摘要
秦岭北麓晚二叠世石千峰组下部的平顶山砂岩段不整合覆于早、中二叠世含煤地层之上,是一套板状交错层理十分发育并以粗碎屑长石砂岩和长石石英砂岩为主的地层,以辫状河道与辫状三角洲充填沉积占优势。平顶山砂岩段呈自南向北并向东、西两侧变薄的朵状体。平顶山砂岩以含大量的新鲜的钾长石和古水流方向自南指向北和北西为特征,明显区别于下伏含煤地层中的砂岩。石千峰组砂岩与下伏煤系砂岩的厚度、古水流方向和岩石矿物成分的截然变化,表明华北石炭、二叠纪克拉通盆地南部的陆表海至晚二叠世已经完全退出华北,盆地南缘出现了新的物源隆起区,古沉积斜坡由原来的向南倾斜转变为向北倾斜。这意味着秦岭—大别构造带与华北板块南缘在此时期已经开始发生了碰撞并隆起成山。平顶山砂岩为硅质胶结,孔渗条件很差,储集油气的希望不大。
The Pingdingshan sandstone member of the Late Permian Shiqianfeng Formation in northern foothills of the Qinling Mountains, southern Henan Province overlaid uncomformitily the Early and Middle Permian coal formation of the Shihezi Group.The thickness of this sandstone member is about 120m in the Pingdingshan area and decreases northward, eastward and westward. The Pingdingshan sandstone member consists of coarse grained arkose sandstone dominately and characteristics of large scale tabular cross bedding. The thick bedded sandstones are braided channel with fining upward sequences and braided delta deposits with coarsening upward sequences,the paleo-current direction of which mainly is from the south to the north, or to the northwest, and is opposite to the paleo-current direction of the underlying sandstones of the coal measures. Plenty fresh potash feldspars with fenester twin crystal are characteristic in the arkose, whereas plagioclase is more than potash feldspar in the detritus quartz sandstones of the coal formation. The differences of the sandstone thickness, paleo-current direction and mineral constitution of sandstones between the Pingdingshan sandstone member and its underlying Permian coal measures indicate that the southward dip slope Permo-Carboniferous cratonic epicontinental sea has been finished which was caused by the uplifting of the Qinling?-Dabie Mountains, and the depositional slope dip changed into northward and northwestward. The new sediment source area occurring in the south of Pingdingshan might be implicated the collision of the North China Plate and the South China Plate. As the siliceous cement of the sandstones, the Pingdingshan sandstone could not be reservoir rocks.
出处
《现代地质》
CAS
CSCD
2003年第4期415-420,共6页
Geoscience
关键词
天然气
平顶山砂岩段
长石砂岩
辫状河
辫状三角洲
古水流方向
板块碰撞
秦岭北麓
northern foothills of Qinling Mountains
Pingdingshan sandstone member
arkose
braided channel and braided delta deposits
paleourrent direction
collision of plates
