岡山大学 地球科学研究報告
Published by Okayama University Earth Science Reports Editorial Committee

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

濱中 望 岡山大学
菅 浩伸 岡山大学
中島 洋典 有明工業高等専門学校
堀 信行 奈良大学
岡本 健裕 岡山大学
大橋 倫也 岡山大学
安達 寛 (株)ジオアクト
抄録
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.
キーワード
Holocene
coral reef terrace
drilling
sedimentary structure
Tokara Islands
northwestern Pacific
ISSN
1340-7414
NCID
AN10506284
NAID