FINE SEDIMENT DEPOSITIONAL CONTROLS ON THE INNER-SHELF: WAIAPU RIVER, NEW ZEALAND

The highly energetic, gently sloping inner shelf of the Waiapu River, North Island, New Zealand is composed of a minimum of 47% fine sediments. Seismic profiles ground-truthed by cores indicate substantial spatial variation in the shallow, preserved stratigraphy of the inner-shelf. Hypopycnal deposition appears to dominate north of the river's mouth and within a region of semi-enclosed, rocky basins. In contrast, hyperpycnal deposition is evident in comparable water depths just south of the river's mouth. Spatial and temporal variability in modes of deposition may result, in large part, from the effect of antecedent geology in steering bathymetric flows and dictating shelf slope, as well as oceanographic processes that may vary temporally as a function of river discharge. In order to assess the importance of key depositional controls, the carrying capacity for quiescent and storm-driven velocities was calculated for each region in order to determine their deposition potential. Differences in initial deposition and preservation potential have implications for spatial variability in strata formation on active margins.