Carboniferous-Permian marine lithostratigraphy and sequence stratigraphy in Xi Ujimqin Qi, southeastern Inner Mongolia, China

On the basis of 1:250000 regional geological survey, the authors made a lithostratigraphic study and redivision of the Carboniferous-Permian strata in the Xi Ujimqin Qi-Linxi area, southeastern Inner Mongolia, and used the biostratigraphic, sequence stratigraphic and unconformity approaches to make multiple stratigraphic division and correlation. They studied the essential sequences, depositional environment and sedimentary facies and divided the Carboniferous-Permian strata into three depositional sequences and established the lithostratigraphic and chronostratigraphic frameworks. The view that the Carboniferous-Early Permian Gegen Obo Formation (CPg), Bumbat Formation (CPb) and Amushan Formation (CPa) are contemporaneous but heteropic strata in the Carboniferous-Permian Xi Ujimqin Qi sea trough can well explain the mutual relation of these stratigraphic units. The Shoushangou Formation (P1ss)overlaps unconformably on pre-existing strata or geologic bodies; the Dashizhai Formation(P2ds) is the product of submarine volcanic eruption at the time of a maximum marine-flooding surface; and the Zhesi Formation (P2Z) is the production of deposition during shrinkage of a sea basin.