Paleontology of Early Cretaceous deep-water samples dredged from the Wallaby Plateau: New perspectives of Gondwana break-up along the Western Australian margin

Sedimentary and paleontological samples from steep, deep-water escarpments of the Wallaby Plateau, 400 km west of Carnarvon, Western Australia, represent the first collected soft-rock geological data from this immense bathymetric high. The study of this vast marginal plateau of 100 000 km² has been hampered by a paucity of rock data arising from difficulties in sampling in water depths of 2200-5700 m. Only modern carbonate, altered tholeiitic basalts and volcaniclastic rocks have been recorded previously. Variably fossiliferous to unfossiliferous claystone, siltstone and sandstone samples from 12 southern Wallaby Plateau stations (3015-5159 m water depths) range from interpreted paralic to shallow-water marine settings, and contain low to moderately diverse assemblages of Bivalvia, Gastropoda, Ostracoda, Foraminifera, palynomorphs, very rare nannofossils, and teleost fish fragments, which collectively point to an age range of latest Berriasian to Barremian-Aptian in the Early Cretaceous. This age range pre-dates, straddles and post-dates the breakup and opening of the Cuvier Abyssal Plain. Seismic imaging of the Wallaby Plateau exhibits a substantial thickness of both dipping and flat-lying, sub-parallel reflectors beneath parts of the Lower Cretaceous Gondwanan breakup unconformity. This information, taken together with the recent identification of Oxfordian-Kimmeridgian Foraminifera from the same location, indicates the presence of a pre-breakup sedimentary section beneath parts of the Wallaby Plateau.