Organic geochemical studies of DSDP Leg 64 Holes@en

Twenty-six core samples from Leg 64, Holes 474, 474A, 477, 478, 479, and 481A in the Gulf of California, were provided by the Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES) Advisory Panel on Organic Geochemistry for analysis. The high heat flow characteristic of the basin provides an opportunity to study the effect of temperature on the diagenesis of organic matter. The contents and carbon isotope compositions of the organic matter and bitumen fractions of different polarity, isoprenoid and normal alkane distributions, and the nature of tetrapyrrole pigments were studied. Relative contents of hydrocarbons and bitumens depend on the thermal history of the deposits. Among other criteria, the nature and content of tetrapyrrole pigments appear to be most sensitive to thermal stress. Whereas only chlorins are present in the immature samples, porphyrins, including VO-porphyrins, appear in the thermally altered deposits, despite the shallow burial depth. Alkane distributions in thermally changed samples are characterized by low values of phytane to 2-C18 ratios and an odd/even carbon preference index close to unity. The thermally altered samples show unusual carbon isotope distributions of the bitumen fractions. […]本研究使用的26块岩心样品取自加利福尼亚湾第64航次的474、474A、477、478、479及481A孔，由深海钻探联合海洋机构（Joint Oceanographic Institutions for Deep Earth Sampling，JOIDES）有机地球化学咨询专家组提供用于分析。该盆地具有高热流特征，为探究温度对有机质成岩作用的影响提供了理想契机。研究内容涵盖有机质与不同极性沥青组分的含量及碳同位素组成、类异戊二烯烷烃与正构烷烃分布特征，以及四吡咯色素（tetrapyrrole pigments）的性质。烃类与沥青的相对含量取决于沉积地层的热演化历史。在诸多判别指标中，四吡咯色素的性质与含量对热应力的响应最为敏感。未成熟样品中仅检出氯啉（chlorins），而尽管埋藏深度较浅，经热改造的沉积地层中却出现了包括钒卟啉（VO-porphyrins）在内的卟啉类化合物。经热改造的样品中，烷烃分布表现为植烷与2-C18烷烃比值偏低，且碳数奇偶优势指数接近1。经热改造的样品呈现出异常的沥青组分碳同位素分布特征。[…]