Publication Name: Second South-Eastern Australia Oil Exploration Symposium - Technical Papers
Authors: H.M.J. Stagg, J.J. Veevers, S.L. Eittreim and J.R. Childs
Date Published: December 1986
Number of Pages: 16
Reference Type: Book Section
Abstract:
Multichannel seismic and other geophysical data from the Wilkes Land continental margin reveal that continental crust thins oceanwards by extension in fault-blocks of the lowermost strata. Near the mid Cretaceous continent-ocean boundary, the continental crust, measured from the top of the fault-blocks to Moho, thins to as little as 3 km, and is overlain by high-amplitude reflectors interpreted as flood basalts. The Moho deepens from about 12 km under oceanic crust, to 17 km under the continental rise, and 20+ km under the upper slope.Four major seismic sequences, with a maximum total thickness of about 7 km, are recognised. The uppermost sequence, A, is a highly stratified series of channel levee and contourite deposits deeply cut by canyons above 3500 m water depth. Below a highly reflective unconformity, sequence B is poorly stratified and probably represents a shallow-water shelf deposit. Sequence B downlaps onto surface K1 that marks the uppermost limit of faulting and which in turn downlaps onto the hummocky edge of the oldest oceanic crust. Below K1, sequence C displays a highly variable reflector pattern, with numerous faults of short throw and variable bedding angles. The base of sequence C is an erosional surface (K2) along the tops of fault blocks of the lowermost sequence (D), which is a distinctive set of layered blocks separated by low-angle normal faults.
Two interpretations are offered: (1) K1 is the breakup unconformity, and K2 the rift-onset unconformity, in which case sequence D is probably older than Cretaceous (?Beacon Supergroup), or (2) K2 is the breakup unconformity, the base of sequence D is the rift-onset unconformity, and hence sequence D is of Early Cretaceous age (consistent with the southern margin of Australia).