A tide- and wave-moulded shelf sequence from the Permian of the southwest Bowen Basin, Queensland, Australia

Abstract

The Early Permian Staircase Sandstone Member of the Cattle Creek Formation forms part of the Permo-Triassic basin fill in the Denison Trough (southwest Bowen Basin). The interval is interpreted as the deposits of a wave- and tide-influenced delta because of its interbedded lithological character, alternation of marine and non-marine strata, bipolar palaeocurrent distribution and assemblage of preserved sedimentary structures. The Staircase Sandstone delta prograded eastward into the basin from the northwestern margin, passing distally into progressively more offshore facies. Three component facies are recognized within the inner shelf facies association; facies 1 — pebble conglomerate, facies 2 — sandstone, and facies 3 — siltstone/very fine grained sandstone. The presence of amalgamated hummocky cross-stratification and winnowed, top-surface pebble lags attests to the influence of storms on sediment deposition, while the palaeocurrent distribution demonstrates the operation of tides. Palaeohydraulic calculations on wave-generated structures suggest that during deposition of the Staircase Sandstone Member, the southern Bowen Basin was 250–300 km wide. Despite this narrow, elongate and hence restricted geometry, the basin was subjected to both modest (?micro) tidal circulation and the influence of storm-generated waves and currents.