9 drillcore calcareous siltstone samples of the Early Cambrian Moonan Formation taken from Port Julia 1A mineral exploration well were submitted for determination of that stratigraphic unit's geothermal maturity with respect to hydrocarbon generation, plus its organic richness and hydrocarbon source potential. The analytical results have allowed the conclusion that this formation is for the most part organically lean (mean total organic carbon = 0.12-1.50%) and contains gas-prone Type IV kerogen; its extractable triaromatic hydrocarbons give an estimated level of thermal maturity (calculated vitrinite reflectance = 1.10 to 1.24%) which corresponds to the gas-condensate phase of hydrocarbon generation.