Main Controlling Factors and Modes of Organic Matter Enrichment in Salt Lake Shale

In order to further study the enrichment mechanism of the 10 rhythm of the third (Eq3) members(Eq3₄¹⁰ for short) and partial rhythm of the forth (Eq4_low)members shale organic matter in the Qianjiang Formation of the Qianjiang sag, Jianghan basin under the background of salt lake, X-ray fluorescence spectroscopy (XRF), carbon sulfur analyzer, GC, GC-MS and other methods were used to understand the relationship between elemental changes and TOC enrichment of shale in this area, so as to analyze the main controlling factors of organic matter enrichment and establish organic matter enrichment mode. The results show that organic matter is more concentrated in the transgressive systems tract (TST), and is poor in the highstand systems tract (HST) and the lowstand systems tract(LST). Organic carbon is positively correlated with paleoproductivity index (P/Ti), paleoclimate index (Mg/Ca) and paleo-water depth index (Rb/K), and the organic matter increases first and then decreases with the increase of the ancient salinity index (Sr/Ba). Land-based material input and the quantitative parameters (SiO₂, Al₃O₂) are negatively correlated with organic carbon. And when P/Ti >1, 2 < Sr/Ba < 4, Mg/Ca < 0.4, Rb/K >0.007 and the input of terrigenous matter is less, the organic matter is more concentrated. The study reveals that the source of organic matter in the shale of the Qianjiang Formation in the Qianjiang sag is mainly aquatic organisms. Under the relatively humid paleoclimate conditions, the aquatic organisms prosper, and the input of terrigenous debris is low, which weakens the dilution of organic matter. At the same time, more precipitation makes the lake water depth increase rapidly, the surface water body salinity decreases, and the lake bottom salinity is larger, which results in salinity stratification and enhances the reduction of deep lake water and is conducive to the enrichment of organic matter.