塔里木盆地库车坳陷三叠纪沉积相与古地理研究

库车坳陷继晚二叠世的厚层磨拉石沉积之后,三叠纪开始进入封闭的挤压挠曲型盆地发展阶段,拉开了中生代前陆盆地发展的序幕,构造格局和构造样式较古生代发生很大转变。盆地内三叠纪气候湿热,沉积相类型多样。靠近北部山前发育大套冲积扇、扇三角洲和辫状三角洲沉积,向坳陷中心有辫状三角洲、曲流河和湖泊沉积。河漫沼泽上发育多套煤层。其滨湖、沼泽相炭质泥岩及煤系建造是库车坳陷重要的烃源岩。在整个三叠纪演化的不同时期,逆冲挤压应力逐渐增强又逐渐减弱,各时期盆地的古地理特征不同。从早三叠世到晚三叠世,盆地的沉积和沉降中心持续南迁,前缘隆起则持续向前陆方向后退。三叠纪前缘隆起和北部逆冲带在轮台以东连通,该连通古陆从早三叠世至晚三叠世持续由东向西移动,但迁移幅度不大,在晚三叠世时期成为一个次要物源区。 

TRIASSIC PALEOGEOGRAPHY AND SEDIMENTARY FACIES OF THE KUQA DEPRESSION,TARIM BASIN

After the deposition of Late Permian thick-bedded molas s es,the Kuqa depression began to enter a stage of development of a closed compres s ional flexural basin in the Triassic,thus ushering in the stage of development o f a Mesozoic foreland basin,when the tectonic framework and style were very diff erent from those in the Paleozoic.The Triassic climate in the basin was wet and hot and the sedimentary facies were very diverse.There are deposits of alluvial fans,fan deltas and braided deltas near the piedmont belt in the northern part.T owards the center of the depression,there are deposits of braided deltas and mea nder ing rivers and lakes.Several coal beds are developed in backswamp deposits.Lakes hore and swampy carbonaceous mudstone and coal measures are major hydrocarbon so urce rocks of the Kuqa depression.In different phases of the entire Triassic evo lution,thrust compressional stresses increased gradually and weakened gradually. The paleogeographic features in various phases were different.From the Early Tri assic to Late Tiassic,the depocenter and subsidence center moved southward progr essively,while the frontal uplift retreated toward the foreland continually.The Triassic frontal uplift and northern thrust belt were connected to the east of L u ntai.This connected oldland moved westward steadily from the Early to Late Trias sic but the magnitude of migration was not large.In the Late Triassic it became a subordinate material source.