摘要:
库车坳陷中生代呈北陡南缓的箕状，其内连续沉积了一套厚度巨大的冲积—湖泊碎屑沉积体。湖缘扇三角洲、辫状河三角洲及曲流河三角洲非常发育，它们的特征清楚、区别明显：（1） 扇三角洲为突发的、瞬时的灾变事件产生的重力流沉积与间灾变期正常牵引流沉积交替进行，并以重力流沉积占主导地位：其平原亚相类似于冲积扇沉积，河道砂体呈透镜状，厚度小、变化大。（2） 辫状河三角洲为正常的河流牵引流沉积，通常受到湍急洪水控制，为季节性沉积作用产物；平原亚相类似于辫状河沉积；河道沉积发育，砂体总体呈层状，内部由若干个下粗上细的河道砂岩透镜体相互叠置而成，交错层发育，尤以侧积交错层异常发育为特征，岩性以颗粒支撑的砂砾岩为主。（3） 曲流河三角洲为正常的河流牵引流沉积，沉积物输入量为相对连续的终年河流的产物，平原亚相类似于曲流河沉积：河道砂体呈层状，交错层发育，类型丰富。当然，这三种类型三角洲之间亦存在着密不可分的内在联系，不仅同一时期内可以并存，而且随着地质历史的演化可相互转化。
Abstract:
Kuche Depression,situated in the northern part of Tarim Basin, is a "dustpan”shaped depression with steep slope in north side and gentle slope in the south side in Mesozoic Era.There is a set of hugely thick,alluvial—lake classic deposition system in it.Three types of deltas and they are recognized:fan-deltas,braided-river deltas and meandering-river deltas and they are very abundant in the lake margin.Their characters are distinct and distinctions are clear:(1)fan-deltas,formed where an alluvial fan is deposited directly into lake from an adjacent highland, are alternatively deposited by gravity flows sediments,formed by gusty、momentary and catastrophic event,and tractive current sediments,formed between catastrophic events,gravity current sediments are dominant in fan-deltas.Delta plain subfacies are similar to alluvial fan facies,and channel bars take the form of lentiform and their thickness is small and various.(2)braided-river deltas,formed where a braided fluvial system progrades into a lake,are deposited by river tractive current sediments,controlled by torrential flood in general,and are seasonal sediments,of which the delta plain subfacies are similar to braided river facies,channel bars are abundant,overall,sand bodies take the form of layered bodies,but internally,they are composed of many finer-upward lenticular sand bodies that pile up each other,cross-beddings are abundant,and especially,exceedingly rich lateral accretion cross-beddings are the distinct character of braided-river deltas.The rock types of this kind delta are mostly grain-supported sandstones and conglomerates.(3)meandering-river deltas,formed where a meandering fluvial system progrades into a lake,are deposited by river tractive current sediments that are correspondingly continuous river production,of which the delta plain subfacies are similar to meandering river facies,and channel bars take the form of layered bodies,with abundant cross seddings.Certainly,there is close inherent relationship in three types of deltas,not only coexist at the same term,but also transform along with geologic development.
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