Abstract
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 3.2 Ma (MIS KM 5 or 3), 2.9 Ma (MIS G 17 or 15), and 1.9 Ma (MIS 59), in the 3.5-1.7 Ma interval ; (2) the altitude of the southern strait of the Japan Sea was about 50 m above the present-day sea level during 3.3-2.5 Ma ; (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 1.71-0.8 Ma interval ; (5) the intermediate water of the Japan Sea (approximately 200 m 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 520 W/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.
