Sealers Bay submarine fan complex, Oligocene, southern New Zealand



The Oligocene Balleny Group of Chalky Island, southwestern Fiordland, comprises a typical continental margin sequence 900 m in thickness. Thin nearshore traction deposited sediments at the base are overlain by submarine canyon and fan lithofacies that were deposited by the full range of subaqueous mass-transport processes. A steep-walled channel within Balleny Group is interpreted as a fossil proximal fan-channel. The sedimentary fill of the channel is texturally similar to sediments moving by slump-creep in Recent submarine canyons and fan-valleys. The field data presented indicate (1) that a small canyon complex at Sealers Bay was initially cut by subaqueous debris-flows derived from an adjacent cliffed continental coast; (2) that transport within the upper parts of the canyon and fanchannel complex was primarily by inertia-flow and slump-creep; and (3) that these more proximal types of mass-transport gave way gradationally and successively to fluxoturbidity and turbidity currents at locations further down-slope, with consequent deposition of sediment in more distal fan-channel and fan-surface environments as fluxoturbidites and turbidites, with lesser contributions from inertia-flows.