贵州贵阳地区下三叠统沙堡湾组遗迹化石的发现及其意义

The Discovery of Trace Fossils from the Lower Triassic Shabaowan Formation in the Guiyang Region,Guizhou and Their Significance

摘要:

贵州区域地质调查大队一分队在作贵阳片区1:50000区调过程中,首次发现该区(图1)下三叠统沙堡湾组上部灰岩中有大量丰富的生物潜穴化石存在。本文在介绍该组遗迹化石的基础上,根据遗迹化石特征和其它沉积标志对黄铁矿是否一定指示沉积底层水体为还原环境和遗迹化石组合是否绝对受海水深度控制提出看法。

Abstract:

The abundant trace fossils are of widespread occurrence in the upper part of the Lower Shabaowan Formation in the Guiyang area, including four genera: Arenicolites. Psilonichnus, Skolithas and Thalassinoides. In addition. the Y-shaped burrows have also been identified in the formation, indicating that biologic activity may be traced in the course of deposition of the formation and that the water body in which the bottom beds were deposited may not be in a reducing environment. Occasionally, a small amount of pyrite are scattered in the limestones which contain the trace fossils, but this doesn＇t mean that the environments of the sedimentary rock beds which comprise a small amount of pyrite may be ascribed to the reducing ones. In fact, pyrite may result from diagenetic processes.
The“shallow-water”trace fossils—intraformational burrows have been recognized in the Shabaowan Formation which is ascribed to the shallow-sea shelf sediments. It follows that the trace fossil assemblages are not absolutely controlled by water depth, because the characteristics of the trace fossils are dependent not only upon water depth, but also upon bottom bed types, energy levels, food suply, preservation potential and the habits and characteristics of the organisms.