Organic petrology and source rock potential of sediments in the Eromanga Basin, South Australia

Cuttings and cores from the Poolowanna 1 well, Eromanga Basin, South Australia (in which oil was discovered in Lower Jurassic reservoirs) and the Macumba 1 well (no oil) have been analyzed petrographically to assess the nature of the coals and dispersed organic matter present. The Jurassic and Cretaceous coals have medium to high vitrinite contents, low to relatively high exinite, and medium to low inertinite contents. The dispersed organic matter has comparatively less vitrinite, more exinite and/or more inertinite than the associated coals. The microlithotype compositions of the coals indicate that the original vegetation was largely woody in character and was buried before much oxidation had occurred.The Jurassic sediments contain up to 2% dispersed organic matter by volume, 0–75% of which is exinite, including alginite. Vitrinite reflectances range from 0.5 to 0.7%. Where sufficiently mature, the Jurassic sediments are good potential source rocks for hydrocarbons.Statistical testing of the analytical results for the Jurassic Poolowanna Formation using Kendall's τ as a measure of dependence shows that there is a significant association between the macerals in coal and dispersed organic matter. The ratio of exinite to inertinite in dispersed organic matter is reasonably well predicted by the corresponding ratio in the associated coal.