Mechanism of Thermochemical Oxidation of Hydrocarbons （TOH） in the clastic strata of sedimentary basins is unclear.In particular， it is urgently needed to clarify the oxidizing substances involved in the reaction and their state of occurrence before and after the reaction. A related study was carried out in the Lower Triassic Baikouquan （T1b） Formation in Junggar Basin， where the TOH reaction has been confirmed in recent years. Based on detailed core logging， systematic petrological and mineral identification， major elements ofbulk rock and in situ area， and chemical valence analysis of iron ions were carried out. The results show that the cores of this formation show obviously irregular distribution of brown and gray-grayish green layers， and the color changesare not limited in lithologic interface and sedimentary structure. Gray-grayish green layers are most likely the products of bleaching of reducible oil-gas bearing fluid during burial diagenesis. Mineral changes indicate that the color transformation from brown to gray-grayish green is the result of the consumption of oxidizing hematite and the generation of chlorite in the rock. Hematite contains a large amount of Fe³⁺ and a small amount of Mn^3+/4+ ions replacing Fe³⁺ by isomorphism.In the T1b formation both Fe³⁺ and Mn^3+/4+ in hematite provide effective electron acceptor for the TOH reaction. Mn^3+/4+ is preferentially involved in reactions， however，the high content of Fe³⁺ was the main electron acceptor， followed by low content of Mn^3+/4+. The content difference of Fe³⁺ and Mn^3+/4+ causes the fact that the reduction product of authigenic chlorite is rich in Fe， whereas Mn is mainly enriched in low content authigenic calcite cements with extremely negative δ¹³C values. Abundant hematite participated in the reaction， indicating that the TOH reaction may occur generally in the deep layers of continental petroliferous basins. This reaction will causealterations in mineral composition， remoldingreservoir rocks， and meanwhile consuming large amounts of hydrocarbons in the crust. It is necessary to carry out further studies on this process， particularly in sedimentary basins and subduction zone.