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

Abstract

Dense shelf water cascades (DSWC) are ubiquitous on continental margins worldwide. They could transform into turbidity currents, shape the seabed physiography, and influence sediment, organic carbon, and pollutants that transfer from the shelf to the basin floor. However, there is still a lack of knowledge regarding how DSWC transforms into turbidity currents, and how DSWC interacts with the seabed. The Central Region of the offshore Gippsland Basin, located on the southeast Australian margin, is seasonally impacted by DSWC (named the Bass Cascade Current; BCC) formed in the Bass Strait. We observed complex seabed morphologies and highly diverse sedimentary processes in this area using high-resolution multibeam bathymetry, seismic reflection, and core description data. Observed sedimentary structures include sediment waves, erosional scours, cyclic steps, submarine channels, longitudinal furrows, submarine landslides and gullies. We ascribe this complexity to a dynamic interaction between BCC, and Westerly wind-associated Ekman transport flow, and strong waves. We found that the along-shelf transported BCC can interact with the submarine landslides and generate supercritical turbidity currents transporting downslope for more than 80 km. We reveal that climate change could significantly impact the seabed morphologies and sedimentation processes, by dictating the strength and pathway of BCC and its generated supercritical turbidity currents. Therefore, the current transformation has critical implications for predicting how seabed geomorphology, sedimentation process, and occurrence of geohazards respond to changing oceanographic and climate conditions.

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.…”

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

“…The BCC is a high-energy current with an average transport rate of 3.6 km 3 /h (Godfrey et al, 1986). During transportation, the BCC could generate near-bottom gravity flows (dominantly turbidity currents) that transport across the shelf, and downslope over tens and hundreds of kilometres (Ivanov et al, 2004;Wu et al, 2023). In the Central region, the shelf is also dominated by seasonal eastward flowing westerly wind at a speed of 10-30 km/h (especially in winter; Li et al, 2005).…”

“…Interpretation: Wu et al (2023) have thoroughly investigated the initiation and evolution of these seabed morphologies and dominant sedimentary processes in the Central region. It was suggest that the complex seabed morphology in this region is genetically linked to a dynamic interaction between Bass Cascade Current, Westerly wind, and strong waves (Wu et al, 2023). The NNE-trending scarp developed on the shelf is interpreted as the headwall scarp of larger buried submarine landslides (i.e.…”

“…Based on Wu et al (2023) the headwall scarp developed on the shelf could catch the along-shelf transported BCC, forcing it to sink and generate supercritical turbidity currents. The supercritical turbidity currents further transports downslope, forming the widely distributed gullies and other erosional structures on the slope.…”

“…The supercritical turbidity currents further transports downslope, forming the widely distributed gullies and other erosional structures on the slope. The Westerly winds and associated waves could also impact the area off-shelf and across the upper slope, forming submarine landslides and initiating turbidity current (Wu et al, 2023).…”