Chemostratigraphy and shale quality of the first member of Cretaceous Qingshankou Formation in the Gulong Sag, Songliao Basin

The first member of Cretaceous Qingshankou Formation in the Gulong Sag of Songliao Basin is rich in shale oil resources, which has become one of the most important exploration targets of lacustrine shale oil in China. Based on X-ray fluorescence element analysis, X-ray diffraction analysis, total organic carbon, rock pyrolysis, scanning electron microscope and nitrogen adsorption, the paleo-environment was reconstructed by comprehensive utilization of integrated prediction error filter analysis research method of chemical stratigraphy, and its relationship with organic geochemistry, mineralogy and pore structure was discussed. The results indicated that the first member of Qingshankou Formation was deposited in the environment with fresh water-brackish water, semi-deep/deep water and strong reduction. The evolution of paleo-environment during the deposition of Qing 1 member changed from bottom to top, with increasing water depth, decreasing salinity and oxygen content. Paleo-salinity was positively correlated with total organic carbon, residual hydrocarbon and carbonate mineral content. From bottom to top, the contents of carbonate and chlorite decreased, while the contents of plagioclase and clay minerals increased slightly. The pores were dominated by intra-illite pores, intra-I/S mixed-layer pores and intra-pyrite pores. Some intra-plagioclase pores and calcite dissolution pores were developed, and the organic matter pores is slightly few. Nitrogen adsorption data showed that the dominate pore size was 40-53 nm and 3-4 nm. This study clarifies the paleo-environmental evolution of the Gulong Sag, and may shed lights on lacustrine shale oil accumulation and sweet-spotting. Cited as : Guan, M., Wu, S., Hou, L., Jiang, X., Hua, G., Su, L. Chemostratigraphy and shale quality of the first member of Cretaceous Qingshankou Formation in the Gulong Sag, Songliao Basin. Advances in Geo-Energy Research, 2021, 5(3): xx-xx, doi: 10.46690/ager.2021.03.03