Exhumed lateral margins and increasing flow confinement of a submarine landslide complex

Abstract

Submarine landslides, including the basal shear surfaces along which they fail, and their subsequent infill, are commonly observed in modern seabed and seismic reflection data sets; their resultant relief impacts sediment routing and storage patterns on continental margins. Here, three stacked submarine landslides are documented from the Permian Ecca Group, Laingsburg depocentre, Karoo Basin, South Africa, including two superimposed lateral margins. The stratigraphic framework includes measured sections and correlated surfaces along a 3 km long, 150 m high outcrop. Two stacked 2·0 to 4·5 km wide and 90 m and 60 m deep erosion surfaces are recognized, with lateral gradients of 8° and 4°, respectively. The aim of this study was to understand the evolution of a submarine landslide complex, including: evolution of basal shear surfaces/zones; variation of infill confinement; and location of the submarine landslides in the context of basin‐scale sedimentation and degradation rates. Three stages of formation are identified: (i) failure of submarine landslide 1, with deposition of unconfined remobilized deposits; (ii) failure of submarine landslide 2, forming basal shear surface/zone 1, with infill of remobilized deposits and weakly confined turbidites; and (iii) failure of submarine landslide 3, forming basal shear surface/zone 2, with infill of remobilized deposits and confined turbidites, transitioning stratigraphically to unconfined deposits. The expression of basal shear varies laterally, from metres thick zones in silt‐rich strata to sharp stepped surfaces in sand‐rich strata. Faulting and rotation of overlying bedding suggest that the shear surfaces/zones were dynamic. Stacking of landslides resulted from multi‐phase slope failure, increasing down‐dip topography and confinement of infilling deposits. The failure slope was probably a low supply tilted basin margin evidenced by megaclast entrainment from underlying basin‐floor successions and the lack of channel systems. This study develops a generic model of landslide infill, as a function of sedimentation and degradation rates, which can be applied globally.

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

“…Previous studies have demonstrated that stepped slopes evolve temporally, often attributed to active mobile substrates or tectonics (Prather, 2003;Hay, 2012;Jobe et al, 2017; Fig. 1E), healing of mini-basins (Satterfield and Behrens, 1990;Prather et al, 1998;Prather, 2003), or through healing of initial mass-wasting generated slope relief (Shultz and Hubbard, 2005;Romans et al, 2011;Brooks et al, 2018a). An example of topographic relief being healed through time (Phase 1, Fig.…”

An integrated process‐based model of flutes and tool marks in deep‐water environments: Implications for palaeohydraulics, the Bouma sequence and hybrid event beds

“…B). Secondly, the flow may be broken longitudinally into a series of debritic and turbiditic components, reflecting retrogressive failure up‐dip (Piper et al., ; Brooks et al., 2018b), or the debris flow component may split into a series of discrete blocks during flow transformation (Felix & Peakall, ; Felix et al., ). In this case, the first debritic pulse cuts the grooves, followed by deposition from the subsequent turbidity current and debritic components (Fig.…”

Syndepositional tectonics and mass-transport deposits control channelized, bathymetrically complex deep-water systems (Aínsa depocenter, Spain)

“…MTD-Top Topography.---The effects of MTD-top and -margin topography are similar. MTDs, particularly large slumps and slides, often exhibit very complex topography on their tops (Armitage et al, 2009;Kneller et al, 2016;Brooks et al, 2018;Ward et al, 2018;Bull et al, 2020). Depressions elongate in the direction of paleoflow provide lateral confinement and are likely to encourage channelization (Fig.…”