Thermal alteration of Cretaceous black shale from the Eastern Atlantic. III: Laboratory simulations

Abstract

Laboratory thermal alteration (pyrolysis) experiments were carried out on composited Cretaceous black shale samples from DSDP Hole 368. Dried rock samples (low water-rock ratio) were heated in an inert atmosphere in the range of 250–500°C and the resultant bitumen and kerogen concentrates were characterized. Pyrobitumen forms initially (250°C), then major hydrocarbon generation occurs from 300–360°C and oxygenated products ( e.g. alkanoic acids) have a maximum yield at 330–360°C with minor generation to 500°C. Dealkylation of the aromatic hydrocarbons to the parent polynuclear aromatic hydrocarbons occurs above 400°C. The kerogens become more aromatic with increasing pyrolysis temperature (atomic H/C decreases from 1.2 to 0.5 and vitrinite reflectance increases to 3%). The temperature ranges of pyrobitumen, bitumen, and PAH formation in dry pyrolysis experiments are of utility in correlating with field data on ore genesis.