In this paper, authors discuss on 14C data of some samples obtained from the Nakao pyroclastic flow deposits of Mt. Yakedake in the Northern Japan Alps. The samples consist of stumps, buried soil and pieces of wood or charcoal. As shown in Tab. 1 and Fig. 2, some samples obtained from the upper part of the deposits are dated older than those from the lower. It is considered that the samples which show inconsistency with stratigraphical observation have been derived from the older formation by the avalanche type of pyroclastic flow. In conclusion, the Nakao pyroclastic flow deposits are divided to three members stratigraphically, whose ages are determined after 14C dating of stumps and buried soil in situ.
A number of ancient sand dunes are developed in the plain to the southeast of Lake Mashu. The plain is also covered with thick layers of volcanic ejecta derived from the Mashu Volcano. Two layers of ancient dune sand are recognized; one is above the layer of Kamuinupuri-a volcanic ejecta and the other above the layer of Mashu-f volcanic ejecta. Very few investigations have been made about the origin of these sand dunes. After the investigations on volcanic ejecta, distribution of dunes, and mineralogical and mechanical compositions of dune sand, it is considered that the dunes consist of eolian deposits derived from channel deposits, consisting of coarse sand fraction of tephra sorted out by running water.
Paleomagnetic study was made on the Late Pleistocene Tsukabara Formation developed along the Pacific coast of Fukushima Prefecture, Northeast Honshû, Japan. The Tsukabara is the marine terrace formation which is considered to have been deposited in the Last Interglacial stage and consists of the lower gravels, the middle silts, and the upper gravels. The remanent magnetization was measured on approximately 100 oriented samples cored at about 20cm interval over the middle part of the formation at its type-locailty (37°35′N, 141°02′E). The intensity of the remanent magnetization of the sediment samples after demagnetization in the alternating magnetic field of 100 Oe ranged from 10-5 to 10-7emu/cm3. As the result of paleomagnetic analysis four horizons of polarity transition were recognized. The changes in inclination were generally associated with those in declination. Referring to the geological and biostratigraphical evidences, these reversed polarity intervals are judged to be equivalent to the Blake event (108, 000-114, 000 y.B.P.) in the Brunhes Normal Polarity Epoch, which was first reported by Smith and Foster (1969) from the North Atlantic deep-sea cores. The present result suggests a split nature of the Blake event.