Carbonate, organic carbon and nitrogen, bitumen and rock-eval pyrolysis at DSDP Leg 79 Holes@en

The lipids and kerogens of 15 sediment samples from Site 547 (ranging from Pleistocene to Early Jurassic/Triassic) and 4 from Site 545 (Cretaceous) have been analyzed. A strong terrestrial contribution of organic matter was found, and significant autochthonous inputs were also present, especially at Site 545. Both strongly reduced and highly oxidized sediments have been found in the Cenozoic and Jurassic samples of Site 547. On the contrary, all the Cretaceous sections of Sites 547 and 545 are anoxic. Sediments from anoxic paleoenvironments are immature and have a high content of sterenes, diasterenes, steradienes, hopenes, and ßß hopanes. Samples from oxic paleoenvironments are mainly mature and their content of hopenes and steriod structures is below the detection level. Nevertheless, their hopane distributions have the immature ßß homologs as the predominant molecular markers. For Site 545 the most abundant molecular markers are ring A monoaromatic steranes, and their presence is attributed to microbial and chemical transformations during early diagenesis.对547站位（Site 547）的15个沉积物样品（时代跨度为更新世至早侏罗世/三叠纪），以及545站位（Site 545）的4个沉积物样品（时代为白垩纪）中的脂类（lipids）与干酪根（kerogens）开展了分析测试。研究发现有机质存在显著的陆源贡献，同时也存在明显的原地输入特征，该特征在545站位尤为突出。在547站位的新生代与侏罗纪样品中，同时发现了强还原与强氧化的沉积物；与之相反，547站位与545站位的所有白垩纪地层均处于缺氧（anoxic）古环境中。缺氧古环境下的沉积物多处于未成熟状态，且富含甾烯（sterenes）、双甾烯（diasterenes）、甾二烯（steradienes）、藿烯（hopenes）及ββ-藿烷（ßß hopanes）。富氧（oxic）古环境下的样品则多已成熟，其藿烯与甾类结构的含量低于检测限；不过，其藿烷分布仍以未成熟的ββ同系物作为主要分子标志物（molecular markers）。对于545站位而言，丰度最高的分子标志物为A环单芳甾烷（ring A monoaromatic steranes），该类物质的存在被归因于早成岩作用（early diagenesis）过程中的微生物与化学转化作用。