Abstract

“Sediment bypass is a key process in turbidity current dynamics for its role in the distribution of sediment in deep-marine systems. Nevertheless, predicting when turbidity currents are bypassing or depositional (i.e., leaving no depositional record versus leaving a deposit) remains challenging. Using 100 m resolution bathymetric data and high-resolution 3D seismic data of the East Coast Basin, New Zealand, we extracted morphometrics from two submarine slope channels and applied a modelling approach that 1) estimates turbidity current velocity and bulk sediment concentration through the flow superelevation method, and 2) calculate thresholds for net erosional, equilibrium, or net depositional flow through a flow-power flux-balance type sediment transport model. We demonstrate that the flow height, slope gradient and grain-size distribution in the flow determines the down-dip patterns of potential turbidite deposits. Thicker flows and those carrying well-sorted suspensions, can bypass sediment over lower slopes than thinner flows and those carrying more poorly-sorted suspensions. Furthermore, 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. Knowledge of the conditions under which turbidity currents bypass sediment can increase our understanding of the sedimentary processes in deep-marine systems and constrain interpretations of turbidite deposits on modern and ancient systems.”