Abstract

In South Australia, canyons 200–250 km long are incised to depths of c. 1.5 km in late Neoproterozoic (after c. 590 Ma) marine deposits of the Adelaide fold belt and canyons 90 km long and 700 m deep occur in correlative marine strata of the Officer Basin 1000 km to the NW. In the Adelaide fold belt, the isotopic signature of limestone veneering canyon walls, canyon sinuosity and sedimentary structures in canyon fill suggest that the canyons were cut subaerially and filled by shallow-water marine deposits during coastal onlap. Eustacy cannot account for the kilometre-scale change in sea level required for subaerial canyon erosion and chemostratigraphy and the lack of evaporites at that stratigraphic level in southern Australia argue against a Messinian-style drawdown. In each region, uplift and crustal extension preceding or coeval with canyon incision are indicated by a regional unconformity, turbidite or mass-flow deposition, and extensional faults. These features and canyon incision may be explained by regional uplift above a rising mantle plume over a distance of >1000 km in southern Australia. Flood basalt volcanism in the Officer Basin tentatively dated at 563±40 Ma may have followed this uplift. Mantle plume uplift is expressed in the sedimentary record by emergent trends in facies, regional thinning, regional unconformities, turbidites, gravity slides, normal faults and incised canyons and palaeovalleys.

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