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. […]