High-resolution paleomagnetic secular variation for the last 20 kyr from varved sediments of Fukui-SG14 core from Lake Suigetsu, central Japan

Paleomagnetic secular variation (PSV) for the last 20 kyr was investigated using the varved sediments from Lake Suigetsu, central Japan. Notable merits of this study include relatively high accumulation rate of the sediment (99 cm/kyr in average for the last 20 kyr) and the exceptionally high precision of the chronology, for example ± 61 yr for 20 kyr BP. which was established by a combination of varve count data and over 800 14C determinations. Perfectly continuous set of cores, named Fukui-SG14, was collected by the Fukui prefectural government in 2014. A total of 274 overlapping core sections of up to 1m length were obtained from four nearby bore holes. For magnetic analyses, we subsampled 38 double-L channel sections, 16 of which are magnetically oriented, and 16 cubes from the cores. Progressive alternating field demagnetizations (AFD) and thermal demagnetizations (THD) revealed that natural remanent magnetizations (NRM) usually decay toward the origin above 20-30 mT and 300 °C, respectively, at which a viscous remanent magnetization (VRM) is completely removed. THD results and thermal changes of magnetic susceptibility suggest that the magnetic carriers are magnetite, titanomagnetite, and a ferrimagnetic iron sulfide mineral (greigite), and that the iron sulfide component is not negligible in weak intensity NRMs, whose AFD results show a magnetic vector which does not decay toward the origin. A half of specimens subjected to THD, which have strong intensity NRMs, provide a characteristic remanent magnetization (ChRM) consistent with that isolated by AFD. Remanent magnetizations of double-L channel samples were measured every 1cm interval, being subjected to AFD of up to 80mT. A ChRM was isolated from strong intensity NRMs by the principal component analysis. We have so far obtained 511 ChRMs that provide a PSV curve of inclination and declination for the last 20 kyr, which can be used as a regional reference. For the Holocene interval, the present PSV data show features quite consistent with several PSV curves from East Asia. The comparison of PSV data enables us to transfer the precise SG06 chronology to other regions in East Asia.