甘肃文县上震旦统重力流沉积及其构造古地理的意义

分布于甘肃文县一带的原“碧口群”据岩性、层位特征及微古植物化石厘定为震旦系,并可进一步划分出南沱组、陡山沱组、灯影组。在陡山沱组发育一套陆源浊积岩和深水相泥质岩、硅质岩组合,底部夹有多层火山碎屑岩及火山熔岩;灯影组发育碳酸盐岩浊积岩层和重力滑动层。这些浊积岩能够在地质记录中得以保存且厚度可达数百米,说明该区当时受到一个相对活动的从深水海沟演化到较浅水弧后盆地这一沉积构造环境的控制,从而说明扬子地台北缘应是具有拉张活动性质的被动大陆边缘。

WITHIN THE LATER SINIAN SERIES, THE GRAVITY CURRENT DEPOSITS AND ITS TECTONIC PALEOGEOGRAPHIC SIGNIFICANCE IN WENXIAN OF GANSU

The " Bikou group" that distributed in Wenxian county of Gansu, on the basis of the features of lithology and sequence and micropaleoflora, should be named the Sinian. It may be divided into three formations : Nantuo formation, Doushantuo formation and Dengying formation. The Doushantuo formation consisted of continental turbidite and deepwater pelite and silicalite,and at lower part of this formation , there are partings of pyroclastic rock and lava; The Dengying formation encluded carbonate turbidite and gravity sliding layer. In so long geological history,these turbidites can be preserred and have hundreds of meters thick. At that time,it shows this area was controlled by the sedimentary tectonic setting which e-volved from deep trench to shallow back arc basin and indicated that the north edge of Yangtze platform must be the pulling-apart edge of the passive continent.