Petrology and isotopic geochemistry of dawsonite-bearing sandstones in Hailaer basin, northeastern China

• Published in: Applied geochemistry 2009-09, Vol.24 (9), p.1724-1738
• Main Authors: Gao, Yuqiao, Liu, Li, Hu, Wenxuan
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemistry; Pollution, environment geology
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2009.05.002

The CO 2 gas reservoir sandstones in the Hailaer Basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of CO 2. The origins of dawsonite and CO 2 in these sandstones were studied by petrographic and isotopic analysis. According to the paragenetic sequence of the sandstones, dawsonite grew later than CO 2 charging at 110–85 Ma. The dawsonite δ 18O value is 7.4‰ (SMOW), and the calculated δ 18O values of the water present during dawsonite growth are from −11.4‰ to −9.2‰ (SMOW). This, combined with the NaHCO 3-dominated water linked to dawsonite growth, suggests meteoric water being responsible for dawsonite growth. The δ 13C values of gas phase CO 2 and the ratios of 3He/ 4He of the associated He suggest a mantle magmatic origin of CO 2-rich natural gas in Hailaer basin. Dawsonite δ 13C values are −5.3‰ to −1.5‰ (average −3.4‰), and the calculated δ 13C values of CO 2 gas in isotopic equilibrium with dawsonite are −11.4‰ to −7.3‰. These C isotopic values are ambiguous for the dawsonite C source. From the geological context, the timing of events, together with formation water conditions for dawsonite growth, dawsonite possibly grew in meteoric-derived water, atmospherically-derived CO 2 maybe, or at least the dominant, C source for dawsonite. It seems that there are few relationships between dawsonite and the modern gas phase of CO 2 in the Hailaer basin.