The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

The shale of the Wulalike Formation developed in northwestern Ordos Basin is considered to be an effective marine hydrocarbon source rock. One key factors for successful gas exploration Wufeng–Longmaxi Sichuan high content biogenic silica. However, few people have studied siliceous origin shale. In this study, we used petrographic observation and element geochemistry analyze silica results show that minerals are not affected by hydrothermal mainly consist detrital A large number organisms, such as sponge spicules, radiolarians, algae, found under microscope. It has been demonstrated total organic carbon a positive correlation with negative silica, one indicators paleoproductivity. Therefore, enrichment matter may related Through calculation logging data well A, it distributed bottom Formation, decreases, while increases upward Formation. Biogenic exists form microcrystalline quartz, which can interconnected rigid framework improve hardness brittleness Meanwhile, quartz protect pores from mechanical compaction. easier fracture at A.