Cambrian infill sequence and sedimentary evolution in southwestern Tarim Basin

In the southwestern Tarim Basin, studies on the paleo-uplift and shelf divergence have focused on the sedimentary evolution and sequence filling during the Cambrian period. This research used zircon U-Pb dating and well-seismic technologies. The findings indicate that Cambrian deposits overlay the basin's basement structures, particularly in the Bachu uplift area. The Cambrian sedimentation patterns closely mirror the underlying basement tectonics. Influenced by these tectonics, along with tectonic movements and sea-level changes, four distinct sequences emerged in the Cambrian: the Yuertusi to Xiaoerbulake formations, the Wusonggeer to Shayilike formations, the Awatage Formation, and the Lower Qiulitage Formation. Additionally, seven sedimentary facies and ten depositional sub-facies were identified. From the first to the third Cambrian sequence, spanning the early to middle Cambrian, the area transitioned from a platform to a gentle slope, then to a steeper slope and finally to a deep shelf. This progression indicates a retreat towards the sea, fostering the development of Cambrian source rocks. In the late Cambrian, during the fourth sequence, the southwestern Tarim Basin transformed into a restricted platform. This period marked the establishment of the sedimentary framework in the Tarim Basin, with distinct eastern basin and western platform regions.