Comparison of geochemical characteristics of marine facies, marine-continental transitional facies and continental facies shale in typical areas of China and their control over organic-rich shale

The geochemical characteristics of marine, marine-continental transitional, and continental facies shale and their control over organic-rich shale were discussed. Results showed that the TOC content of marine shale was the highest with an average of 4.95%, followed by the marine-continental transitional shale of Taiyuan Formation, whose average was 3.20%; the continental shale of Shanxi Formation has the lowest TOC content, with an average of 1.64%. There were differences in the lithofacies of the three formations and the marine shale has the highest TOC in siliceous shale, followed by mixed calcareous shale, which were much larger than the Taiyuan and Shanxi Formation shales. The TOC of the Taiyuan Formation was higher than that of the Shanxi Formation in the same lithofacies. In terms of element composition, Al and Si of the three Formations have absolute advantages, but Mg, Na, Ca, P account for a large proportion in the marine shale compared with the other two formations. The shales of the Taiyuan Formation and the Shanxi Formation were deposited in a medium to strong reducing environment, warm and humid paleoclimate as a whole; the ancient water depth of the Shanxi Formation was larger than that of the Taiyuan Formation, and the sedimentary water body was turbulent experienced periodic transgression and regression. Warm and humid paleoclimate, certain oxygen content, and salinity, appropriate water depth, stable water body, and high nutrient element content (such as P) were more conducive to the development of organic-rich shale.