Paleoenvironmental conditions, organic matter accumulation, and unconventional hydrocarbon potential for the Permian Lucaogou Formation organic-rich rocks in Santanghu Basin, NW China

Organic-rich rocks have received increasing attention for they are essential for evaluating hydrocarbon potential and unravelling the interaction between Earth surface environments and the biosphere. In this paper, we performed a combination of mineralogical, inorganic and organic geochemical analyses on a 200-m core of the Permian Lucaogou Formation organic-rich rocks obtained from Santanghu Basin, NW China, to investigate paleoenvironmental conditions, organic matter accumulation, and hydrocarbon potential. The redox- and salinity-sensitive proxies (e.g. V/Cr, V/(V+Ni) and Sr/Ba, Rb/K, B/Ga, and B content), together with the wide distribution of pyrite and carbonate minerals in these dark, thinly laminated organic-rich rocks, suggest that dysoxic-anoxic, brackish-saline, alkaline conditions prevailed during the deposition of the Lucaogou Formation in the Santanghu Basin. The occurrence of hydrothermal minerals, including strontianite and barite, and enrichments of B (up to 158.0ppm), Mn (up to 1291ppm), and certain incompatible elements (Li (up to 923ppm), Rb (up to 848ppm), Sr (up to 1760ppm), Hf (up to 12.7ppm)) as well as Ni vs. Co vs. Zn and Fe vs. Mn vs. (Cu+Co+Ni)×10 ternary diagrams demonstrate that the Lucaogou Formation received hydrothermal input during deposition, which suggests hydrothermalism was the source of brine that has caused the salinization of the water column.