Littoral talus Breccia and probable beach rock from the Viséan of the Bonaparte Gulf Basin

Abstract

In the southwestern Bonaparte Gulf Basin, a pebbly sandstone and an overlying dolomite breccia (together called the Waggon Creek Breccia) mantle a partly exhumed late Tournaisian and early Viséan surface. The sandstone contains pebbles of metaquartzite and quartz, and the breccia consists of angular blocks of dolomite up to 30 ft (9 m.) long, and rounded pebbles and boulders of quartz and metaquartzite, in a sandy dolomite matrix. Marine fossils indicate a Visean age. The pebbly sandstone is probably beach rock, and the overlying breccia is a littoral talus breccia probably formed by the isolating and undermining by the sea of beds of dolomite in the otherwise soft Cockatoo Formation. Many coarse breccias are related to the relief along faults, whether actual or postulated; the Waggon Creek Breccia probably owes its coarse texture to sedimentary and erosional processes only, and its description here may help in the recognition of similar deposits elsewhere. A similar breccia was deposited nearby during a brief marine incursion in the mid‐Tournaisian. In the late Tournaisian and early Viséan, the terrain of the Waggon Creek area was essentially the same as that of the present day, the relief exceeded 500 ft (150 m.), and the climate was warm.