Magnetic observation of ODP Site 152-919 in the Irminger Basin, North Atlantic

Component natural remanent magnetizations derived from u-channel and 1-qcm discrete samples from ODP Site 919 (Irminger Basin) indicate the existence of four intervals of negative inclinations in the upper Brunhes Chronozone. According to the age model based on planktic oxygen isotope data, these "excursional" intervals occur in sediments deposited during the following time intervals: 32-34 ka, 39-41 ka, 180-188 ka and 205-225 ka. These time intervals correspond to polarity excursions detected elsewhere, known as Mono Lake, Laschamp, Iceland Basin and Pringle Falls. The isotope-based age model is supported by the normalized remanence (paleointensity) record that can be correlated to other calibrated paleointensity records for the 0-500 ka interval, such as that from ODP Site 983. For the intervals associated with the Mono Lake and Laschamp excursions, virtual geomagnetic poles (VGPs) reach equatorial latitudes and mid-southerly latitudes, respectively. For intervals associated with the Iceland Basin and Pringle Falls excursions, repeated excursions of VGPs to high southerly latitudes indicate rapid directional swings rather than a single short-lived polarity reversal. The directional instability associated with polarity excursions is not often recorded, probably due to smoothing of the sedimentary record by the process of detrital remanence (DRM) acquisition.

K-Ag age of volcanites from underwater rises of the Sea of Okhotsk and the Sea of Japan

New K-Ar datings of Meso-Cenozoic volcanites from the Sea of Japan and the Sea of Okhotsk were obtained. They enabled to reason age of different volcanic complexes. Basalts from volcanic edifices of the Sea of Japan Basin were determined as Middle Miocene - Pliocene (13.1-4.5 Ma) in age, which correlates well with geological evolution of the Sea of Japan. New datings for basalts from the continental slope of the South Primorye (11.1 Ma) confirm their age being similar to volcanites from Neogene basalt plateaus of the South Primorye; they are very similar not only in age but also in mineral and chemical compositions. Datings for rocks from the andesite series of the Northern Yamato Rise (24.7, 21.5 Ma) show that they are coeval with volcanites of the trachyandesite complex; this allows to combine them into one Oligocene - Early Miocene complex. In the Sea of Okhotsk datings of volcanite samples from three complexes were obtained: Cretaceous, Paleogene, and Pliocene-Pleistocene. Cretaceous magmatic rocks make part of basements of large rises in the Sea of Okhotsk, and Paleogene and Pliocene - Pleistocene complexes illustrate stages of Cenozoic tectono-magmatic activation of the region.