鄂尔多斯盆地上三叠统延长组长10油层组沉积特征及物源*

鄂尔多斯盆地上三叠统延长组为大型拗陷湖盆沉积,长10油层组为延长组初始期沉积物。但其物源特征、沉积体系划分、沉积相类型等基础问题尚不清楚,严重制约了全盆地长10油层组的勘探发现。针对这些问题,作者采用了轻重矿物、锆石测年等分析方法,明确了长10油层组主要发育东北、西北、西南三大物源,根据物源特征沉积体系划分为东北、西北和西南沉积体系。综合野外露头、岩心、钻井、测井等资料揭示了长10主要发育河流-三角洲沉积,其中,西北沉积体系主要发育辫状河沉积,东北沉积体系发育曲河流-三角洲沉积,西南沉积体系发育辫状河-三角洲沉积,沉积中心位于太白-宜君一带,为浅湖相沉积。

Sedimentary characteristics and provenance of the Chang 10 interval of Upper Triassic Yanchang Formation in Ordos Basin

The Upper Triassic Yanchang Formation was developed within a large depression basin deposits in the Ordos Basin. Chang 10 interval is the initial deposits of Yanchang Formation. However,its source characteristics,the division of sedimentary system and the type of sedimentary facies remain obscure,which,in turn,restricts the exploration and discovery of the Chang 10 interval in the Ordos Basin. Heavy and light minerals,together with zircon dating,suggest that three main provenances developed in the northeast,northwest and southwest of the Chang 10 interval in Ordos Basin. The sedimentary systems were divided into the northeast,northwest and southwest depositional systems,on the basis of the source characteristics. Comprehensive outcrop,core,drilling,logging and other data reveal that Chang 10 interval mainly contains fluvial and deltaic deposits. The northwestern depositional system is mainly composed of braided river deposits,while the northeastern depositional system is typified by meandering rivers and delta deposits. The southwestern depositional system is represented by braiding river deltas,with sedimentary center located in Taibai Yijun areas(mostly shallow lacustrine facies).