Sequence stratigraphic filling model of the Cretaceous in the western Tabei Uplift, Tarim Basin, NW China

Abstract

Abstract Cretaceous formation in the western Tabei Uplift is significant petroleum pay zone in the Tarim Basin, NW China. For the complex relationship between tectonic movement and depositional environment, sequence stratigraphic filling model of the whole Cretaceous formation has not been established yet. Using well logs and seismic data in this article, sequence stratigraphic evolution process and filling model of the Cretaceous are interpreted involving paleo-uplift, sedimentary and water-level. As a first-order sequence, the Cretaceous is subdivided into three second-order sequences, Shushanhe, Baxigai and Bashijiqike Formation. Shushanhe Formation is subdivided into three third-order sequences, KSQ1, KSQ2 and KSQ3 upwards; Baxigai Formation is considered as one single third-order sequence, KSQ4; Bashijiqike Formation is subdivided into three third-order sequences, KSQ5, KSQ6 and KSQ7 upwards. In the early KSQ1, paleo-uplift was aquatic. From KSQ1 to KSQ3, water-level raised and paleo-uplift moved upwards gradually; and water-level raising was faster than paleo-uplift ascending. The accommodations of these three sequences increased. Lacustrine facies mudstones and siltstones were onlap filling sequences towards Xiqiu Paleo-uplift. In the end of KSQ3, the whole region was subaqueous. The water-level and paleo-uplift in KSQ4 were easy steady, and the accommodation in KSQ4 was sustained. Delta depositional system began to prograde from depocenter to distal slope of paleo-uplift. In the high of Xiqiu Paleo-uplift, dominated sediments were fine grains for the sedimentary dynamic force. From KSQ5 to KSQ7 in the Bashijiqike Formation, water turned regression, paleo-uplift raised slowly and the accommodation reduced continually. Because of the progradation deltaic sandstones, downlap sequences were developed towards the Xiqiu Paleo-uplift. Exposed in the Early Paleogene, KSQ7 and part KSQ6 were truncated to form top unconformable boundaries. Established sequence filling model of the Cretaceous in the western Tabei Uplift provides important insights on the stratigraphic characteristics and in turn on the exploration potential of petroleum systems.