INFLUENCING FACTORS OF ORGANIC CARBON ACCUMULATION IN BLACK SHALE OF MARINE SEDIMENTARY ENVIRONMENT: A CASE STUDY IN THE NORTHERN PART OF YUNNAN-GUIZHOU AREA, CHINA

In this paper, taking the Longmaxi Formation shale of the YS118 well in the northern part of Yun-nan-Guizhou, China as an example, the controlling factors of organic carbon accumulation in black shale were analyzed using organic carbon, trace elements, rare earth element test data and statistical results on the abundance of the graptolite. The results showed that the TOC content in the lower part of the Longmaxi Formation increased with the increase of depth, and the abundance of the graptolite controlled the degree of organic carbon accumulation. The correlation coefficient between the abundance of the graptolite and the Ba element is about 0.4. In addition to the graptolite, the algae also controls the size of the ancient productivity. The anoxic deposition environment indicated by the redox index such as V/(V+Ni), V/Cr, Ni/Co and U/Th is more conducive to the accumulation of organic carbon, followed by the oxygen-depleted deposition environment. For the deposition rate characterized by (La/Yb)N value, as the TOC increases, the deposition rate is lower, and the lower deposition rate is favorable for the aggregation of organic carbon. The Late Ordovician-Early Silurian series of tectonic movements, on the one hand, formed a deep water sedimentary environment in the study area and provided a good place for the development of the Longmaxi Formation shale. On the other hand, it also promotes changes in paleoproductivity and redox conditions, forming a sedimentary environment conducive to the accumulation of organic carbon.