The Jurassic and Lower Cretaceous sandstones of the Eromanga Basin in New South Wales can be divided into quartzose and volcanolithic petrofacies. The latter comprises sandstones of the Cadna-owie and Wallumbilla Formations which are predominantly volcanic-orogen-sourced lacustrine-to-paralic and shallow-marine deposits; the quartzose petrofacies comprises the craton-sourced fluvial Hooray Sandstone, the correlative fluvial and lacustrine Mooga Formation, and subordinate basal and other intercalated phases of the overlying Cadna-owie Formation. The diagenetic overprints in the sandstones include physical compaction, clay infiltration, cementation, and the dissolution and replacement of labile grains. The authigenic minerals in the chemically reactive volcanolithic sandstones are, in temporal order of appearance: syndepositional-glauconie, pyrite, sporadic carbonate, smectite (including nontronite, smectite and mixed-layers mectite/chlorite), zeolite (heulandite and mordenite), and kaolinite ; and in the chemically stable quartzose sandstones, the authigenic minerals are, in order of appearance: quartz (phase I), sporadic carbonate, accessory chlorite, and quartz (phase II) and kaolinite. Cutans of mechanically infiltrated clay and/or thin authigenic chlorite grain-coatings constitute early diagenetic overprints in the quartzose sandstones of the Hooray Sandstone/ Mooga Formation and the Cadna-owie Formation, and thereby minimised subsequent reduction of the substantial primary porosity of these rocks by precluding pervasive quartz-vergrowth cementation. The present-day excellent aquifer function of these quartzose sandstones is due largely to this circumstance, perhaps augmented by a history of geochemical pore-fluid conditions that were generally unfavourable for the volumetrically large-scale precipitation of either silica or carbonate. The volcanolithic sandstones average 35 % core porosity and 125 md permeability. Micropores constitute the predominant pore-type in these rocks and, where macropores are present, they comprise both isolated primary intergranular and secondary grain-dissolution pores, the origin of the latter likely being related to the interaction between labile sand grains and pore-fluid derived in part from intercalated organic-rich mudrocks. The quartzose sandstone has 29% (mean) core porosity and 676 md (mean) permeability; and the pore-types are mainly primary intergranular pores, and accessory intragranular grain-dissolution pores (mostly within feldspar grains). The development of the secondary-dissolution pores in the quartzose sandstone manifests the influence of meteoric (artesian) water and is a late diagenetic event. The distribution patterns of porosity- permeability of the lithic and quartzose sandstones correlate well with the respective depositional environments of these rocks as manifested by their bulk lithofacies characteristics.
