JaLCDOI 10.18926/ESR/15025
Title Alternative Morphology and Anatomy of Holocene Raised Coral Reef Terraces in Kodakara Island, Tokara Islands, northwestern Pacific, Japan
FullText URL 015_033_065.pdf
Author Hamanaka, Nozomu| Kan, Hironobu| Nakashima, Yosuke| Hori, Nobuyuki| Okamoto, Takehiro| Ohashi, Tomoya| Adachi, Hiroshi|
Abstract 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.
Keywords Holocene coral reef terrace drilling sedimentary structure Tokara Islands northwestern Pacific
Publication Title Okayama University Earth Science Report
Published Date 2009-03-31
Volume volume15
Issue issue1
Start Page 33
End Page 65
ISSN 1340-7414
language 日本語
Copyright Holders 岡山大学地球科学研究報告編集委員会
File Version publisher
NAID 120002308005
JaLCDOI 10.18926/ESR/13857
Title Alternative Drilling Research of a high-latiude coral reef in Mage Island, Stsunan Islands, Japan
FullText URL ESR_12_49.pdf
Author Kan, Hironobu| Nakashima, Yosuke| Ohashi, Tomoya| Hamanaka, Nozomu| Okamoto, Takehiro| Nakai, Tatsuo| Hori, Nobuyuki|
Abstract 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.
Keywords Holocene Coral Reef Sedimentary Structure Drilling Southwestem Japan
Publication Title Okayama University Earth Science Report
Published Date 2005-12-31
Volume volume12
Issue issue1
Start Page 49
End Page 58
ISSN 1340-7414
language 日本語
Copyright Holders 岡山大学地球科学研究報告編集委員会
File Version publisher
NAID 120002310535
JaLCDOI 10.18926/ESR/13867
Title Alternative Paleoceanography of the Eastern Asia from the Last Glacial Maximum to the early Holocene
FullText URL earth_science_reports_011_1_23.pdf
Author Kan, Hironobu|
Abstract 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.
Keywords Paleoceanography Last Glacial Maximum
Publication Title Okayama University Earth Science Report
Published Date 2004-12-31
Volume volume11
Issue issue1
Start Page 23
End Page 31
ISSN 1340-7414
language 日本語
Copyright Holders 岡山大学地球科学研究報告編集委員会
File Version publisher
NAID 120002310301