|
Li Liu, Jilin University (China)
Yuqiao Gao, Nanjing University (China)
Xiyu Qu, Jilin University (China)
Xiaolei Peng, Jilin University (China)
Na Liu, Jilin University (China)
|
|
The Cretaceous dawsonite-bearing sandstone is locally distributed in Hailaer Basin and Songliao basin, China. The types, paragenetic sequence of authentic minerals and origin of CO2 forming dawsonite in dawsonite-bearing sandstone are investigated using Palarizering micoscope, scanning electron microscope, x-ray diffraction and MAT-251 or MAT-253 stable isotope mass spectrometer. The results show that dawsonite-bearing sandstones are fine-grained or fine- to medium- grained, poorly to moderately sorted arkoses and lithic arkoses. The dominant cements are quartz overgrowth, authigenic quartz, dawsonite, ankerite and clay minerals. The diagenetic paragenesis includes six discrete diagenetic processes in order of occurrence: (1) clay mineral coatings; (2) quartz overgrowth, kaolinite; (3) petroleum charging; (4) CO2 charging; (5) dawsonite; (6) ankerite. Pre-CO2 minerals include quartz overgrowth, authigenic quartz and kaolinite, and the main cements are dawsonite and ankerite after CO2 charging. Dawsonite δ13 C values from -5.3 to +0.3‰PDB. The calculated δ13 C of CO2 gas being in equilibrium with dawsonite range from -10.7 to -6.9‰PDB, is in coincidence with δ13 C values ranging from -11. 36 to -5.74‰PDB of CO2 gas in Hailaer basin and songliao basin. These values indicate that CO2 both forming dawsonite and from gas reservoir originated from mixture background of inorganic and organic CO2, mostly from inorganic CO2. According to the fact that both dawsonite-bearing sandstone and CO2 gas reservoir lie in the vicinity of fault zone and later Cretaceous or even younger igneous rocks, CO2 both from gas reservoir and forming dawsonite is attributed to the magmatic activity.
|
