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Organic Geochemical Characteristics of Source Rocks in the Mizhi Region of Ordos Basin

To study the distribution relationship between salt rocks and oil-and-gas in Mizhi region of the Ordos Basin, a detailed research was conducted to assess the organic geochemical characteristics of the source rocks. The results show that the Pr/Ph (pristane/phytane) ratios are higher than 1 and that the content of chloroform bitumen “A” is lower in the Triassic and highest in the Carboniferous strata. From the Triassic to the Ordovician, the maturity is increased but the ratio of aliphatic to aromatic hydrocarbons is decreased with the depth, which is possibly related to the high salinity levels in the region. Long-chain n-alkanes are absent in the Carboniferous, whereas they are observed in the Ordovician. The aromatic chromatograms show that the naphthalene content increases with depth and is consistant with maturity. β-carotene and dehydrovitamin E were detected, which may indicate the presence of marine and reducing environments. The Triassic, Permian and Carboniferous sediments can be classified as source rocks.