before and after a minimum of 13 step alternating field (AF) demagnetization routine at 5 or 10 mT spacing between steps, up to a maximum peak field of 100 mT. NRM demagnetization data reveal a stable and well-defined primary magnetization for samples from all three sites. Maximum angular deviation (MAD) values associated with the component direction calculations using principal component analysis (PCA) are mostly < 2°. We use a combination of radiocarbon dating, benthic and planktic oxygen isotope stratigraphy, and correlation of natural gamma radiation and X-ray fluorescence data to those of nearby well-dated piston cores, to construct reliable age models for the studied sediments. Studied samples from the three sites cover the last ~40 to over 100 kyrs, with mean sediment accumulation rates ranging from ~10 cm/kyr to over 70 cm/kyr. Occasional sandy layers in the sediments appear to correspond to significantly lower intensities of NRM and ARM, but have little influence on NRM directions. Relative paleointensity (RPI) variations at the three sites estimated using the slopes of best-fit lines of the NRM and anhysteretic remanent magnetization (ARM) data and mean NRM/ARM ratios placed on the acquired age models, show detailed (sub-) millennial scale variabilities and apparently resemble each other and RPI records from other North Atlantic regions at least on time scales of a few thousand years.