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Oceanographic environment and geologic genesis of the Sekisei Coral Reef region, southern Okinawa.

冲绳南部石星珊瑚礁地区的海洋环境和地质成因。

基本信息

批准号：
60300021
负责人：
UJIIE Hiroshi
金额：
$ 4.86万
依托单位：
University of the Ryukyus
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-60300021/
关键词：
Ryukyu Island Arc Recent coral reef Sekisei-sho Sea-water composition Sediments Uni-boom survey Tilting タービダイト・エプロン

项目摘要

"Sekisei-sho" is provided with a large lagoon which is developed over the area of ca.15km (north-southly) by ca. 25km (east-westerly) between Ishigaki-jima and Iriomote-jima of the southern Ryukyu Island Arc. This is a typical Recent coral reef developed at the active ocean margin.STD survey and chemical analysis of sea water reveal a considerably homogeneity of envrionmental condition within the lagoon and also a distinct but areally restricted influence of fresh water invasion by two rivers. Various analyses of 90 sediment samples indicate that calcareous organic remains (particularly hexacorals) rule over the characters of the lagoon sediments whereas terrigeneous materials affect on those of sediments in the outside of the lagoon.The uni-boom survey suggests that the base of this Recent reef may be located around 25m in water depth with a trend slightly deepening toward the north. This northward tilting during the Holocene preiod is more clearly shown in the altitudinal deistribution and age-assignment of many emerged notchs and beach rocks in the adjacent islands. According to geological re-examination of a number of air-gun seismic profiles, the late Pleistocene reefal formation (Ryukyu Limestone) also tilts northwards in accompanying with two step faults on the northern side (i. e. Okinawa Trough side) of Sekisei-sho. On the other hand, the southern side shows a steep slope composed essentially of the pre-Pleistocene basements and some turbidite aprons are well developed at the slope base which terminates in the Sakishima Deep-sea Terrace. All of these facts indicate that the tilting movement characterizes the Holocene tectonics of this island arc region as a meaningful aspect of the Okinawa Trough spreading.

“Sekisei-sho”提供了一个大的泻湖，它是由约15 km（南北）的面积开发的。位于琉球岛弧南部的石垣岛和西表岛之间的25公里（东西向）。这是一个典型的现代珊瑚礁，发育在活动的海洋边缘，STD测量和海水化学分析表明，泻湖内的环境条件具有相当的均一性，两条河流的淡水入侵对泻湖的影响也是明显的，但在区域上是有限的。90个沉积物样品的各种分析表明，石灰质有机残留物（特别是六角珊瑚）统治的泻湖沉积物的特征，而陆源物质的影响，在泻湖的外部沉积物的uni-boom调查表明，这个现代生物礁的基础可能位于水深约25米的趋势略有加深向北。全新世时期的这种向北倾斜在邻近岛屿上许多出露的切迹和海滩岩石的海拔变化和年龄分配中表现得更为明显。根据多条气枪地震剖面的地质复查，晚更新世生物礁建造（琉球灰岩）也向北倾斜，并伴随着北方一侧的两个阶状断层（即琉球灰岩）。e.冲绳海槽一侧）。另一方面，南侧显示了一个陡坡，主要由前更新世基底组成，一些浊积岩裙在斜坡底部发育良好，终止于崎岛深海阶地。所有这些事实表明，倾斜运动的特点，全新世构造的岛弧区作为一个有意义的方面，冲绳海槽扩张。