The organic geochemistry of the Mesoproterozoic Velkerri Formation and investigations into syngenicity and indigeneity of hydrocarbons using slice experiments

Abstract

The usefulness of Precambrian hydrocarbons, in particular biomarkers, relies entirely upon both their syngenicity and indigeneity, or rather whether or not they are representative of the same time period and area as the host rock. Due to both age and typically low total organic carbon content however, Precambrian basins are susceptible to hydrocarbon overprinting due to contamination.

This study investigates the presence and nature of hydrocarbon signatures in quarter core slices (from the outside to inside of the core) from the 1.4 billion year old Velkerri Formation, McArthur Basin and assesses the likelihood of the syngenicity and indigeneity of the analysed hydrocarbons. Each slice was crushed, solvent extracted, silica column fractionated and analysed using a Leco two dimensional gas chromatograph (Agilent 7890A) operating in one dimension, coupled to a Pegasus time-of-flight-mass spectrometer (GCxGC-ToFMS). Furthermore, identified hydrocarbons are used to clarify both the thermal maturity and source characteristics of the middle Velkerri Formation.