Diagenesis of organic matter and fine clay minerals: a comparative study

• Main Authors: Snowdon, L.R(http://viaf.org/viaf/244090245), P. R. Gunther(), T. G. Powell(), Φωσκολος Αντωνης(http://users.isc.tuc.gr/~afoskolos), Foskolos Antonis(http://users.isc.tuc.gr/~afoskolos)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2015
• Subjects: Northwest Territories
• Online Access: http://purl.tuc.gr/dl/dias/7F74544D-71FC-47EB-94CB-CAC0638340B4; http://www.sciencedirect.com/science/article/pii/0016703778901138 10.1016/0016-7037(78)90113-8

Summarization: A geochemical study has been made of fine clay minerals and organic matter in subsurface shale samples from the Canadian Northwest Territories. The mixed layer clays comprise smectite-vermiculite-illite but are transformed during thermal diagenesis to a pseudo-quaternary system (smectitevermiculite-illite-chlorite) by incorporation of amorphous inorganic material. The first clay dehydration occurs prior to hydrocarbon generation and is accompanied by adsorption of K+ and substitution of Al3+ for Si4+ in the clay lattice. Vermiculite is an intermediary in the transformation of smectite to illite and in the presence of Ca2+ ions delays the second dehydration step to the zone where cracking of liquid hydrocarbons to gas occurs. Hydrocarbon generation commences at a vitrinite reflectance level of ≅ 0.5% R0 maximum in both amorphous and woody-herbaceous organic matter but does not reach a significant level in the latter case until reflectance levels of 0.7% R0 maximum. The pristane to phytane ratio and proportion of n-alkanes and acyclic isoprenoids increase during hydrocarbon generation from woody-herbaceous organic matter. Anomalous hydrocarbon yields from certain samples are attributed to high concentrations of plant resins. Destructions of liquid hydrocarbons by cracking commences at a reflectance level of 1.0% R0 maximum and is essentially complete by a reflectance level of 1.4% R0 maximum. The proportion of n-alkanes in the saturates decreases during cracking of the liquid hydrocarbons. Presented on: Geochimica et Cosmochimica Acta