Abyssal sediment drifts, erosion and history of bottom water flow in the Tasman Sea southwest of New Zealand

Abstract

Deep‐sea sediments in the southeastern Tasman Sea underwent extensive bottom current erosion and transport during the late Cenozoic. Analysis of seismic facies shows that a northward flow caused profound erosion in narrow scoured deeps and over wide areas in the southeastern Tasman Sea southwest of New Zealand. At 47°S the flow diverted north‐northwest into the central Tasman Sea and a large lobate laminated sediment drift was constructed at the turn. The flow directions are established from mega‐bedform geometries in and on the drift and from the asymmetry of sediment remnants in the regions of profound erosion. Current activity and erosion began late in the Eocene or early in the Oligocene, probably due to both oceanographic and geographic changes at that time. Oceanographic data show that flows with similar erosional strength do not operate today. To explain the severity of past erosion by northward flows at this very eastern location in the basin, it is proposed that at times in the late Cenozoic, north‐directed bottom water flows entering the Tasman Sea were forced towards the eastern basin margin by eastward and northward entrainment under the Antarctic Circumpolar Current south of 47°S.