The Vaughton Siltstone of the northern McArthur Basin: preliminary data and issues related to assessing its potential as a petroleum source rock

Abstract

The Vaughton Siltstone BLUE MUD BAY is a recessive carbonaceous shale unit of the Balma Group (McArthur Basin). Its mineralogy bears similarity to unconventional self-sourcing petroleum shales seen elsewhere in the McArthur Basin. A number of samples from weathered exposures of this formation were analysed in order to assess their hydrocarbon potential. Analyses consisted of X-ray diffraction, shale rock properties, total organic carbon content, programmed pyrolysis, CHONS elemental kerogen content, organic petrography, and gas chromatography. Initial results indicate that petroleum generation has occurred, but very little petroleum has been retained such that the remaining hydrocarbon generative potential is considered negligible. The presence of bitumen within the samples indicates that thermal maturation has occurred, possibly from burial of the siltstone or from exposure to hydrothermal fluids. However, the use of weathered samples, exposed to atmospheric levels of oxygen and large volumes of meteoric water, creates uncertainty within the results; therefore sub-surface samples of fresh material would be required to determine the true petroleum potential.