Redefinition of the Jurassic Strata of the Mazha Tectonic Melange in West Kunlun

In the Yecheng County, there exists a set of coal-bearing sandy conglomerate formation in the Mazha tectonic mélange of West Kunlun. Shaanxi Geological Investigation Institute divided this formation into three units in the 1:250000 regional geological survey, i.e. Triassic (T, non-layered), Triassic Sailiyakedaban Group (TS), and early-middle Jurassic Yarkant Group (J_1-2Y). These clastic rocks were mainly intermountain molasses formed by orogenesis, but the contacts between all strata were faults. Except for the incomplete top and bottom, the sedimentary sequence and age of all strata were also without knowledge. By the measurement and analysis on the clastic rocks, and according to the rock assemblages and biostratigraphic characteristics, this set of coal-bearing sandy conglomerate can be redefined as early-middle Jurassic Yarkant Group which can be further divided into three units from the bottom to the top: the Shalitashi Formation (J₁s^), Yangye Formation (J₂y), and Targa Formation (J₂t). They were fluviolacustrine strata and sedimentary response to the early-middle Jurassic orogenesis in the tectonic mélange belt of West Kunlun.