Based on TOC distribution

gas chromatograms of saturated hydrocarbons and types of organic matter in various source rocks

this paper studies sedimentary environments of source rocks and their effects on abundance and types of organic matter. Source rocks in Yili basin are mainly distributed in the Permian Tamuqisayi and Basiergan Formations deposited in a weakly reducing to reducing environment in temperate climate

where the water body is characterized by relatively high palaeo-salinity with faintly alkaline to alkaline aqueous medium. Sedimentation zones with strong reduction and relatively deep water body are favorable places for deposition and preservation of original organic matters

thus the source rocks have abundant organic matters of favorable types.