Substrate Entrainment, Depositional Relief, and Sediment Capture: Impact of a Submarine Landslide on Flow Process and Sediment Supply

Abstract

Submarine landslides can generate complicated patterns of seafloor relief that influence subsequent flow behaviour and sediment dispersal patterns. While the large-scale morphology of submarine landslide deposits, or mass transport deposits (MTDs), can be resolved in seismic data, the nature of their upper surface, and its impact on facies distributions and stratal architecture of overlying deposits, is rarely resolvable. MTD is a commonly used term in subsurface studies, covering a range of processes and resultant deposits that can not be resolved in seismic or core-based datasets. However, field-based studies often allow a more detailed characterisation of the deposit. The early post-rift Middle Jurassic deep-water succession of the Los Molles Formation is exceptionally well-exposed along a dip-orientated WSW-ENE outcrop belt in the Chacay Melehue depocentre, Neuquén Basin, Argentina. We correlate 27 sedimentary logs constrained by marker beds to document the sedimentology and architecture of a >47 m thick and at least 9.6 km long mud-rich debrite. The debrite overlies ramps and steps, indicating erosion and substrate entrainment. Megaclasts sourced from shallow-marine environments support a shallow marine origin of the mass failure. Two distinct sandstone-dominated units overlie the debrite. The lower sandstone unit is characterised by: i) abrupt thickness changes, wedging and progressive rotation of laminae in sandstone beds associated with growth strata; and ii) detached sandstone load balls within the underlying debrite. The combination of these features suggests syn-sedimentary foundering processes due to density instabilities at the top of the fluid-saturated mud-rich debrite. The debrite relief controlled the spatial distribution of foundered sandstones. The upper sandstone unit is characterised by thin-bedded deposits, locally overlain by medium- to thick-bedded lobe axis/off-axis deposits. The thin-beds show local thinning and onlapping onto the debrite, where it develops its highest relief. Facies distributions and stacking patterns record the progradation of submarine lobes and their complex interaction with long-lived debrite-related topography. These characteristics can help us understand post-depositional processes above MTDs and predict facies distributions and palaeoenvironments in subsurface datasets. The emplacement of a kilometre-scale debrite in an otherwise mud-rich basinal setting and accumulation of overlying sand-rich deposits suggests a genetic link between the mass-wasting event and transient coarse clastic sediment supply to an otherwise sand-starved part of the basin.

Channel incision into a submarine landslide on a Carboniferous basin margin, San Juan, Argentina: Evidence for the role of knickpoints

“…This raises the question as to what process(es) would lead to such a rapid and repeated decrease in local base‐level? Given that these channels are cut into a >200 m thick MTD, then there is probably substantial relief, and commensurate high gradients, on the basin‐facing slope of the landslide (Martínez‐Doñate et al, 2021; Steventon et al, 2019). Flows traversing such steep slopes are known to be associated with upstream migrating knickpoints (Tek et al, 2021), and knickpoint heights can be >10 m in submarine channels (Gales et al, 2019; Guiastrennec‐Faugas et al, 2020, 2021; Heijnen et al, 2020).…”

“…Submarine landslides, or mass‐transport complexes (MTCs), and submarine channel systems are common features in deep‐water environments. The interactions of submarine channels and landslides play a key role in the behaviour of sediment gravity flows, and govern sediment dispersal patterns (Martínez‐Doñate et al, 2021; Nardin et al, 1979; Piper & Normark, 1983; Pirmez & Flood, 1995; Tek et al, 2020). Changes in sediment supply and routing patterns as a result of the emplacement of a submarine landslide, the relief of the landslide deposit and the behaviour of sediment gravity flows are inherently complex (Alves, 2015; Martínez‐Doñate et al, 2021).…”

Submarine Crevasse Lobes Controlled by Lateral Slope Failure in Tectonically-Active Settings: An Exhumed Example From the Eocene Aínsa Depocentre (Spain)

“…Sediment gravity flows travelling over debrites can show complex patterns of flow behaviour and resultant deposit character due to the upper surface rugosity of the debrite, which promotes rapid deposition (and associated foundering) and/or erosion and channelisation (Armitage et al, 2009;Fairweather, 2014;Kneller et al, 2016;Valdez et al, 2019;Tek et al, 2020;Martínez-Doñate et al, 2021;Allen et al, 2022).…”

The influence of creeping slope failure on turbidity current behaviour

“…Prather, 2000, 2003; Helland‐Hansen & Hampson, 2009; Ryan et al ., 2009; Prather et al ., 2017; Nyberg et al ., 2018) and gravity‐driven slope failures (e.g. Armitage et al ., 2009; Kneller et al ., 2016; Ward et al ., 2018; Bull et al ., 2020; Tek et al ., 2020; Martínez‐Doñate et al ., 2021). The latter generate erosional scars, and deposit slumps, slides and debrites, collectively termed mass‐transport deposits (MTDs) (Bull et al ., 2009; Sammartini et al ., 2019; Shanmugam, 2019).…”

“…Butler & McCaffrey, 2010; Butler & Paton, 2010; Dalton et al ., 2017; Braathen et al ., 2018; Carey et al ., 2019), but considerably less on the kinematic/dynamic nature of the top surface (e.g. Armitage et al ., 2009; Martínez‐Doñate et al ., 2021). Kinematically, their resulting MTDs can be subdivided into: (i) an upslope extensional headwall domain characterized by a normal sense of movement on the basal shear surface, with or without associated synthetic and antithetic normal faults in the hangingwall; (ii) an intermediate translational domain characterized by (a zone of) bedding‐parallel shear at the basal slide surface, transcurrent shear at the lateral margins, and mixed extensional and contractional deformation of the overriding material; and (iii) a downslope contractional toe domain characterized by thrusting at the basal shear surface, with or without the formation of downslope verging folds and thrust‐duplex structures in the hangingwall (Lewis, 1971; Bull et al ., 2009).…”