TRIASSIC PALEOGEOGRAPHY AND SEDIMENTARY FACIES OF THE KUQA DEPRESSION,TARIM BASIN
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摘要: 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。Abstract: After the deposition of Late Permian thick-bedded molasses,the Kuqa depression began to enter a stage of development of a closed compressional flexural basin in the Triassic,thus ushering in the stage of development of a Mesozoic foreland basin,when the tectonic framework and style were very different 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.Towards the center of the depression,there are deposits of braided deltas and meandering rivers and lakes.Several coal beds are developed in backswamp deposits.Lakeshore and swampy carbonaceous mudstone and coal measures are major hydrocarbon source rocks of the Kuqa depression.In different phases of the entire Triassic evolution,thrust compressional stresses increased gradually and weakened gradually. The paleogeographic features in various phases were different.From the Early Triassic to Late Tiassic,the depocenter and subsidence center moved southward progressively,while the frontal uplift retreated toward the foreland continually.The Triassic frontal uplift and northern thrust belt were connected to the east of Luntai.This connected old land moved westward steadily from the Early to Late Triassic but the magnitude of migration was not large.In the Late Triassic it became a subordinate material source.
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Key words:
- Kuqa depression /
- Triassic /
- sedimentary facies /
- paleogeogra phy
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