延长油田东区下二叠统山西组物源分析

Provenance Analysis of Shanxi Formation in Lower Permian Series in East Yanchang Oilfield

延长油田东区下二叠统山西组沉积物受盆地周缘多个物源区的综合影响。从微量元素、稀土元素、主量元素等地球化学及重矿物等方面系统分析了研究区沉积物特征,恢复了该区物源。研究区山西组山2段总体少盐水,山1段以延安地区为界,以南地区少盐水、以北地区中盐水;富集Rb、Th、U、La、Pb、Nd、Gd而亏损Ba、Nd、Ta、Ce、Sr、Eu,山1段和山2段分异度不大;以Y145和Y153—Y120一线为界,前者以北地区及后者以南地区主矿物类型相似,受物源影响含量差异大。研究区山西组沉积物受北北东方向、北北西方向和南方3个物源的综合影响。

The deposit sediments at Shanxi formation in lower Permian series in the east Yanchang oilfield are affected by the comprehensive powers of many provenance areas around many basins. This paper analyzes the sedimentary features of this area from the aspects of ithogeochemistry,such as trace elements,REE and major elements as well as heavy minerals,on whose basis it recovers the provenance. The results show that： firstly,the No. 1 Section of this area mainly consists of low-salinity water in the south and middle-salinity water in the north,while the No. 2 section mainly consists of low-salinity water. Secondly,with the trace elements,it is generally rich in Rb,Th,U,La,Pb,Nd and Gd in varying degrees while poor in Ba,Nd,Ta,Ce,especially Sr and Eu; the two lithologic sections differ little in this aspect. Lastly,the Shanxi formation can be divided into three sections in heavy mineral combinations： the North Section — to the north of Y145,the South Section — to the south of Y153 and Y120,and the Middle Section — between the above two sections; the North and South Sections are the same in the types of main minerals,though different in proportion,but the Middle Section differs much from the two due to the effects of different provenance. It is clear that the sedimentary at Shanxi formation is affected comprehensively by the three provenance areas： north north east,north north west and south.