Uplift event in the middle Hercynian period and its influence on the sedimentary-tectonic pattern of the western Tarim Basin

An uplift event in the middle Hercynian period in the western Tarim Basin was called "Bachu Movement" by early researchers, and mainly occurred between the Xiaohaizi Formation and the standard limestone sequence. Some researchers denied its existence, some researchers believed that it occurred between the Xiaohaizi Formation and the limestone sequence, some other researchers believed that it occurred between the upper mudstone sequence and the sandstone-mudstone sequence, and most researchers did not mention it. According to well-strata contrast and seismic interpretation and tracking, the authors have concluded that a tectonic uplift event occurred between the upper sandstone sequence and the sandstone-mudstone sequence in the Kalashayi Formation, which led to the erosion of the upper mudstone sequence, the standard limestone sequence and the middle mudstone sequence in the Kalashayi Formation and even the Bachu Formation. Afterwards, seawater encroached from the southwestern Tarim Basin towards north and east, and the sandstone-mudstone sequence and limestone sequence in the Mazhatage Formation and the Xiaohaizi Formation were deposited. The Bachu Movement occurred between the middle and late stages of the Datang period of the Early Carboniferous, and made the southwestern Tarim Basin reverse from a north dipping slope to a south dipping one. Hydrocarbons expelled from the Cambrian and Ordovician mature source rocks migrated to the north instead of south. The structural belts formed in the late Hercynian period on the Mengaiti Slope and the Bachu Uplift are favorable areas for hydrocarbon accumulation. The Hetianhe, Niaoshan, Bashituo, Yasongdi gas fields and the Haimiluosi gas-bearing structure have been discovered.