鄂尔多斯盆地西南部上三叠统长6油层组湖底扇特征

Sedimentary characteristics of sublacustrine fan of the Interval 6 of Yanchang Formation of Upper Triassic in southwestern Ordos Basin

通过岩心观测、薄片观察和各种资料的综合分析,对鄂尔多斯盆地西南部上三叠统延长组长6油层组湖底扇的岩石类型、粒度特征、沉积构造等特征进行了详细研究。研究结果表明长6油层组浊积岩的岩石类型为长石岩屑砂岩、岩屑长石砂岩和长石砂岩;浊积砂岩的矿物成分成熟度低,结构成熟度较低,杂基含量高。粒度分析表明其具有典型的浊流特征。沉积构造可见递变粒序、底层面构造、滑塌角砾,且发育鲍马序列;反映了浊积岩具有明显的韵律性和旋回性。识别出薄层浊积岩、中层浊积岩、厚层浊积岩3种类型并分别描述其特征。在此基础上进行了亚相划分,详细描述了各亚相特征,确定了浊积岩分布在庆阳、合水、固城、安置农场地区。浊积岩的形成主要受外界的触发机制、充足的物源供给、古斜坡地形等因素控制。

By a comprehensive analysis of cores and thin sections and other data, detailed studies have been made on the rock types, granularity and sedimentary structures of the sublacustrine fan of Interval 6 of Yanchang Formation of Upper Triassic in the southwestern Ordos Basin. The results show that the Interval 6 of Yanchang Formation is composed of lithic feldspathic sandstones, feldspathic lithic sandstones and feldspathic sandstones. The compositional and textural maturities of turbidites are low while the matrix content is high. The granularity analysis results show typical features of turbidite deposits. Grading sequence, burthen structures, and the Bouma Sequence are developed in the turbidites sliding structures, which demonstrate obvious features of both the rhythmicity and the cyclicity. Totally 3 kinds of turbidites have been recognized and described, including thinly-bedded, mediumly-bedded and thickly-bedded turbidites. On the basis of this investigation, subfacies are identified and their characteristics are described. The turbidites are mainly developed in the Qingyang, Heshui, Gucheng and Anzhinongchang areas and are controlled by exterior triggering mechanism, aboundant sediment supply, paleo-slope and so on.