川东南-湘西志留系砂岩胶结物碳、氧同位素特征

Carbon and Oxygen Isotope Geochemistry for Carbonate Cement of the Lower Silurian Xiaoheba Formation Sandstone in Southeast Sichuan-West Hunan

测试分析结果表明:川东南-湘西地区氧稳定同位素相对较轻,而碳同位素变化相较于氧同位素变化大,这种变化与水介质性质、古气候及沉积有机质来源量有关;研究区志留系小河坝组砂岩形成胶结物的孔隙流体与海相环境中保存下来的底水密切相关;碳酸盐胶结物中的碳来源于与甲烷细菌作用生成生物气有关的碳酸盐。

22 sandstone samples from the Silurian Xiaoheba Formation in southeast Sichuan and west Hunan are sampled. δ^13Cvalues for carbonate cement of sandstone in southeast Sichuan vary from-1.90‰ to 4.78‰ with average value of 1.42‰, while δ^13Cvalues in west Hunan vary from-2.67‰ to 4.95‰ with average value of 1.99‰. δ^18Ovalues for all the 22 samples are negative： δ^18Ovalues for those in southeast Sichuan range between-13.115‰ and-9.45‰ with average value of-11.41‰, while δ^18Ovalues for those in southeast Sichuan and west Hunan range between-12.96‰ and-10.14‰ with average value of-11.54‰. These values indicate that carbon of the carbonate cement was derived from bacterium-derived methane.