Slope channels on an active margin: a 3D study of the variability, occurrence, and proportions of slope channel geomorphology in the Taranaki Basin, New Zealand

Abstract

The study of active margin channels has become more accessible with the increased amount of high resolution three dimensional seismic surveys. Channels play an important role in sediment transport from continental region to the sea floor basin. Slope channels are also important reservoirs for petroleum. The Kokako three dimensional seismic survey located west of the Taranaki Peninsula of North Island New Zealand in the Taranaki Basin was used to study Tertiary slope channel development. Eight horizons were mapped and surfaces generated to study the timing of development and morphology of channel systems. Dimensions of channel depth, channel width, and channel length were recorded, and channel sinuosity and width to depth ratios were calculated. Channels found in this region occurred as both individual channels, channel complexes, and as confined channels within a canyon. Stacking patterns observed included components of vertical aggradation as well as lateral migration. Channels on the surfaces had both straight and sinuous morphology. Channel depth ranged from 11 to 393 m, channel width ranged from 65 to 4,462 m, and centerline length of the measured channel ranged from 537 to 47,426 m. Channel sinuosity in the study area ranged from 1.00 to 1.39, and the width to depth ratio ranged from 3 to 63. A number of channel dimensions observed in this study increase in width and decrease in thickness as they move upwards in the stratigraphic column. This trend of increasing width and decreasing thickness during channel evolution indicates that the channels developed such that the base morphology changed to no longer provide accommodation for channel fill, causing a loss of sediment confinement and increase in width. The observed trend in channel aspect ratio and lack of levees indicate that flows responsible for these channels were sheet-like turbidity currents.