岡山大学理学部地球科学教室 Acta Medica Okayama 1340-7414 15 1 2009 吐喝喇列島・小宝島の完新世隆起サンゴ礁段丘地形と堆積構造 33 65 EN Nozomu Hamanaka Hironobu Kan Yosuke Nakashima Nobuyuki Hori Takehiro Okamoto Tomoya Ohashi Hiroshi Adachi 10.18926/ESR/15025 Well-developed Holocene raised coral reef terraces are formed in Kodakara Island (29°13'N 129°19'E), Tokara Islands, northwestern Pacific, Japan. Detailed morphology and sedimentary structure of the raised reef terraces are observed by field survey through the terraces surface and core drillings. The Holocene raised reef in Kodakara Island are divided into three terraces (TI to III). The surface geo-biological facies and paleo-morphology such as spur and groove system or reef mounds are well preserved on these terraces. The raised coral reefs in Kodakara Island consist of reef flats and reef slopes. No lagoon formed in these terraces. On the raised reef surface, we observed five distinct reefal facies (S-f1-5). The platy and encrusting Acropora facies is the major constituent of the terrace surfaces. We obtained seven drilling cores (B1 to 7) from Terraces I and II along a transect in the southern part of the island. The thickness of the Holocene reef is more than 14m which is approximately equivalent to the Holocene reefs in the middle and southern Ryukyu Islands. Sedimentary structure consists of seven facies (C-f1-7: five reefal and two non-reefal facies). The drilling cores indicating the shallowing sequence at the upward of the cores which characterized by platy-encrusting Acropora facies overlying massive Porites, favid and/or encrusting-foliaceous coral facies. It may indicate the environmental change such as wave-energy gradients and turbidity during the reef development. No potential conflict of interest relevant to this article was reported.

岡山大学理学部地球科学教室 Acta Medica Okayama 1340-7414 11 1 2004 東アジアにおける最終氷期最盛期から完新世初期の海洋古環境 23 31 EN Hironobu Kan 10.18926/ESR/13867 A series of marginal seas that are separated from the Pacific Ocean by island arcs developed in Eastern Asia. The environmental property of these marginal seas amplified under a sea-level lowstand during the Last Glacial Maximum (LGM). The Japan Sea was covered by low salinity water during the LGM. At the beginning of the post-glacial sea-level rise, the Oyashio Current firstly flowed into the Japan Sea throught the Tsugaru Strait. The influx of the Tsushima Current started around 10,000 yBP and become vigorously after 8,000 yBP. Meanwhile, the northward migration and influx of the Kuroshio Current into East China Sea started around 10,000 yBP and strengthened after 7,500 yBP. The route alternation of the Kuroshio Current might have contributed to the establishment of the Tsushima Current and acted as a trigger for the drastic environmental changes around the merginal seas in Eastern Asia at the time of the post-glacial sea-level rise. No potential conflict of interest relevant to this article was reported.

岡山大学理学部地球科学教室 Acta Medica Okayama 1340-7414 12 1 2005 薩南諸島・馬毛島における高緯度サンゴ礁の掘削調査 49 58 EN Hironobu Kan Yosuke Nakashima Tomoya Ohashi Nozomu Hamanaka Takehiro Okamoto Tatsuo Nakai Nobuyuki Hori 10.18926/ESR/13857 Four drilling cores are observed from a high-latitude coral reef at the northwestern Mage Island (N30゜45' 40"). The thickness of the Holocene reef is around 2.5m in the reef edge and 4m in back reef. The Holocene thickness is relatively thin comparing to the modern reefs in the middle or the southern Ryukyu Islands. The reef structure Acropora facies, reworked coral rubble facies. This zonal structure conforms to the ecological coral-zonation corresponding to the wave-energy gradient. No potential conflict of interest relevant to this article was reported.