Change of marine environment based on analysis of Early-middle Triassic radiolarians

基于早中三叠世放射虫分析的海洋环境变化

基本信息

批准号：
07640625
负责人：
YAO Akira
金额：
$ 0.26万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640625/
关键词：
Lower-Middle Triassic radiolarian fossil assmblage marine environment siliceous claystone bedded chert

项目摘要

This study aimed to reconstruct the Early-Middle Triassic marine environment of the Panthalassa region on the basis of radiolarian research. Firstly, field work and rock sampling were carried out in the continuous stratigraphic sections of the lower to Middle Triassic siliceous sequence of the Mino Terrane, central Japan. Secondly, the faunal composition of the Early-Middle Triassic radiolarian assemblages was examined and compared with the Late Permain and Jurassic radiolarian assemblages, and petrographical features of siliceous rocks were described.The lower Triassic is mainly composed of siliceous claystone with thin black mudstone layrs in which radiolarian remains are rare and their variety is very low. The Middle Triassic mainly consists of red bedded chert sequence in which Mesozoic type radiolarians are abundantly contained and their variety becomes higher upward. The lower Triassic siliceous claystone gradually changes to the Middle Triassic bedded chert.On the other hand, the Upper Permian of the Mino Terrane excluding carbonate facies is represented by bedded chert sequence in which the highly varied Paleozoic type radiolarians are contained.On the basis of above mentioned results, it is considered that the marine environment of the low-latitudinal Panthalassa region during Early Triassic time was affected by the worldwide anoxic event, and that no bedded chert of the Lower Triassic depended on the low productivity of radiolarians. The lithologic change from the Early Triassic siliceous claystone to the Middle Triassic bedded chert shows that the high productivity of radiolarians recovered during Middle Triassic time. The Middle Triassic red bedded chert is considered to be formed under the oxic environment. It is concluded that the large scaled faunal change of radiolarians through Late Permian to Middle Triassic time was controlled by the marine environmental change.

本研究旨在以放射虫研究为基础，重建Panthalassa地区早-中三叠世海洋环境。首先，在日本中部美浓地体下三叠世至中三叠世硅质层序的连续地层剖面中进行了野外工作和岩石取样。其次，考察了早中三叠世放射虫组合的动物组成，并与晚二叠世和侏罗世放射虫组合进行了比较，描述了硅质岩的岩石学特征。下三叠统主要由硅质粘土岩组成，夹有薄层黑色泥岩层。其中放射虫遗骸非常罕见，而且种类也很少。中三叠世主要为红层燧石层序，中生代类型放射虫发育丰富，且种类向上变高。下三叠统硅质粘土岩逐渐转变为中三叠统层状燧石。另一方面，米诺地体上二叠统不包括碳酸盐相，以层状燧石层序为代表，其中含有高度变化的古生代型放射虫。上述结果认为，早三叠世低纬度Panthalassa地区的海洋环境受到了世界性缺氧事件的影响，下三叠统的层状燧石不依赖于放射虫的低生产力。从早三叠世硅质粘土岩到中三叠世层状燧石的岩性变化表明，中三叠世放射虫的高生产力得到了恢复。中三叠世红层燧石被认为是在有氧环境下形成的。结论是晚二叠世至中三叠世期间放射虫动物区系的大规模变化是受海洋环境变化控制的。