The non-marine Lower Triassic Rewan Group in the Bowen Basin, Australia, is mainly composed of lithic arenites containing high proportions of volcanic rock fragments. Sublitharenites are also present. The arenites are cemented by abundant authigenic quartz, carbonates and clay minerals. Three separate lithostratigraphic intervals can be identified: a conglomeratic unit at the base; a sequence dominated by lithic arenites in the middle; and a section dominated by sub-litharenites at the top. Petrographically, the sandstones can be divided into a facies whose quartz content is greater than 75% on a QFR diagram; and a labile or lithic facies which contains less than 75% quartz. There is a progressive change in clay mineral assemblage from one petrofacies to the other. The volcanic fragments have undergone rapid diagenetic alteration under low temperatures and pressures. Alteration started with pore-space reduction by compaction and was followed by pore-fill cementation. Solution at depth, however, has caused secondary porosity to develop. Differences in clay mineralogy and in the overall proportion of clay within the Rewan Group can be explained by differences in permeability and fluid flux, with high permeabilities occurring in the conglomeratic and sublitharenitic intervals. Porosity is best developed where early silicification has enhanced grain support and has minimised the effects of later compaction, and where clay minerals have been leached.