Elemental and isotope compositions of lipids, kerogens and asphaltenes from samples of DSDP Hole 41-368

The thermal effects of three (one major and two minor) Miocene diabase intrusions on Cretaceous black shales from DSDP site 41-368 have been analyzed. A concentration gradient was observed, especially for the hydrocarbons, decreasing towards the major intrusion and between the three sills. The thermally-altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally-derived pristane over phytane. whereas, the unaltered sediments contained no elemental sulfur, and more phytane than pristane. A maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill. Two classes of molecular markers were present in this bitumen suite. The first was sesqui-, di- and triterpenoids and steranes. which could be correlated with both terrigenous and autochthonous sources. They were geologically mature and showed no significant changes due to the thermal stress. The second class was found in the altered samples, which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds. These compounds were derived from pyrolytic reactions during the thermal event.
Kerogen was isolated from all of these samples, but only traces of humic substances were present. The H/C, N/C, d13C, d34S and dD all exhibit the expected effects of thermal stress. The kerogen becomes more aromatized and richer in 13C, 34S and D in the proximity of and between the sills. Maturation trends were also measured by the vitrinite reflectance and electron spin resonance, where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity. The effects of in situ thermal stress on the organic-rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills.

本研究针对深海钻探计划（Deep Sea Drilling Project, DSDP）41-368站位的白垩系黑色页岩（Cretaceous black shales），分析了3处中新世辉绿岩侵入体（Miocene diabase intrusions，1处主侵入体、2处次侵入体）对其产生的热效应。

研究观测到浓度梯度现象，尤以烃类（hydrocarbons）最为显著：其浓度向主侵入体方向以及三处岩床（sills）之间逐渐降低。岩床邻近区域及岩床间的热变质样品中检出单质硫（elemental sulfur），且热成因姥鲛烷（pristane）含量高于植烷（phytane）；而未受变质的沉积物则不含单质硫，且植烷含量多于姥鲛烷。

在主岩床下方7米深度处，可萃取烃类（extractable hydrocarbons）的产率达到峰值。该沥青族组分（bitumen suite）包含两类分子标志物：第一类为倍半萜、二萜、三萜类化合物（sesqui-, di- and triterpenoids）及甾烷（steranes），其来源可同时关联陆源成因与原地成因沉积体系；该类化合物已达到地质成熟度，且未因热应力出现显著变化。

第二类分子标志物仅见于变质样品中，包含低烷基取代的多环芳烃（polynuclear aromatic hydrocarbons）以及硫、氧杂环芳香化合物（sulfur and oxygen heterocyclic aromatic compounds），这类物质源自热事件过程中的热解反应（pyrolytic reactions）。

所有样品均成功分离得到干酪根（Kerogen），但仅检出微量腐殖物质（humic substances）。样品的H/C、N/C、δ¹³C、δ³⁴S及δD值均表现出热应力带来的预期变化：在岩床邻近区域及岩床之间，干酪根的芳构化程度更高，且¹³C、³⁴S及D的富集程度也更高。

研究还通过镜质体反射率（vitrinite reflectance）与电子自旋共振（electron spin resonance）测试得到成熟度变化趋势，其中热应力与围岩（country rock）温度升高及芳构化程度提升呈显著相关。

原位热应力对富有机质页岩（organic-rich shales）的影响，最终导致岩床附近区域生成并排出了石油类物质（petroliferous material）。