A new modelling approach to sediment bypass prediction applied to the East Coast Basin, New Zealand

Abstract

Predicting when turbidity currents are erosional or depositional (i.e., leaving no depositional record versus leaving a deposit) remains challenging. Here we combine observations from submarine channel morphology with a new sediment transport model to derive thresholds for net erosional, equilibrium, or net depositional flow to predict how far turbidity currents can transport different grain size classes down the channel. The approach was applied to the modern Madden and Omakere Channels, which traverse the Hikurangi subduction margin of the North Island of New Zealand. A bathymetric data set was used to establish the downstream change of channel geometry. Taking account of centripetal and Coriolis forces, the flow superelevation method was used to estimate variations in flow velocity and concentration along the channels. These parameters were used as model inputs to estimate the potential distribution of sand in the system assuming the separate cases of well-sorted and poorly-sorted sediment in suspension. The predicted sand distribution maps deposited by poorly-sorted flows in the channels show good agreement with root mean square amplitude mapping of the seafloor. These results confirm that thicker flows, and those carrying well-sorted suspensions, can bypass sediment over lower slopes than thinner flows and those carrying more poorly-sorted suspensions. The net erosion and net deposition thresholds derived from this study may help to guide and constrain predictions of potential sediment bypass zones in seafloor and subsurface systems and hence better constrain the predicted loci of deposition.

Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand

“…Typically, the fill of the outcropping basins consists of regularly bedded, mud-rich turbidites, as well as shallow-marine fringes (Bailleul et al, 2007). Although tortuous paths of sediment transport may be expected on such margins, this is not always the case, as observed here (McArthur and McCaffrey, 2019;Crisostomo Figueroa et al, 2020) and other subduction margins (e.g., Cascadia [Nelson et al, 2000] or the Makran [Bourget et al, 2011]), where transverse channels may bypass significant portions of the slope. Specifically, we examine outcropping Lower Miocene strata of the Greenhollows Formation (Fig.…”

Equilibrium sediment transport by dilute turbidity currents: Comparison of competence‐based and capacity‐based models

“…(2020). Equation is used here to modify this model for application to turbidity currents (see also Crisóstomo‐Figueroa et al ., 2020). The criterion is derived from a one‐dimensional sediment suspension model, Eq.…”

Relating seafloor geomorphology to subsurface architecture: How mass‐transport deposits and knickpoint‐zones build the stratigraphy of the deep‐water Hikurangi Channel

“…Full stack data are displayed such that a downward increase in acoustic impedance is shown as a trough (white reflection). The horizontal resolution of the survey is ca 25 m and the vertical resolution is ca 7 m (values accurate at seafloor; Crisóstomo‐Figueroa et al ., 2020). High‐resolution bathymetry rendered from the 3D seismic data is augmented with 25 m grid bathymetry data, provided by New Zealand Petroleum and Minerals (NZPM).…”