THE PLEASANT CREEK ARCH, ADAVALE BASIN, A MID DEVONIAN TO MID CARBONIFEROUS THRUST SYSTEM

Abstract

Interpretation of recently acquired multifold seismic data has led to a reappraisal of the structural evolution of the Adavale Basin with particular reference to the Pleasant Creek Arch.

The Basin initially formed as a back arc basin to the west of the Anakie/Nebine volcanic arc. Three stages of tectonic evolution are recognised; rifting, extension and convergence. The Pleasant Creek Arch represents a foreland fold belt cratonward of the major convergent margin deformational zone.

The model proposed for the development of the Pleasant Creek Arch is a buried to weakly emergent foreland thrust system modified by Late Carboniferous erosion. This was subsequently covered by sediments of the Galilee and Eromanga Basins. Late to Middle Devonian sediments are involved in thrusting that exhibits two styles of deformation. Along the southern 70 km of the thrust front Lower to Middle Devonian sediments are thrust under an upper decollement forming a passive roof duplex or backthrust zone. The Boree Salt acts as this upper decollement. The thrust tipline is controlled by the western depositional edge of the salt. North of this area the thrust appears to have been weakly emergent. Proprietary and open file seismic data from ATP's 301P, 304P and 305P and surrounding permits are used to illustrate the model. Comparisons can be made between this model and similar thrust systems in the Canadian Rocky and Mackenzie Mountains, the Appalachian Plateau, the Southern Norwegian Caledonides, the Kirthar and Sulaiman Mountain ranges of Pakistan and the Papua New Guinea fold belt.