Nature of the continent-ocean transition on the non-volcanic rifted margin of the central Great Australian Bight

Abstract

A region of 50–120 km width defines the continent-ocean transition (COT) in the central Great Australian Bight. It is characterized by a thin apron of post-break-up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement. Recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the COT and basement ridge. Modelled gravity and magnetic data, and features interpreted from seismic data, are consistent with aspects of extensional and break-up models proposed for the West Iberia margin. Many of the features and relationships observed beneath the outer margin of the central Great Australian Bight can be explained by extension within a lithosphere-scale ‘pure-shear’ environment involving four layers: brittle upper crust and upper mantle, and ductile lower crust and lower lithospheric mantle. The COT is interpreted to be underlain by extended continental lithosphere. Thus, the continent-ocean boundary is unequivocally defined between oceanic crust and the COT and appears to be associated with sea-floor spreading magnetic anomaly 33, indicating that break-up and sea-floor spreading did not commence until c. 83 Ma (early Campanian time), later than the currently accepted 95 Ma age. The major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting. The magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly, but one that does not relate to break-up and sea-floor spreading.

Cenozoic environmental changes along the East Antarctic continental margin inferred from regional seismic stratigraphy

“…We interpret the oldest regional horizons CS1 and WL1 as correlating with asynchronous continental breakup that occurred in the Early Cretaceous between Greater India and East Antarctica (Region I, about 132.5 Ma; e.g. Powell et al, 1988) and in Late Cretaceous between Australia and East Antarctica (Region II, about 83 Ma; Sayers et al, 2001;Leitchenkov et al, this volume). Horizon "2" is mapped only on the EAM from the Cosmonaut Sea to the Davis Sea (CS2) and is absent in the Mawson Sea.…”

Impacts of Neogene-Recent compressional deformation and uplift on hydrocarbon prospectivity of the passive southern Australian margin

“…Likewise, continental break-up propagated eastwards in a diachronous manner, with seafloor spreading initiated south of the Bight Basin during the late Albian-early Campanian (~95-83 Ma) (Tikku and Cande, 1999;Sayers et al, 2001). The exact age of the first oceanic crust formed off the Otway Basin is debated, with some suggesting that slow-spreading commenced during the Maastrichtian (~67 Ma; Krassay et al, 2004) and others claiming that breakup occurred during the mid Eocene (~44 Ma) coeval with the onset of fast-spreading between Australia and Antarctica (Norvick and Smith, 2001).…”

The Evolution of Mid-Latitude Faunas During the Eocene: Late Eocene Lizards of the Medicine Pole Hills Reconsidered

“…Ocean currents are inferred to have flowed west and north of Australia and east of the LCNZ continental block. Early in the Late Cretaceous, rifting caused marine transgression into the AAG from the west, and seafloor spreading commenced between ~95 Ma (Veevers, 1986) and ~83 Ma (Sayers et al, 2001 …”