陇东地区上三叠统延长组早中期物源分析与沉积体系

Source analysis and depositional systems of Upper Triassic early and mid-term Yanchang Formation in Longdong area

利用轻重矿物组合特征、古水流方向、砂岩岩石学特征、水下分流河道砂体空间展布及沉积构造特征等,对鄂尔多斯盆地陇东地区上三叠统延长组长8-长6油层组母岩类型、物源方向以及沉积体系进行研究。古流向参数表明,延长组沉积时期,沉积物从盆地边部向中心搬运。根据轻重矿物组合划分出3个主要物源方向,即西、西南和东北方向。此外,根据古流向判断有南部的次要物源。母岩是盆地周缘的前寒武系石英岩、中基性、中酸性火山岩、变质岩和古生界的浅变质岩、碳酸盐岩和砂砾岩。陇东地区上三叠统延长组长8-长6油层组沉积体系划分为:北东向吴旗-华池三角洲沉积体系和西部环县扇三角洲沉积体系,西南部镇原-泾川辫状河三角洲沉积体系和南部合水-固城川浊积扇沉积体系。在沉积体系划分的基础上,详细阐述了不同沉积体系的岩石学特征、砂体形态和沉积构造及各沉积体系的演化过程。

Light and heavy mineral combination characteristic, directions of palaeo-flow, sandstone petrography, space distribution of sand bodies of subaquatic distributary channels and sedimentary structure feature were used to analyze source rock ,source direction and depositional system of Chang 8-6 oil-beds of Yanehang Formation of the Upper Triassic in Longdeng area of Ordos Basin. The palaeo-flow parameters show that the sediments are carried from department by the basin to the center in the depositienal period of Yanchang Formation. Three main source directions can be divided according to the light and heavy mineral combination characteristics, as west, southwest and northeastern directions. In addition,there is the secondary source in the south according to ancient flow direction. The quartzite, neutral-basic and neutral-acid volcanic rock, metamorphic rock of Preeambrian and shallow metamorphic rock, carbonate rock , gravel rock of Palaeozoic group from basin outer edge are the source rocks. The depositional system of Chang8-6 oil-beds of Yanchang Formation of the Upper Triassic in Longdong area can be divided into four systems. One of them is Wuqi-Huachi delta depositional system from northeast; others are Huanxian fan delta depositional system from west, Zhenyuan- Jingchuan braided delta depositional system from southwest and Heshui-Guchengehuan turbidite fan depositional system from south. On the basis of the depositional systems, petrographic characteristics, sand body pattern, sedimentary structure of different depesitional systems and the evolution process of the depesitional systems are elaborated in detail.