MID-BATHYAL CURRENT SCOURS AND SEDIMENT DRIFTS ADJACENT TO THE HIKURANGI DEEP-SEA TURBIDITE CHANNEL, EASTERN NEW-ZEALAND - EVIDENCE FROM ECHO CHARACTER MAPPING

Late Quaternary sedimentary processes on the northwest Chatham Rise continental slope and southern Hikurangi Trough, eastern New Zealand. have been examined using 3,5 Khz seismic reflection profiles, together with piston cores. High frequency echo character mapping of the region shows that the slope has been dominated by current-controlled sedimentary processes, whereas turbidite processes characterise the adjacent part of the southern Hikurangi Trough. On the slope north of Mernoo Saddle, a 580 m deep bathymetric passage between the eastern South Island continental shelf and the Chatham Rise, a 160 km alongslope by 30 km wide region of current erosion occurs between 700 m and 2300 m water depths. Within this region are several northeast trending channels. 5-20 km wide and up to 105 km long, scoured obliquely down slope. These scours are inferred to have been formed mainly during glacial periods by a northward flowing current of subantarctic water passing through the Mernoo Saddle, then braiding as it cascaded down and across the mid-slope before merging again further east into a contour current on the unstable lower slope of the north Chatham Rise. The lower slope in between and below the scours comprises a complex of coalescing sediment drifts. The adjacent part of the southern Hikurangi Trough is characterised by a canyon/leveed-channel system receiving turbidites from the eastern South Island continental margin and Cook Strait. Mapping reveals a meandering channel up to 10 km wide on the floor of the trough, with a left-bank dominated levee east of Cook Strait. where the trough widens.