δ13C of polycyclic aromatic hydrocarbons to establish the facies variations in a fluvial deltaic Triassic record (Dampier sub-Basin, Western Australia)

Abstract

The δ13C of polycyclic aromatic hydrocarbons (PAHs) was measured in a series of Triassic and Jurassic source rocks from the Dampier sub-Basin, Carnarvon Basin, North West Shelf of Australia. These sequences correspond to fluvial deltaic systems which integrate the Mungaroo, Brigadier and Legendre Formations, and the organic matter has been assigned as mixed terrigenous/marine material. The relative abundance of the PAHs was plotted against the difference between δ13C values of 1,3,6,7-tetramethylnaphthalene (TeMN) and each PAH. We demonstrated here that samples plotting below 0 for Δ13C (Combustion Marker-1,3,6,7 TeMN) are related to delta-plain/front-deltaic facies or coaly fluvial deltaic facies (e.g. samples from the Mungaroo Formation - North Rankin-5, Goodwyn-9 and Goodwyn-5 wells) whereas the positive region for Δ13C (Combustion Marker-1,3,6,7 TeMN) is assigned to transitional facies deposited under an estuarine/lagoonal environment with a high sapropelic contribution (Brigadier Formation) and marginal marine environment (Legendre Formation). A similar separation for the samples was obtained with phenanthrene and other PAHs. The δ13C of PAHs in combination with their distributions can be used to establish the facies type i.e. delta-plain/front-deltaic from estuarine/lagoonal in a dominantly fluvial deltaic record. Our research provides new tools to take into account for further applications in fluid-source rock correlation studies which represent the main challenge in assessing petroleum systems in the sub-Basin.