The Structural and Stratigraphic Evolutions of Shale Detachment Systems in the Ceduna Basin, Australia
Mohd Zaid Jaapar1 and Ken McClay2
1Exploration Geosciences, Petronas Carigali, Kuala Lumpur City Centre, Malaysia
2Geology Department, Royal Holloway College, University of London, Egham, United Kingdom
The Ceduna sub basin, part of the Bight basin, covers an area of 95,000 sq. km and is located at the southern margin of the Australian continent. The basin was formed by the Mid-Late Jurassic to Early Cretaceous separation of southern Australia from Antarctica.
Four principal tectono-stratigraphic phases have been identified in the Ceduna Sub-Basin. Mid-Late Jurassic rifting was followed by two phases of post-rift thermal subsidence in the Cretaceous with southern margin breakup occurring in the Late Santonian. Four episodes of thermal subsidence have been identified and these events are related to a massive sediment influx into the passive margin basin. Two major delta complexes have been identified.
Rapid progradation of Turonian -Santonian and Campanian -Maastrictian deltas on the unconsolidated Albian deep marine shale have produced series of syn -depositional listric faults and shale detachment systems. Two episodes of shale detachment system have been recognized - a Mid Albian and a Late Santonian detachment system. The Mid Albian event is more widespread than the late Santonian event which only dominated the outer margin of the delta. The Mid-Albian event produced a series of southward dipping listric fault systems which are associated with syn depositional growth sequences and contractional toe- thrust systems.
Sediment depocentres are controlled by the syn-depositional fault structures with the initial sedimentation infilling the basin center followed by a shift to the outer delta margin after the basin center has been filled, together with reactivation of the fault along the delta margin. Sediment accumulation in the fault hanging-walls caused the propagation of growth faults, hanging wall rotation and the development of roll-over anticlines.
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