Carboniferous Lithofacies and Paleogeography of the Hexi Corridor Basins, NW China

The Hexi Corridor Basin Group, renowned for its Carboniferous source rocks, has emerged as a pivotal target for oil and gas exploration. This study integrates fieldwork, drilling, and geochemical data to analyze the Carboniferous lithofacies and paleogeography of the basin group, which is marked by extensive transgressive deposits. The Hexi Corridor experienced three key evolutionary phases during the Carboniferous. During the Early Carboniferous (deposition stage of the Qianheishan and Chouniugou Formations), crustal subsidence formed the Qilian epicontinental sea. Marine water intruded from the southeastern Qinling Mountains, and clastic sediments were supplied by the Alashan and Ordos oldlands to the north, developing lagoon-tidal flat facies interbedded with coal seams. As marine transgression expanded during the deposition of the Chouniugou Formation, the marine domain of the South Qilian area connected with the Beishan Trough, resulting in sedimentary differentiation between barrier-lagoon and open-coast deposits within this region. In the Late Carboniferous (deposition stage of the Jingyuan to Taiyuan Formations), transgression peaked; the marine area extended northward to Jiayuguan and eastward to connect with the North China Sea. Sediment thickness in the Helan Aulacogen changed sharply due to fault movement. This area was dominated by littoral-neritic tidal flat deposits with extensively developed coal seams, and detrital materials were still sourced from the Dunhuang–Alashan and Longxi oldlands. The entire evolutionary process was marked by tectonic control on basin development, multi-directional marine transgression, and persistent terrigenous sediment supply.