四川盆地海、陆相烃源岩有机质稳定碳同位素组成变化及其地球化学意义

采用质谱和色谱-同位素质谱技术，测定了500余个干酪根及饱和烃、芳烃组份、正构烷烃的δ13C值，以此揭示了四川盆地海、陆相烃源岩有机碳同位素组成随地质时代的变化特点及其在高成熟阶段的演化特征，并结合其他相关分析资料，应用碳同位素剖析了不同类型海、陆相烃源岩的有机质生源及沉积环境。研究结果表明，该盆地从震旦系灯影组到中三叠统雷口坡组的海相地层中，干酪根的碳同位素组成随层位变新呈逐渐变重的趋势，可能的原因之一是浮游植物的进化作用；而上三叠统须家河组至中侏罗统千佛崖组的陆相有机质碳同位素组成则有反向的年代变化，主要与生源构成和沉积环境性质有关。这些海、陆相烃源岩的有机源难以用干酪根δ13C值进行区分，而可用饱和烃与芳烃组份的δ13C及其CV值来区别。海洋和湖泊不同沉积相带烃源岩的干酪根具有明显不同的δ13C值，结合其他相关资料可识别其有机质来源。煤系地层中煤与泥岩在干酪根碳同位素组成上没有可区分性，而两者有不同的正构烷烃碳同位素分布曲线。从成熟晚期到高-过成熟阶段，海、陆相干酪根的碳同位素均变重1~2‰，煤系泥岩的正构烷烃碳同位素分布曲线由负向线型分布向平直型演变。这些碳同位素的变化特征为油气源对比和烃源识别提供了依据。

Compositional Variations and Geochemical Significances of Stable Carbon I-sotope for Organic Matters from Marine and Terrestrial Source Rocks in Sichuan Basin

Over 500 kerogens as well selected saturate and aromatic fractions and n-alkanes from various age source rocks in the Sichuan basin were analyzed using MS and GC-ir-MS forδ13 C ratios, to characterize the age-trend in or-ganic carbon isotopic composition in marine and terrestrial sediments and their thermal evolution during over-mature stage. Moreover, different kind of marine and terrestrial source rocks with respect to their biological organic sources were distinguished using carbon isotopes in combination with other analytical data. The results indicate the kerogens from marine sediments in Sinian Dengying to middle Triassic Leikoupo Formations in this basin show a trend toward i-sotopically heavy values with decreasing age, possibly due to biological evolution. Whereas, a reversal isotopic-age trend for the terrigenous organic carbon is observed in upper Triassic Xujiahe to middle Jurassic Qingfoyan Formations and is considered to be dependent of biological source and sedimentary environment. The organic inputs of marine and terrestrial source rocks cannot be differentiated using the carbon isotopic ratios of kerogen, however, it can be distin-guished byδ13 C values of saturated and aromatic fractions and CV values. The marine and lacustrine source rocks with different facies are of obviously varying δ13 C values of kerogens, thus the isotopic ratio, combined with additional re-late-source data, can be acted as an indicator for their organic source. Coal and mudstone in coal-bearing strata is not distinguishable for their kerogen carbon isotopes, but has different profiles of n-alkane isotopes with more negative val-ues in mudstone related to coal. The marine ( type-Ⅱ) and terrigenous ( type-Ⅲ) kerogens both continuously become isotopically enriched in 13 C by 1‰~2‰ with maturation during high-over maturity. The negatively sloping curve of carbon isotope for individual n-alkanes from coaly source rock at mature stage is transferred into a flat one at high ma-turity. These variations in carbon isotope compositions are helpful for oil & gas-rock correlation and hydrocarbon source identification.