[SEM20-P04] 統合国際深海掘削計画 Sites U1409 および U1410 の磁気層序の更新
The Integrated Ocean Drilling Program (IODP) Expedition 342 recovered ~5.4 km of hemipelagic sediment drifts from the Northwest Atlantic. Routine onboard measurements resulted in shipbaord magneto- and biostratigraphic age models (Norris et al., 2014). The shipboard magnetostratigraphies were based on the measurement of natural remanent magnetization (NRM) of the split-half cores after 20 mT alternating field (AF) demagnetization. In the present study, we performed detailed shore-based paleomagnetic measurements on the sedimentary sections recovered at Sites U1409 and U1410 to improve the shipboard magnetostratigraphies.
U-channel samples (typically 1.5 m in length with a 2 × 2 cm cross-section) were taken from the central part of the split half cores along the stratigraphic splice described in Norris et al. (2014): 6-142 mcd (meter composite depth) for U1409 and 0-165 mcd for U1410. We conducted progressive AF demagnetizations on NRMs of the samples up to 80 mT in approximately 10-12 treatment steps with remanence measurements at each AF step with a stratigraphic resolution of 1 cm. Characteristic remanent magnetization (ChRM) directions of the samples were typically resolved after AF demagnetization of 20-40 mT. The maximum angle of deviation (MAD) was less than 10° for most intervals of the samples.
The results show that intervals with negative inclinations are more manifested in shore-based results than they are in the shipboard results. It allowed us to locate chron boundary depths more precisely than those determined shipboard. In most cases the depths determined in the present study are not much different from those determined shipboard (less than ~1 m), but there are some boundaries which resulted in large differences. We could locate also some of new boundaries which had not been identified shipboard.
U-channel samples (typically 1.5 m in length with a 2 × 2 cm cross-section) were taken from the central part of the split half cores along the stratigraphic splice described in Norris et al. (2014): 6-142 mcd (meter composite depth) for U1409 and 0-165 mcd for U1410. We conducted progressive AF demagnetizations on NRMs of the samples up to 80 mT in approximately 10-12 treatment steps with remanence measurements at each AF step with a stratigraphic resolution of 1 cm. Characteristic remanent magnetization (ChRM) directions of the samples were typically resolved after AF demagnetization of 20-40 mT. The maximum angle of deviation (MAD) was less than 10° for most intervals of the samples.
The results show that intervals with negative inclinations are more manifested in shore-based results than they are in the shipboard results. It allowed us to locate chron boundary depths more precisely than those determined shipboard. In most cases the depths determined in the present study are not much different from those determined shipboard (less than ~1 m), but there are some boundaries which resulted in large differences. We could locate also some of new boundaries which had not been identified shipboard.