Discussion on Mantle Plume Uplift in the Sedimentary Record: Origin of Kilometre-Deep Canyons within Late Neoproterozoic Successions, South Australia

Nicholas Christie-Blick writes: Kilometre-deep buried canyons in the upper Neoproterozoic successions of South Australia are unusual by any standard, and any viable explanation for their origin will probably involve an unusual set of circumstances. Williams and Gostin (2000) review published geological constraints and competing hypotheses, and suggest a role for uplift and crustal deformation associated with the passage of a mantle plume. On the basis of available evidence, I continue to favour an alternative explanation—that they are due to the short-lived evaporative drawdown of sea level in a marine embayment that became temporarily isolated from the global ocean. Response: Canyons more than 1 km deep in the Wonoka Formation of the Adelaide fold belt and up to 700 m deep in the subsurface of the eastern Officer basin are reasonably interpreted as coeval and of common origin, with a length scale of order 1000 km. Comparable erosional features are found nowhere else in Australia, even in the Kimberley region and western Officer basin, where flood basalts of possible plume origin are widespread. Bender (2000) independently noted the distribution of late Neoproterozoic to early Palaeozoic magmatism in Western Australia, and analyzed the possible role of plume-related uplift and erosional thinning of the crust in early Palaeozoic subsidence of the Canning basin. However, that basin is some 2000 km to the northwest of the Adelaide fold belt, where the canyons are best known