Late Pleistocene and Holocene Paleomagnetic Records from the Gulf of Alaska: Preliminary Results of IODP Expedition 341 Sites U1418 and U1419

English Abstract:

During IODP Expedition 341 in the Gulf of Alaska, Sites U1418 and U1419 were drilled in the upper part of the Surveyor Fan and on the continental shelf edge, respectively. These Sites recovered exceptionally expanded records containing information on climatic, oceanographic, glacial, tectonic and geomagnetic field changes in the eastern North Pacific region over at least the last 60 kyr. As a first step in evaluating the potential of the sediments of Sites U1418 and U1419 to record a reliable relative paleointensity (RPI) signal, the shipboard natural remanent magnetization (NRM) at 20 mT was normalized by magnetic susceptibility and compared with the shipboard inclination record. At Site U1419, two intervals of low normalized intensity and reversed inclination were recovered with preliminary ages consistent with the Laschamp and Norwegian-Greenland Sea geomagnetic excursions at ~ 41 and ~ 61 ka, respectively. U-channel and discrete sample studies to verify these observations are ongoing. A first series of u-channels from Site U1418 were analyzed using stepwise alternating field demagnetization to further clarify the shipboard paleomagnetic observations. These data indicate that a strong, well-defined, single component magnetization with maximum angular deviation (MAD) values generally lower than 5^o is preserved. Moreover, alternating gradient force magnetometer analyses at Site U1418 imply that the sediments at the Site consist mainly of low coercivity minerals in the pseudo-single domain range. These preliminary results indicate that the Gulf of Alaska sediments preserve a promising high-resolution paleo-geomagnetic record. The shipboard data will be complimented by more detailed u-channel studies in order to establish a stratigraphic framework and investigate geomagnetic field dynamics during the Late Pleistocene and Holocene.