黔南坳陷下寒武统烃源岩地球化学特征及成因

为明确黔南坳陷下寒武统烃源岩地球化学特征及成因,采用岩石热解、GC、GC—MS等方法对3个典型剖面样品进行了系统分析。结果表明：黔南坳陷下寒武统黑色岩系为一套区域性海相优质烃源岩,厚约50～150 m;烃源岩TOC值为0.13%～15.40%,平均3.31%（n=169）;烃源岩干酪根δ13C值为-35.79‰～-29.88‰,平均-32.85‰（n=35）,显微组分主要为腐泥组;烃源岩干酪根海相镜质体反射率值为1.95%～3.96%,其等效镜质体反射率值为2.02%～3.47%;烃源岩饱和烃正构烷烃分布多为单峰形,主峰碳多为C22,C30藿烷和C27规则甾烷含量高,规则甾烷多为C27〉C29

Geochemical Characteristics and Origins of the Lower Cambrian Source Rocks from the Southern Guizhou Depression,SW China

The Lower Cambrian source rock samples from three typical profiles in the southern Guizhou Depression were analyzed for TOC values,δ13C values,Tmax temperatures,potential generation,and biomarkers using Rock-Eval,GC,GC-MS to elucidate the geochemical characteristics and its origin.The results show that the Lower Cambrian black shales in the southern Guizhou Depression are regional marine excellent source rocks with depth of 50-150m,and have the TOC values of 0.13%-15.40%,average 3.31%(n=169);the kerogens of the source rocks have the δ13C values of-35.79‰——29.88‰,average-32.85‰(n=35),and the kerogen macerals are mainly sapropelinites;the values of the marine vitrinite reflectance of the kerogens are 1.95%-3.96%,and the values of the equivalent vitrinite reflectance are 2.02%-3.47%;the distribution shapes of the n-alkanes are mainly single peak,and the maximum peak carbon are mainly C22,the C30 hopane and C27ααα20R regular sterane are abundant,the regular steranes are mainly C27>C29>C28,the Pr/Ph values are 0.27-0.62,the source rocks have relative high abundance of gammacerane and dibenzothiophene,the OEP values are 0.82-1.11,C31 homohopane 22S/(22S+22R) have values of 0.56-0.63,average 0.59;the source rocks are generally characterized by enrichment in light REE,Ba,Mo,V and U element,relative strong negative anomaly of Ce element,relative strong positive anomaly of Eu element and relative high ratio of U/Th.In summary,the Lower Cambrian marine source rocks in the southern Guizhou Depression have a wide distribution with a thickness of from tens of meters to hundreds of meters,the source rocks have high TOC values,are excellent for organic matter type,and have a post-maturity.It is the product which is jointly controlled by high paleo-productivity and anoxic environment.It can provide abundant organic matter for hydrocarbon generation in the southern Guizhou Depression.