Adavale Basin

Basin Details and Geological Overview

The Early Devonian to Early Carboniferous Adavale Basin of central Queensland is entirely subsurface, occupies about 60 000km² and contains about 8000m of sediments and minor volcanics. Over 20 petroleum wells have been drilled in the basin. The basin was initiated in the late Early Devonian (Emsian) as a rifted back-arc basin west of a volcanic arc subduction zone complex. The basal unit, which comprises volcanics, volcaniclastics and continental redbeds was deposited during this rifting phase. As extension continued, a widespread Emsian to Eifelian fluvio-deltaic complex was deposited, followed by an Eifelian to early Givetian unit, comprising marine shales in the east and fluvio-deltaic and marginal marine sandstones in the west.

This was followed by a period of restricted clastic input with deposition of shallow water carbonates. As convergence began from the east, tectonic uplift barred the basin, with concomitant deposition of extensive evaporites. Continued compression from the east was accompanied by major tectonic uplift of the Anakie-Nebine volcanic arc complex. This provided the source for the final phase of sedimentation in the basin, a succession of interbedded shales and sandstones followed by a syntectonic mollasse-type, coarse siliciclastic succession. Convergence continued until the Middle Carboniferous, with the development of a series of thrust faults. Uplift and erosion continued well into the Late Carboniferous with only the remnants of what once was a more extensive basin being preserved. Deposition of the overlying Galilee Basin commenced in the Late Carboniferous.

The basin produces wet gas from the fault bounded, anticlinal trap of the Gilmore field, which is piped to Barcaldine and to the Ballera-Brisbane pipeline. The wet gas and associated oils are from a Devonian marine source which generated in the Carboniferous, and dry gas from a subsequent heating of those same source rocks which began in the Cretaceous.

Key References