MODERN SEDIMENTATION AND THE MORPHOLOGY OF THE OUTER SHELF AND SLOPE, WAIPAOA RIVER MARGIN, NEW ZEALAND

Detailed sedimentary analysis is often used to study processes and conditions of sediment transport within submarine dispersal systems. Previous studies of continental margins have shown that the combination of high sediment supply and narrow shelf widths can lead to high rates of sediment accumulation on slopes and create strata which relate to the mode of sediment dispersal. The continental slope off the Waipaoa River, New Zealand, provides a dynamic environment to investigate and compare sedimentation along such a margin. Using a high-resolution dataset of radionuclide, sedimentary, and bathymetric/morphologic interpretations, the nature of sediment dispersal on the outer shelf and upper slope is addressed. Lachlan Canyon in the southern portion, when compared to the upper open slope, shows sediment accumulation rates an order of magnitude higher. Pb-210 profiles and grain-size trends within the canyon show more event-driven profiles than open-slope sites. This accumulation in turn has developed a distinctly different morphology in Lachlan Canyon than other surrounding canyons. Increased sedimentation in the head has muted the extensive shelf-break gullying seen in other canyons. The sediment drape over the infilling canyon head is depicted in seismic profiles as well as bathymetric interpretations by relief and surrounding topology. These investigations reveal contrasting styles of sedimentation at canyon and open-slope sites, as observed elsewhere and also reflect a link between slope morphology and sedimentary processes.