QUEENSLAND PLATEAU AND CORAL SEA BASIN STRATIGRAPHY, STRUCTURE AND TECTONICS

Abstract

Seafloor spreading in the Coral Sea Basin is dated by Deep Sea Drilling Project Site 287 as Early Eocene (51 my bp). This requires normal rifting and breakup of an extended Australian continent including the Queensland. Papuan and Louisiade Plateaus as well as the Cretaceous portions of East Papua. A reconstruction based on continental and plateau margin physiography and Papua-New Guinea geology points to a pole of relative opening at lat. 11.3° S., long. 141.3° E. This results in left-lateral transform motion along the Moresby Trough and Bismarck-Lagaip Fault Zones through breakup, plus the deformation of the Owen Stanley sediment pile, and emplacement of the Papuan Ultramafic Belt.

Following initiation of sea-floor spreading, subsidence commenced at what are now the marginal plateaus bordering the Coral Sea Basin. A widespread unconformity spanning the late Eocene-mid Ollgocene can be recognised on all plateaus as well as in the basin proper. This is attributed to the commencement of a significant equatorial circulation pattern in the deepening basin and over the subsided plateaus. Stabilisation of this equatorial circulation pattern permitted coral reef development on residual basement highs on the marginal plateaus and eventually) on the subsiding Queensland continental shelf and Papuan stable platform areas in the late Oligocene-early Miocene.

On the basis of seismic refraction and gravity evidence, rift valley sequences up to 3 km thick are inferred beneath the Queensland and Townsville Troughs and bordering the Queensland and Papuan Plateaus. Though seismic refraction data are lacking, similar sequences are also inferred beneath parts of the Eastern and Marion Plateaus. Bligh Trough and Louisiade Rise. The age of this pre-breakup rifting is suggested to be mid Cretaceous-Palaeocene although direct evidence is absent.

Gravity modelling over the Queensland Trough, Plateau and Coral Sea Basin supports the interpretation from seismic reflection and refraction data. Continental crustal structure with a deep metamorphic layer is indicated for the Queensland Trough and Plateau with a depth to the Moho of 22-28 km. The continental/ocean crust transition occurs towards the base of the continental slope at a water depth of up to 4.5 km along the Queensland Plateau. Crust beneath the Coral Sea abyssal plain is oceanic with a depth to mantle of 11-13 km.