黔北桐梓奥陶系五峰组黑色页岩的笔石定向性

The Orientations of Graptolite Fossils from the Ordovician Wufeng Formation Black Shale in Tongzi,North Guizhou,China

黔北桐梓奥陶系五峰组黑色页岩中产有丰富的笔石,对这些笔石和其碎片的长轴在水平投影方向进行测量,结果表明笔石具有定向排列的特征。同时,从黑色页岩段Dicellograptus com-plexus带至观音桥段Normalograptus extraordinarius-Normalograptus ojsuensis带笔石的排列方向呈现由NE-SW至N-S再至NW-SE的逐渐变化,且其定向排列的方向性逐渐明显。五峰组黑色页岩中笔石定向性排列的特征可以解释为其沉积环境中存在一定的水动力条件,而剖面纵向上笔石定向性的变化可能与奥陶纪末期加里东运动导致滇黔桂古陆海岸线的变化有关。

The results, which measure the long-axis of graptolite fossils and fragme show that the graptolites from the black shale of the Ordovician Wufeng Formation ty, the orientations of graptolite fossils and fragments, from the D. complexus zone to the N. extraordinarius-N, ojsuensis zone of NW-SE; and their directionality is enhanced nts projection on the horizon, bear an orientational regulari- of the Wufeng Shale Member the Guanyinqiao Member, appear a change from NE-SW to N-S to gradually. The characteristics of the graptolite orientation show that the black shale of the Wengfen Formation deposited in an energy-low environment. In addition, the changing regularity of the graptolite orientation on section maybe relate to the coastline changes of Yunnan-Guizhou-Guangxi Old Land resulted from Caledonian movement in the Late Ordovician.