In this study, we analyzed the carbonized residue adhering to the inner surface of pottery excavated at the Hyakunincho 3-chome Nishi site, Tokyo, Japan. We examined the chronological position of the linear relief pottery group at the beginning of the Incipient Jomon period, which is the earliest pottery stage in the history of the Japanese archipelago. A small amount of carbonized residue was found adhering to the pottery. Radiocarbon dating using micro sample analysis was performed on the residue, dating the pottery to 15,270-14,940calBP. Furthermore, carbon and nitrogen stable isotope analyses showed that the carbonized residue originated from terrestrial flora and fauna and indicated that the dating results were highly reliable. The radiocarbon dating results for 50 samples of carbonized residue found in linear-relief pottery were compared with the early stage linear-relief pottery excavated from Layer 3c of Fukui Cave in Nagasaki Prefecture. Linear-relief pottery was made for approximately 2000 years beginning about 16,000 years ago. The pottery found at the Hyakunincho 3-chome Nishi site dates within the middle stage among them.
The detailed investigation of stratigraphic distribution of molluscan shells and planktonic foraminifera in the Lower Pleistocene Omma Formation in Kanazawa, Ishikawa Prefecture, Japan, provided the following conclusions : (1) the Tsushima Current flowed into the Japan Sea at 3.2Ma (MIS KM 5 or 3), 2.9Ma (MIS G 17 or 15), and 1.9Ma (MIS 59), in the 3.5-1.7Ma interval ; (2) the altitude of the southern strait of the Japan Sea was about 50m above the present-day sea level during 3.3-2.5Ma ; (3) the early formation of strait was located at southwest of Cheju Island ; (4) the current flowed at every interglacial highstand, except for MIS 25, 23, and 21.3, in the 1.71-0.8Ma interval ; (5) the intermediate water of the Japan Sea (approximately 200m depth) at MIS 47, 45, 43, 41, and 29 was the warmest in the Quaternary, and was gradually followed by coldness. In addition, the stratigraphic data indicated that during the interglacial period, when the average monthly July insolation was greater than 520W/m2 at 65°N latitude, a significant decrease in molluscan species diversity and abundance occurred along the coast of the Sea of Japan in Honshu, Japan. It is highly likely that this temporal condition was caused by an increase in seasonal differences caused by a faster rise in summer temperatures than winter temperatures.
The Great East Japan Earthquake of 2011 triggered my research on paleo-tsunami and paleo-earthquakes in Shizuoka Prefecture. The main results of the research are as follow : (1) the appearance of a tsunami boulder, which was associated with the 1854 Ansei-Tokai earthquake, on a wave-cut bench at Shimoda, Shizuoka ; (2) the emergence of boring bivalves at Cape Omaezaki, Shizuoka, Japan, which are evidence for coseismic uplift during the 1361 Shohei (Koan) earthquake ; (3) the occurrence of a submarine landslide caused by the 1096 Eicho-Tokai earthquake in the Hamatome lowlands of Yaizu ; (4) geologic evidence for coseismic uplift at ～AD 400 in coastal lowland deposits on the Shimizu Plain ; (5) no geologic evidence of the largest-possible tsunamis (Level 2) having occurred in the coastal area of Shizuoka Prefecture during the past 4000 years, meaning that an extreme Level 2 event will not occur at the time of the next Nankai Trough earthquake.
Feldspar optically stimulated luminescence (OSL) dating was applied to the channel sediment in an abandoned river valley around a cutoff spur formed by the Totsukawa River in the Kii Mountains, southwestern Japan. The depositional age of the channel sediment was not determined because the dated feldspar grains were likely to be incompletely bleached to various degrees, and most of the grains attained saturation in OSL signals. However, the depositional age was constrained to be younger than 280 ka based on the characteristic saturation dose of the dose response curve measured from “unsaturated” feldspar grains. The river-incision rate calculated from the constrained depositional age was consistent with the denudation rates estimated from sediment yields in catchments. This result indicates that, even if the determining depositional age of the sediment is difficult due to the insufficient bleaching, constraining that age may be possible by using the characteristic saturation dose of the dose response curve measured from unsaturated feldspar grains.