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The Eromanga region of eastern Australia has undergone at least four major tectonic cycles, the results of which are recognized in the structures seen on seismic sections. The late Proterozoic-early Phanerozoic cycle ended with the formation of the Thomson foldbelt, which forms basement in the region. The subsequent reactivations of the fault systems within this basement and deeper lithosphere have produced the structural styles now important as exploration targets. Most reactivations are interpreted as resulting from crustal shortening events affecting sedimentary strata deposited in an epicontinental, shallow water environment, with small strike-slip adjustments affecting some structures.
The dominant style of deformation evident from the seismic sections is that seen across high-angle thrust faults in other parts of the world, with the amount of overthrusting being comparatively small. Generally, the maximum throw on faults in the Devonian strata can be measured in thousands of meters, whereas those in the Permian-Triassic and Jurassic-Cretaceous strata are a few hundred meters at most.
The Devonian sequences of the Adavale basin and associated troughs were deformed during two Carboniferous events, the first with crustal shortening in a north-south direction and the second in an east-west direction. Associated small strike-slip movements were accommodated along a number of faults, including the Warrego-Grenfield, Warbreccan, and Canaway faults. Southwest of our study area, in the Permian-Triassic Cooper basin, other workers have interpreted a northwest-southeast crustal shortening event during the Late Permian and another wrench-induced northeast-southwest crustal shortening during the Triassic. During the middle Tertiary, a crustal shortening event regionally affected the Jurassic-Cretaceous Eromanga basin sequence and older sedimentary rocks. This event is seen pro inently in a deformation zone between the Canaway and Cunnavalla faults, with the direction of crustal shortening being northeast-southwest. Small strike-slip movements are interpreted as partially decoupling events from neighboring provinces: the Adavale basin and Cheepie shelf to the east and southeast and the Cooper basin and Warbreccan dome to the southwest and northwest, respectively. In this partial decoupling, the Canaway, Cunnavalla, Warrego, and Warbreccan faults are interpreted as playing an important role.
The basin-modifying tectonic episodes within the lithosphere control structural style. These relatively small-scale events have resulted in structures that provide attractive petroleum prospects.
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