为明确黔南坳陷不同层位油苗来源,在广泛采集不同层位烃源岩、油苗样品的基础上,采用GC、GC-MS及GC-IRMS等方法对其碳、硫同位素及生物标志物特征进行系统分析,进而开展了油源对比.结果表明:油苗的δ13C值为-33.04‰～-31.63‰,平均-32.26‰(n=18)；δ34S值为+16.06‰～+23.06‰,平均+18.99‰(n=4)；油苗遭受不同程度生物降解,常规甾、萜烷面貌特征差异较大,但普遍含有较丰富的三环萜烷、伽玛蜡烷、三芳甾烷、芳基类异戊二烯烃、惹烯和硫芴；C25三环萜烷/C24四环萜烷值、二苯并噻吩/菲与Pr/Ph相关图表明油苗为典型海相原油；Ts/(Ts +Tm)、C29甾烷20S/(20S+ 20R)及甲基菲指数等均表明油苗为成熟-高熟原油.研究区下寒武统牛蹄塘组黑色泥岩干酪根δ13C值为-35.79‰～-29.88‰,平均-32.85‰(n=35),与油苗相关性良好,而泥盆系、石炭系和二叠系烃源岩δ13C值显著偏重,均大于-29‰；下寒武统牛蹄塘组黑色泥岩干酪根δ34S值为+ 14.78‰～+ 17.60‰,平均+16.32‰(n=4),与油苗具有很好的可比性,而下、中泥盆统黑色泥岩干酪根δ34S值分别为-9.10‰～-6.78‰和+0.63‰～ +7.93‰,二叠系煤系地层有机质δ34S值为-7.40‰～+4.00‰,均显著偏轻.此外,下寒武统黑色泥岩普遍含有较丰富的伽玛蜡烷、三芳甾烷、芳基类异戊二烯烃和惹烯,三芴系列中硫芴含量极高,其它几套黑色泥岩则不合或贫含三芳甾烷和惹烯,伽玛蜡烷和硫芴含量亦较低.综合认为油苗具相同来源,且均与研究区下寒武统黑色泥岩具有较好亲缘关系.%An oil-source rock correlation method based on carbon isotopes, sulfur isotopes and biomarkers is described for potential source rocks and oil seepages in the southern Guizhou Depression to elucidate the origins of oil seepages. The results show that the oil seepages have bulk δ13C values from -33. 04‰ to -31. 63‰, average -32. 26‰ (n = 18) , and have δ34S values from + 16. 06‰ to +23. 06‰, average +18. 99‰ ( n =4) ; the oil seepages are biodegraded with a varying degree, there are many differences in distribution of steranes and terpanes, but they are all relatively rich in tricyclic terpanes, gammacerane, triaromatic steroids, aryl isoprenoids, retene and dibenzothiophene; C25 tricyclic terpane to C24 tetracyclic terpane and the cross plot of dibenzothiophene to phenanthrene and pristane to phytane indicate that the oil seepages are marine origin petroleum; Ts/(Ts +Tm) , C29sterane20S/(20Srn+ 20R) and methylphenanthrene index all demonstrate that the oil seepages are mature to highly mature. The source rocks from the Lower Cambrian Niutitang Formation in the study area have bulk 5 Ckerogen values from -35. 79‰ to —29. 88‰, average -32. 85‰ ( n = 35) , and have δ34Skerogen values from + 14. 78‰ to + 17. 60‰, average + 16. 32‰ ( n =4) , they are well-correlated with those of oil seepages. However the source rocks from the Devonian, Carboniferous and Permian all show bulk 513Ckerogen values of more thanrn-29. 00‰, which are significantly heavier than those of oil seepages. The source rocks from the Lower Devonian, Middle Devonian and Permian show S34Skerogen values from -9. 10‰ to -6. 78‰, +0. 63‰ to + 7. 93‰, and -7. 40‰ to +4. 00‰, respectively, which are significantly lighter than those of oil seepages. Moreover, the source rocks from the Lower Cambrian are relatively rich in gammacerane, triaromatic steroids, aryl isoprenoids, retene and dibenzothiophene, whereas the other source rocks are absent or poor of triaromatic steroids and retene, and show lower abundance of gammacerane and dibenzothiophene. Thus it is demonstrated comprehensively that the oil seepages from the southern Guizhou Depression have the same origin, and are genetically linked to the source rocks of the Lower Cambrian.
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