Eastern New Zealand Drifts, Miocene-Recent

Abstract

Abstract Sediment from New Zealand passes into the north-flowing SW Pacific deep western boundary current (DWBC) to form widespread drifts. South of 49¼S, where the DWBC is reinforced by the Antarctic Circumpolar Current, drifts are small and, in the case of Campbell 'skin' Drift, reduced to a veneer over oceanic sediments. North of 49¼S deposition prevails with (1) Chatham Terrace Drifts - 350 km long and 320 m thick deposits around eastern Chatham Rise at 3000 m depth, (2) Chatham Deep Drift - 400 m thick, 300 km long ridge around the 4500-5000 m deep rise base, (3) Louisville Moat Drift -400 m of sediment within an isostatic depression along Louisville Seamount Chain and (4) Rekohu Drift - a 250 km long, 480 m thick ridge of Oligocene to Recent sediment. These drifts are sparsely surveyed, but two others have sufficient detail to be case studies. North Chatham Drift plasters northern Chatham Rise at 2000-4500 m depth. Drilling recovered 587 m of nannofossil ooze/chalk with cyclical amounts of terrigenous detritus and reworked subantarctic microfossils. Deposition has been almost continuous since the early Miocene. Hikurangi Fan-drift is a 300 km-long lobe, developed down-current of Hikurangi Channel/Fan through redirection of turbidity current plumes by the DWBC at 4850->5500 m depth. Seismically, the drift core comprises 200-360 m of probable Miocene palaeo-drift formed prior to the Pleistocene inception of Hikurangi Channel when 400 m of fan-drift accumulated.