Sedimentary evolution of the Jurassic basin groups in Central Tianshan, Xinjiang

The sedimentary basins in Central Tianshan, Xinjiang were composed, during the Jurassic, of the Yining-Zhaosu, You'erdusi and Yanqi-Kumux Basins, where the huge alluvial-lacustrine clastic deposits were laid down. The clastic deposits may be grouped into six sedimentary facies, eighteen subfacies and forty-four microfacies. During the Early Jurassic to the Xishanyaoan of the Middle-Early Jurassic, the humid climates, flourished plants and abundant swamps and marshes in the study areas facilitated the formation of abundant coal seams. From the Toutunhean of the Middle Jurassic onwards, the climates became progressively arid. The Lower Jurassic Sangonghe and Xishanyao Formations were once dominated by the braided river deposits and braided delta deposits. The black shales and coal seams of the Badaowan Formation in the abyssal-bathyal lake facies are believed to be highly prospective.