This paper studies the petrologic characteristics of the dawsonite- bearing sandstone reservoirs of the Cretaceous in southern Songliao Basin,the diagenetic sequence of the dawsonite-bearing sandstone, and the occurrence and the origin of the dawsonite based on the principles and the methods of the petrology and the isotope geochemistry. The petrologic study shows that the dawsonite-bearing sandstones are mainly composed of the arkoses and the feldspathic litharenite. The diagenetic sequence is shown to be the clay coating cementation-secondary feldspar overgrowth-secondary quartz overgrowth, authigenic quartz, kaolinite-calcitehydrocarbon charging-CO₂ charging-dawsonite-ankerite. The analysis of the carbon and oxygen isotope composition indicates that the dawsonite δ¹³C_PDB values range from -0.342% to 0.329%, and δ¹⁸O_PDB values range from -1.922% to -0.954%, as is similar to the proved dawsonite formed in the organic background and related to the magmatic activity. The calculated δ¹³C_PDB values of CO₂ gas in the isotope equilibrium with the dawsonite ranging from -0.992% to -0.423%, are consistent with the δ¹³C_PDB values of the inorganic CO₂ in the southern Songliao Basin. These values indicate that the CO₂ that forms the dawsonite and that from the gas reservoir have the same source, which is the mantle-sourced origin.

southern Songliao Basin  /  dawsonite-bearing sandstone  /  carbon and oxygen isotope composition