塔里木盆地东南部石炭系、二叠系沉积与层序特征

CARBONIFEROUS-PERMIAN SEDIMENTOLOGY AND SEQUENCE STRATIGRAPHY IN THE SOUTHEAST PART OF THE TARIM BASIN

塔里木盆地东南部中石炭统-下二叠统是一个顶底为Ⅰ类不整合所限定的二级沉积层序。该层序沉积期,塔里木盆地东南部存在三个古陆,两个浅海海峡,一个半深海斜坡。随着海平面上升-静止-下降于不同部位形成了不同沉积体系及组合。海进体系域由中上石炭统的滨岸破坏性三角洲和开阔台地碳酸盐岩体系组成,内部又存在三个三级海面升降周期,高位体系域由下二叠统的滨浅海-三角洲-河流体系组成,内部伴随多次三级海面振荡及其由此引起的沉积特征的变化。

The Middle Carboniferous-Lower Permian in the Tarim basin is a depositional sequence bounded by type 1 unconformites. During the depositional period of this sequence, there were three paleocontinents, two straits and a bathyal slope in the southeast part of the Tarim basin. With the eustatic change, various assemblages of paralic clastic rocks and marine carbonate rocks formed in different areas. The Middle Carboniferous Kalawuyi Formation and Azgan Formation and Upper Carboniferous Tagarqi Formation are three transgressive-retrogressive parasequence sets which make up a transgressive system tract of a second-order sequence, consisting of coastal destructive delta facies and open platform carbonate facies. The Lower Permian Pusige Formation is a progradational parasequence set pertaining to the highstand system tract, composed of fluvial-deltaic-litteral-neritic facies. The slope depositional systems have been folded and cropped out. The condensed section which formed at the end of the Late Carboniferous consists of alternating thin beds of black shale and marl 20 - 40 m thick. It can be a good oil source rock. The braided delta sand at the base of the transgressive-system-tract Tagarqi Formation and the Early Permian delta sand of the highstand-system-tract may be better reservoirs.The comparison of relatively eustatic curve of the southeast Tarim basin with that of Vail's second-grade global sea level suggests that the southeast Tarim basin was locally uplifted during the Early Carboniferous, which caused the sea level drop and stratigraphic missing. The eustatic curve of the Middle Carboniferous-Early Permian are correlable with the global one.