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Reconstruction of paleoseismic history in the Nankai Trough Zone by analyzing Holocene raised limestones

全新世隆起灰岩分析重建南海海槽带古地震历史

基本信息

批准号：
13680103
负责人：
MAEMOKU Hideaki
金额：
$ 1.66万
依托单位：
Hiroshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13680103/
关键词：
Nankai Earthquake Cape Muroto coseismic uplift sessile organism paleo depth of water carbonate structure limestone

项目摘要

This study aims to elucidate paleoseismic history in the Nankai Trough Zone by using Holocene raised limestones attached to coastal rocks. Sedimentological study was conducted on Holocene limestone that occurs along the coast from Cape Muroto to Meoto-iwa located about 13 km to the north of the cape. Distribution of the limestone is limited to <10 m in elevation. The limestone is up to 4.4 meter in mean diameter and less than 0.5 m in thickness, and consists mainly of fossilized sessile organisms such as annelids, bryozoans, corals, encrusting foraminifera, and coralline algae. Associated components include barnacles, ostracods, molluscs, echinoids, benthic foraminifera, peyssonneliacean algae, and non-calcareous clasts and grains. Cement is a minor component and found in a semi-closed space between coralline algal crusts and their substrates. Modal composition of limestone was determined by a point counting technique. The results show that the limestone can be classified into 6 types on the basis of predominant fossilized sessile organisms. The dominant components are : corals and coralline algae in Type I ; coralline algae in Type II ; coralline algae, annelids and barnacles in Type III ; coralline algae and annelids in Type IV ; encrusting foraminifera and encrusting bryozoans in Type V ; and molluscs in Type VI. Comparison of vertical distribution of the six types with those of modern sessile organisms indicates the highest elevation of Type I at a particular outcrop corresponds to mean low sea level (MLSL) when the limestone formed. Therefore the Holocene limestone is considered ideal for the analysis of relative sea-level changes.

本研究旨在利用近海岩石上的全新世隆起石灰岩，阐明南开海槽地区的古地震历史。对位于莫罗托角至Meoto-Iwa海岸的全新世石灰岩进行了沉积学研究，位于该海角以北约13公里处。石灰岩的分布高度限制在10米以内。石灰岩平均直径4.4米，厚度不到0.5米，主要由环节动物、苔藓虫、珊瑚、结壳有孔虫和珊瑚藻类等固着生物化石组成。相关成分包括藤壶、介形类、软体动物、棘球类、底栖有孔虫、培松藻以及非钙质碎屑和谷物。水泥是次要成分，存在于珊瑚藻壳及其基质之间的半封闭空间中。用点计数技术测定了石灰石的振型组成。结果表明，根据固着生物化石的优势，石灰岩可分为6种类型。主要成分为：第一类珊瑚和珊瑚藻类；第二类珊瑚藻类；第三类珊瑚藻类、环节动物和藤壶类；第四类珊瑚藻类和环节动物；第五类结壳有孔虫和结壳苔藓动物；第六类软体动物。因此，全新世石灰岩被认为是分析相对海平面变化的理想材料。