Sedimentary environment and controlling factors of carotane development: a case study of Linhe Depression in Hetao Basin

Carotane is a good indicator in sedimentary environment and oil-source correlation. gamma-carotane and beta-carotane are important biomarkers of source rocks in Linhe Formation, Linhe Depression, Hetao Basin. In this study, 22 mudstone samples were collected, and total organic carbon, rock-eval pyrolysis and Saturated hydrocarbon gas chromatography-mass spectrometry experiments were carried out to determine the hydrocarbon potential of Linhe Formation source rocks and the controlling factors for the development of carotane. Total Organic Carbon (TOC wt%) of the samples value 0.44-1.90%, and S1+S2 value 0.46-10.39mgHC/g Rock. The organic matter types are mainly type II1 and type II2, which are in the low mature-maturity stage, indicating that the source rocks have high hydrocarbon potential. Pr/Ph values 0.14-1.76, Gam/C30H values 0.11-1.89, C27/C29 values 0.28-0.69, indicating a strong reduced brackish water-brackish sedimentary environment. The source material was mainly higher plants, with less aquatic bacteria and algae. In the strong reducing environment of salt water, the bloom of algae and bacteria is conducive to the development of carotane, which is basically not affected by maturity. This study enriches the study of geochemical system of source rocks and provides a new case for the study of sedimentary environment of oil and gas basins in the world.