LATE QUATERNARY SEDIMENT PATHWAYS THROUGH THE DEEP OCEAN, EAST OF NEW ZEALAND

Late Quaternary sediment pathways through the deep ocean, east of New Zealand, were determined using sand-sized mica tracers in conjunction with physical oceanographics, seismic, and stratigraphic data. Results indicate that in glacial times, micaceou sediment derived mainly from low-grade metamorphic rocks of the eastern South Island, was delivered by rivers directly to Bounty Trough. Here turbidity currents transferred the sediment 1000 km eastward to the Bounty Fan on the 4500 m deep Southwest Pacific Basin. A western boundary current (WBC), flowing over the fan, redirected the sediment 1000 km to the north and northwest where it eventually accumulated as a drift deposit near Hikurangi Trough. The drift also received mica that had been transported 700 km along Hikurangi Trough from mainly plutonic sources on the northwestern South Island. Interglacial episodes witnessed a major change in transport paths. River-borne sediment was diverted away from Bounty Trough which became a site of predominantly calcareous pelagic sedimentation. Denied the lateral injection of terrigenous sediment, the WBC nevertheless continued to supply small quantities of mica to the drift through erosion of existing glacial deposits on the Bounty Fan. The paucity of interglacial mica on the drift indicates it is also receiving little terrigenous sediment by way of Hikurangi Trough.