中上扬子北缘中古生界海相烃源岩特征

中上扬子北缘中古生界海相层系有机地球化学剖面的研究表明,中古生界海相层系烃源岩主要发育于下寒武统、上奥陶统五峰—下志留统龙马溪组底部和二叠系。其中下古生界烃源岩以泥质岩为主,有机质丰度高,有机质类型好,多属好—最好的烃源岩;上古生界(P)烃源岩以碳酸盐岩为主,泥质岩为辅,前者有机碳一般<1%,多属较好的烃源岩,后者有机质丰度高,多属好—最好的烃源岩;二叠系碳酸盐岩和泥质烃源岩有机质类型复杂多样,以Ⅱ₁型为主。3套烃源岩热演化程度普遍较高,等效镜质体反射率R_o一般>2.0%,区内油气结构以天然气为主。烃源岩可溶有机质有机地球化学特征研究表明,下古生界烃源岩正构烷烃呈单前峰型,而二叠系烃源岩正构烷烃有3种类型。在甾、萜烷生物标志化合物方面,二叠系烃源岩以较低的C₂₁三环萜烷/C₂₃三环萜烷、C₂₇规则甾烷/C₂₈₊₂₉规则甾烷等为显著特征而区别于下寒武统烃源岩,五峰组—龙马溪组烃源岩则介于其间。 

CHARACTERISTICS OF MIDDLE PALAEOZOIC MARINE SOURCE ROCK IN THE NORTH MARGIN OF MIDDLE AND UPPER YANGTZE REGION

Organic geochemical researches on the Middle Palaeozoic marine profiles in the north margin of Middle and Upper Yangtze region show that the Middle Palaeozoic marine source rock mainly developed in Lower Cambrian,the bottom of Upper Ordovician Wufeng-Lower Silurian Longmaxi Formation and Permian.The Lower Palaeozoic source rock is mainly argillaceous rock with high organic abundance and is considered as the best source rock.The Upper Palaeozoic source rock is given first place to carbonate rock while making argillaceous rock subsidiary.The former belongs under the relatively good source rock with organic carbon usually being less than 1%.The latter belongs in the best source rock with high organic abundance.Types of organic matter in Permian carbonate and argillaceous source rock are many and complex with type Ⅱ₁ being of primacy.The extent of thermal evolution of these three sets of source rock is generally high with equivalent vitrinite reflectance usually being more than 2.0%.Gas is dominant in Middle and Upper Yangtze region.Research on the organic geochemical features of soluble organic matter in source rock shows that the normal alkanes in Lower Palaeozoic source rock are of frantal monopeak while that in Permian source rock hawing three types.The ratios of C₂₁ tricyclic terpans to C₂₃ tricyclic terpans and C₂₇ regular steranes to C₂₈₊₂₉ regular steranes are low in Permian source rock while those in Lower Cambrian source rock being high.In Wufeng-Longmaxi Formation source rock,the above-mentioned ratios are between the both.