Discussion on Original Organic Types of Over Over-mature Source Rocks in Wuli Permafrost Zone of Qinghai-Tibeatean Plateau

In order to find out the original organic types of Wuli permafrost zone on Qinghai-Tibetan Plateau, the cores core samples are taken analyzed which are from gas-hydrate drilling hole (called referred to as ZK1) and its adjacent drilling holes are analyzed. The results show that the kerogen maceral from the ZK1 and adjacent drilling holesstudy area is mainly composed of vitrinite, accounting for 79.68%—83.62%, and some inertinite with a proportion of, respectively accounting for 79.68%—83.62% and 14.19%—18.35%. Therefore, it is can be inferred that the kerogen could be of Type Ⅲtype. On the baseis of biomakers, the ratios of Pr/nC₁₇ and Ph/nC₁₈ respectively get to 0.29—1.05 and 0.57—1.56, while the ratios of C₂₃ tricyclic diterpane/C₃₀ hopane and C₂₇/C₂₉ sterane respectively reach to 0.47—2.23 and 0.64—1.35. It will can be seen from these data that the kerogen could be classified into fall into TypeⅡ₁ or TypeⅡ₂ type. Considering that the fact that maturity of source rocks reaches to are in over mature evolution stage, it it could be summarized a conclusion that the original organic type of the source rocks was probably belongs to mixed typea mixture, while with some organic matters mainly could be originated mainly from inferior aquatic organisms.