The upper reaches of the Yangtze River flowing through southern China are called Jinshajiang. Near Shangri-La City in Yunnan Province, the river flows down a narrow valley consisting of schists with a relative height of more than 3,000 m and a width of less than 100 m. The valley is called Tiger Leaping Gorge because even on a clear day the muddy water flowing down through the narrow section looks like leaping tigers. Visitors can see the muddy torrent close up as they walk down along the valley wall from the parking lot to the river side.

(Photograph & Explanation: Junko KOMATSUBARA; October 16, 2018)

 In 1995, Japan launched a national project to assess methane hydrates as future gas resources, which successfully identified and recovered hydrate-cemented sandy sediments from Pleistocene turbidite units at the Nankai Trough. Extensive geological and geophysical exploration over 20 years reveals a wide distribution of hydrate-induced BSR at the eastern Nankai Trough. The amounts of hydrates in sandy sediments are estimated to be 17 to 39 vol.% based on low salinity anomalies of squeezed pore waters. Hydrate amounts equivalent to 6 to 7 vol.% of sediment volume extend from the seafloor to the base of gas hydrate stability (BGHS). A probabilistic approach to assess amounts of hydrates based on 2D/3D seismic profiles, LWD geophysical parameters, and geochemical analysis of cores provides an approximation of the amounts of resources in place at 40 tcf of methane gas in the entire BSR area (4,687 km²) and at 20 tcf in the hydrate concentrated zone (767 km²) of the eastern Nankai Trough. An integrated academic, industrial, and national program carried out since 2004 identifies another type of hydrate in the eastern margin of the Sea of Japan. Japan Sea hydrates occur as massive aggregates in a chimney-like acoustic blanking zone of a few 100 m across and 100-120 m thick (gas chimney) in Pleistocene hemipelagic sediments. MBES and SBP surveys confirm 1,742 gas chimneys along the eastern margin of the Sea of Japan and around Hokkaido Island. Amounts of hydrates estimated from combined elastic wave velocity Vp and low salinity anomalies are 35 to 74 vol.% of the volume of the gas chimney structure. BSRs in hydrate-bearing gas chimneys exhibit a sharp pull-up structure within the gas chimneys, reflecting high Vp. Assuming that the Vp of massive hydrate is 3.7 km/sec and Vp of the host sediments in gas chimneys is same as Vp of the sediments around gas chimneys, the amounts of hydrates in the gas chimneys are calculated to be 15 to 65 vol.% of chimney volume. High Vp anomalies of hydrate-bearing sediments is also applied to hydrates estimate at the Nankai trough.

 Although temporal inconsistency in vertical deformation between long-term (> 10³ years) uplift and short-term (10¹-10² years) subsidence along the Pacific coast of northeast Japan has been discussed in relation to cycles of megathrust earthquakes by some researchers, the fragmentary distribution of Pleistocene marine terraces and sparsity of studies on Holocene coastal geology indicate a lack of data on long-term vertical deformation at the occurrence of the 2011 Tohoku-oki earthquake. Recent geological studies along the northern Pacific coast (Sanriku coast), which were conducted after the 2011 earthquake, contribute to considerations of temporal inconsistency by providing new data on long-term vertical deformation. However, such studies have not been completed for the southern part of the coast. Millennial-scale vertical deformation at the Mano River Lowland, on the southern Pacific coast of northeast Japan is studied on the basis of well-dated Holocene sediment cores and existing boring logs. Subsurface geology documents the transgression and regression of the back-barrier estuary in the wave-dominated estuary system during the Holocene. The low relative sea-level (RSL) in the Early and Middle Holocene inferred from heights of marsh and intertidal sediments relative to non-tectonic hydro-isostatic sea-level predictions indicates a millennial-scale trend of subsidence at the Mano River Lowland. However, RSL in the Middle Holocene at the study area estimated from the sedimentary environment at that time is higher than that in the Tsugaruishi plain, northern Pacific coast of northeast Japan, where a millennial-scale subsidence of 1.1-1.9 mm/yr was previously inferred. This indicates that the Mano River lowland has been uplifted relative to the Tsugaruishi plain on a millennial scale. In combination with the deformation trend inferred from the distribution of the MIS 5.5 marine terrace, a change in the vertical deformation trend from stable or slight uplift to slight subsidence is implied to occur in the Mano River Lowland sometime between Late Pleistocene and Early Holocene.

 The Hida belt in central Japan represents a unique geotectonic unit of non-subduction-related origin, in sharp contrast with the rest of the Phanerozoic crust in Japan. Its origin and relative geotectonic position with respect to surrounding continental blocks in East Asia, such as Greater South China (GSC), North China, and Siberia, remain unresolved. To confirm the geologic/orogenic identity of the Hida belt, the geochronology of detrital zircons is analyzed for seven non-marine sandstones of the Lower Cretaceous Tetori Group. New age data confirmed that all analyzed sandstones probably belong to Lower Cretaceous (Barremian to Aptian), regardless of areas within the belt. The trace element composition of detrital zircons indicates their derivation mostly from I-type granitoids, and in part from A-type granite. Late Triassic granitoids are extremely rare in the present Hida belt, and A-type granite is absent; nonetheless, the present data, together with large boulders in conglomerate, indicate extensive exposure of such granitoids in the Early Cretaceous provenance of the Tetori sedimentary basin. It is noteworthy that Late Triassic A-type granites occur solely in NE China within Far East Asia; thus an intimate link between the Hida belt and the Laoelin–Grodekov (LG) belt in the Russia/China/N. Korea border domain is suggested. As Tetori sandstones have a remarkable contrast in zircon age spectra with the coeval sandstones deposited in shallow marine fore-arc basins in Japan, the Tetori Group was deposited probably in the periphery of a large-scale inland non-marine basin in Cretaceous NE Asia, which was located particularly at the back-arc side of the active volcanic arc.

 After World War II, geochemistry in Japan began with research on hot springs. During the post-war occupation period, research in the field of atomic energy was prohibited and exchanges with foreign countries were restricted. Consequently, hot springs research was thought to be a unique area of research that could be conducted in Japan. Postwar geochemistry research in Western countries, particularly in the United States, focused on trace elements, radioactive isotopes, and stable isotopes. Such research required high-precision analysis equipment. Japanese researchers who lacked the necessary research environment were then able to travel abroad. They began to conduct research in the United States and bring the results back to Japan. Thus, geochemical studies in Japan progressed. The intellectual stimulation researchers experienced abroad was also significant. The history of geochemistry in Japan from 1945 to 1965 is described, covering ten topics: hot spring chemistry, radiometric dating, the works of Akimasa Masuda and rare earth chemistry, stable isotope geochemistry, cosmochemistry, the works of Paul Kazuo Kuroda and nuclear chemistry, Antarctic science, sociogeochemistry (social geochemistry), textbooks published in Japan, and societies and laboratories newly established during this period.