The role of mass-transport complexes (MTCs) in the initiation and evolution of submarine canyons

Abstract

The offshore area of the Otway Basin, located within the SE continental margin of Australia, is dominated by a multibranched canyon system where submarine mass-transport complexes (MTCs) are widely distributed. We integrate high-resolution multi-beam bathymetric and seismic reflection data to investigate the importance of regionally distributed MTCs in dictating the evolution of canyon systems. We interpret three regionally distributed MTCs that fail retrogressively and affect almost 70% of the study area. Within the MTCs, we observed seven canyons that initiated from the continental shelf edge and extended to the abyssal plain. Although these canyons share common regional tectonics and oceanography, the scales, morphology, and distribution are distinctly different. This is devoted to the presence of failure-related scarps (i.e. headwall and sidewall scarps) that control the initiation and formation of the canyons. The retrogressive failure mechanisms of MTCs have created a series of the headwall and lateral scarps on the continental shelf and slope regions. In the continental shelf, where terrestrial input (i.e. fluvial systems) is absent, the origin of the canyons is related to the local failure events and the contour current activities occurring near the pre-existing, massive headwall scarps (c. 120 m high, 3km long). The occurrence of these local failures has provided the necessary sediment input for subsequent gravity-driven, downslope sediment flows. In the continental slope region, the widespread scarps can capture gravity flows initiated from the continental shelf, developing an area of flow convergence, which greatly widens and deepens the canyon system. The gradual diversion and convergence through MTCs related scarps have facilitated the canyon confluence process, which has fundamentally changed the canyoning process. Thus, we conclude that the retrogressive failure mechanism of MTCs has a direct contribution to the initiation, distribution, and evolution of the canyons, especially in areas where fluvial input is missing. Moreover, the retrogressive failure mechanism is responsible for the canyon deepening and confluence process, which can greatly facilitate the delivery of sediment into deep oceans.

Complex seabed geomorphology shaped by various oceanographic processes: a case study from the Gippsland Basin, offshore south-eastern Australia

“…We interpret that the most likely erosional process is gravity flows generated by canyon sidewall failures (i.e. Wu et al, 2021). The shift in the canyon transportation direction from SE to SW is primarily controlled by the local topography created by the regional Rosedale Fault (Figure 1C).…”

Transformation of dense shelf water cascade into turbidity currents: insights from high-resolution geophysical datasets

“…Near the upper slope, the step-shaped pattern of the scarps suggests a retrogressive failure mechanism of the landslides (Figure 7B; Wu et al, 2021). As the landslides are located along the shelf edge, where cyclic wave loading can constantly rework seabed sediments.…”