235 / 2022-03-22 21:46:14

Lithofacies Characteristics and Sedimentary Process of Fluvial to Alkaline Lake System Influenced by Volcanoes: A Case Study From Permian Fengcheng Formation in Mahu Sag, Junggar Basin, China

Lithofacies, lithofacies association, depositional model, fluvial to alkaline lake system, Fengcheng Formation, Mahu sag

Fengcheng Formation in Mahu sag is characterized by complex lithology, uncertain distribution regularity and controlling factors of lithofacies, diversified lithofacies associations, and unclear understanding of sedimentary process and distribution range of facies. It is necessary to more systematically summarize the types and genesis of lithofacies, and more comprehensively identify the types and genesis of lithofacies association, so as to more accurately predict the distribution and evolution of facies. The division of lithofacies and identification of lithofacies association are carried out by using core and rock thin section data, and the distribution characteristics and evolution regularity of sedimentary facies are analyzed in combination with logging data and seismic data. Fengcheng Formation can be divided into six primary lithofacies: conglomerate, sandstone, siltstone, mudstone, evaporite and volcanic rock. Combined with bedding types, 34 secondary lithofacies can be subdivided. Fengcheng Formation can identify 10 kinds of lithofacies associations, such as channel on the plain, non-channelized delta front and underwater distributary channel. Volcanism is mainly developed in the northern slope of Mahu sag, followed by the western slope of Mahu sag. The fluvial delta system is developed in the northern slope, western slope and southern slope of Mahu sag, and is most developed in the western slope. Fluvial delta system is not developed in the eastern slope of Mahu sag, and beach bar deposits are mainly developed. Alkaline mineral rocks are mainly developed in Central area of Mahu sag. The fluvial to alkaline lake sedimentary model affected by volcanoes established in this study provides sedimentological support for the exploration and development of Fengcheng Formation in Mahu sag.