The role of mass‐transport complexes in the initiation and evolution of submarine canyons

Abstract

The offshore area of the Otway Basin (south‐eastern Australia) is dominated by multibranched canyons where mass‐transport complexes are widely distributed. This study integrates high‐resolution multibeam and seismic data to investigate the importance of mass‐transport complexes in dictating the evolution of canyons. The study interprets three regionally distributed mass‐transport complexes that fail retrogressively and affect almost 70% of the study area. Within the mass‐transport complexes, seven canyons that initiated from the continental shelf edge and extended to the lower slope are observed. Although the canyons share common regional tectonics and oceanography, the scales, morphology and distribution are distinctly different. This is linked to the presence of failure‐related scarps that control the initiation and formation of the canyons. The retrogressive failure mechanisms of mass‐transport complexes have created a series of scarps on the continental shelf and slope. In the continental shelf, where terrestrial input is absent, the origin of the canyons is related to local failures and contour current activities, occurring near the pre‐existing larger headwall scarps (ca 120 m high, 3 km long). The occurrence of these local failures has provided the necessary sediment input for subsequent gravity‐driven, downslope sediment flows. In the continental slope, the widespread scarps can capture gravity flows initiated from the continental shelf, developing an area of flow convergence, which greatly widens and deepens the canyons. The gradual diversion and convergence through mass‐transport complex related scarps have facilitated the canyon confluence process, which has fundamentally changed the canyoning process. Thus, this study concludes that the retrogressive failure mechanism of mass‐transport complexes has a direct influence on the initiation, distribution and evolution of the canyons. The scarps associated with mass‐transport complexes have greatly facilitated the delivery of sediments and marine plastics from the shelf edge into the deep oceans, especially in areas where fluvial input is missing.

Large-scale submarine landslide drives long-lasting regime shift in slope sediment deposition

“…From the study of the Mms, we propose a conceptual model for the evolution of a continental margin affected by a large-scale landslide (Fig. 4), where the disruption of submarine slope channel systems over a wide area promotes the development of a major conveyor belt through the formation of topographic lows and confluence zones (see also Wu et al, 2022) that focus the transport of land-derived material and trap sediments carried by bottom currents. During the progressive healing of the landslide topography, which we observe can last for several million years, deposition of sand-prone facies may occur primarily on the upper slope, filling up the accommodation space generated by the landslide (Fig.…”

“…Submarine landslides and related mass-transport deposits (MTDs; sensu Weimer, 1990) modify the physiography of continental margins and impact subsequent sediment transport and deposition. Slope failures may capture turbidite channels (Kneller et al, 2016;Qin et al, 2017) and promote the formation of new submarine canyons through retrogressive erosion or by focusing gravity flows (Martínez-Doñate et al, 2021;Wu et al, 2022). The rugose topography of MTDs, generated either by landslide blocks or due to differential compaction (Alves and Cartwright, 2010;Ward et al, 2018), influences the path of subsequent turbidite channels (Bull et al, 2020) and may control the location of channel avulsion (Ortiz-Karpf et al, 2015).…”

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

“…The presence of the stair-stepped scarps in the eastern part indicates that the landslides are initiated on the lower slope and fail retrogressively upwards (i.e. Sawyer et al, 2009;Wu et al, 2022). In the western part, the scattered scarps on the shelf suggest that slope failures dominate the continental shelf area.…”

“…In the Southern region, the evenly spaced nature and the absence of onshore fluvial systems indicate the canyoning process in the Southern region is fully marine and is related to alongshore current activities (Krassay et al, 2004;Mitchell et al, 2007b;Wu et al, 2022). Previous studies indicate the initiation and development of the canyons are attributed to the strengthening of the Bass Cascade Current (BCC) since the Pliocene (Mitchell et al, 2007a).…”

How do ancient mass-transport complexes influence subsequent failure events? A case study from the Kangaroo Syncline, offshore NW Australia

“…Kneller et al, 2016). Previous studies suggest that relief above MTCs influence sediment transport pathways by diverting subsequent turbidity currents (Hansen et al, 2013;Ortiz-Karpf et al, 2015;Corella et al, 2016;Ward et al, 2018;Wu et al, 2022), or by disrupting the equilibrium condition of subsequent alongshelf transported ocean currents and facilitating their transformation into down-slope transported gravity flows (Wu et al, 2024), or by generating ponded accommodation within which (turbidity current-fed) lobes and contourite channels are deposited (Solheim et al, 2005;Olafiranye et al, 2013;Li et al, 2015;Kneller et al, 2016) (see Appendix-2 for details). However, the way in which pre-existing MTCs control the flow direction, depositional pattern, and stratigraphic architecture of subsequent failures has received less attention.…”