库车坳陷白垩系巴什基奇克组泥砾的成因机制与厚层状砂体展布

库车坳陷白垩系巴什基奇克组大面积厚层状砂体为塔里木油田重要的产气层段，厚层状砂岩的沉积环境研究一直存在争议。在厚层状砂岩中，普遍发育有褐色泥质砾石和少量粉细砂质砾石，明确与厚层砂岩相伴生的砂泥质砾石成因机制与沉积环境，可从全新角度来探讨大面积厚层状砂岩的沉积环境。通过野外露头与多口钻井的岩心观察，分析泥质砾石组成矿物成分及含量，将泥质砾石、粉细砂质砾石按照成分、形态及赋存状态（产状）进行了种类划分。依据砂泥质砾石成分判断其主要来自于厚层砂岩附近褐色粉砂质泥岩，进而采用“将今论古”的方法，发现在现代塔里木河（季节性曲流河）、赣江浅水三角洲上平原-下平原环境中，发育有泥质砾石沉积，并结合前人成果，综合类比分析后认为厚层砂岩中的砂泥质砾石具有同样的成因机制与发育环境。研究表明巴什基奇克组中的泥质砾石、砂质砾石为季节性河流及/或季节性河流浅水三角洲上平原-下平原（受间歇湖水影响区）环境下的产物，即属于处于陆上、间歇有湖水影响的沉积环境下的产物，并非长时期处于“水下”的三角洲前缘-滨浅湖环境下的产物。砂泥质砾石的成因机制为：河道堤岸沙泥质垮塌、原地堆积而成；堤岸沙泥质垮塌后短距离搬运而成。受此启示，认为巴什基奇克组厚层砂岩主要发育于季节性河流以及季节性河流浅水三角洲上平原-下平原的沉积环境。

Mechanism and sedimentary environment of the muddy gravel concomitant with thick layer sandstone of Cretaceous in Kuqa depression

The large-area thick-layer sandstones in Cretaceous Bashijiqike Formation, Kuqa depression are important gas horizons of Tarim Oilfield. Disputes have always existed in research of the sedimentary environment of thick-layer sandstone. Brown muddy gravels and a small number of silty-fine sandy gravels are generally developed in thick-layer sandstones. The genetic mechanism and sedimentary environment of arenaceous pelitic gravel associated with thick-layer sandstone can be clarified to explore the sedimentary environment of large-area thick-layer sandstone from a brand new perspective. Based on field outcrops and core observation of multiple drilling wells, the mineral components and contents of muddy gravel are analyzed. On this basis, the types of muddy gravel and silty-fine gravel are divided according to the component, morphology and occurrence state. Based on component analysis, arenaceous pelitic gravel is judged mainly from gray silty mudstone adjacent to thick-layer sandstone. Using the uniformitarianism method, it is further discovered that muddy gravel sediments are developed in modern Tarim River (seasonal meandering river) and upper plain-lower plain of Ganjiang shallow water delta. Based on comprehensive analogy analysis in combination with previous research results, it is considered that the muddy gravel in thick-layer sandstone has the same genetic mechanism and development environment. This indicates that the muddy gravel and sandy gravel in Bashijiqike Formation are products under the environment of seasonal river or upper plain-lower plain of seasonal river shallow delta (influence area of intermittent lake), i.e., the products in the onshore sedimentary environment influenced by intermittent lake, rather than the products in the "underwater" delta front-shore-shallow lake environment for a long term. The genetic mechanism of sandy gravel includes two aspects, i.e., autochthonous deposit and short-distance transport after arenaceous pelitic collapse of river bank. Accordingly, it is believed that the thick-layer sandstone in Bashijiqike Formation is mainly developed in the sedimentary environment of seasonal river and upper plain-lower plain of seasonal river shallow delta.