Investigations of Cretaceous and Tertiary kerogens in sediments of ODP Leg 113 holes

Seventy-one samples from nine sites were analyzed for total organic carbon (TOC). Fifty-six samples, containing 0.2% or more TOC, were evaluated by Rock-Eval to assess the nature of their kerogen and its petroleum source potential. Visual kerogen studies were carried out. Petroleum potential was encountered only in Valanginian calcareous claystones at Hole 692B close to the margin of Dronning Maud Land. A section of 44.7 m was penetrated. The unit possesses a revised mean TOC of 9.8% and petroleum potential of 43.2 kg/Mg, relatively high values in comparison to other Cretaceous anoxic oceanic sections and the totality of petroleum source rocks. At Sites 689 and 690, extremely low TOC levels, mean 0.07%, preclude kerogen analysis. Kerogens in Eocene to Pliocene sediments of the central and western Weddell Sea (Sites 694, 695, 696, and 697) are similar everywhere, largely comprising brown to black, granular, amorphous material of high rank, and generally possessing several reflectance populations of vitrinite particles. The latter are interpreted as indicative of the recycling of sediments of a variety of levels of thermal maturity.

本研究对采自9个站位的71件样品开展了总有机碳（total organic carbon, TOC）测试分析。其中总有机碳含量不低于0.2%的56件样品，通过岩石热解仪（Rock-Eval）进行测试，以评价其干酪根（kerogen）类型与油气源岩潜力，并同步开展了干酪根镜下鉴定工作。仅在毗邻毛德皇后地（Dronning Maud Land）的692B钻孔的凡兰吟期（Valanginian）钙质黏土岩中发现了油气潜力。该沉积段钻遇厚度达44.7米，经修正后的总有机碳平均含量为9.8%，油气潜力为43.2 kg/Mg，相较于其他白垩纪缺氧海洋沉积段以及所有油气源岩，该值均处于较高水平。在689和690两个站位，总有机碳含量极低，平均仅为0.07%，无法开展干酪根分析。威德尔海（Weddell Sea）中西部始新世至上新世沉积物（对应694、695、696及697站位）中的干酪根特征整体均一，主要由高成熟度的棕黑色颗粒状无定形物质构成，且镜质体（vitrinite）颗粒普遍存在多组反射率分布特征。上述镜质体反射率特征被认为指示了不同热成熟度级别沉积物的再循环作用。