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

Abstract

Emplacement of submarine landslides, or mass-transport deposits, can radically reshape the physiography of continental margins, and strongly influence subsequent sedimentary processes and dispersal patterns. Typically, progressive healing of the complicated relief generated by the submarine landslide occurs prior to progradation of sedimentary systems. However, subsurface and seabed examples show that submarine channels can incise directly into submarine landslides.Here, the evolution of a unique exhumed example of two adjacent, and partially contemporaneous, submarine channel-fills is documented. The channels show deep incision (>75 m), and steep lateral margins (up to 70°), cut into a >200 m thick submarine landslide. The stepped basal erosion surface, and multiple terrace surfaces, are mantled by clasts (gravels to cobbles) reflecting periods of bedloadderived sedimentation, punctuated by phases of downcutting and sediment bypass. The formation of multiple terrace surfaces in a low aspect ratio confinement is consistent with the episodic migration of knickpoints during entrenchment on the dip slope of the underlying submarine landslide. Overlying sandstone-rich channel-fills mark a change to aggradation. Laterally stacked channel bodies coincide with steps in the original large-scale erosion surface, recording widening of the conduit; this is followed by tabular, highly aggradational fill. The upper fill, above a younger erosional surface, shows an abrupt change to partially confined tabular sandstones with normally graded caps, interpreted as lobe fringe deposits, which formed due to down-dip confinement, followed by prograding lobe deposits. Overlying this, an up-dip avulsion induced lobe switching and back-stepping, and subsequent failure of a sandstone body up-dip led to emplacement of a sandstone-rich submarine landslide within the conduit. Collectively, this outcrop represents episodic knickpoint-generated incision, and later infill, of a slope adjusting to equilibrium. The depositional signature of knickpoints is very

Fill‐and‐Spill, Tilt‐and‐Repeat (FaSTaR) cycles: Stratigraphic evolution above a dynamic submarine stepped slope

“…The presence of multiple mud‐ and sand‐filled channels that connect the steps across the ramps (Figures 5, 8 and 11) suggests multiple non‐synchronous sediment conduits. Gradient variations imposed by slope breaks along channel profiles were probably readjusted via up‐dip migrating knickpoints based on observations from modern and ancient systems (Allen et al, 2022; Deptuck et al, 2012; Guiastrennec‐Faugas et al, 2021; Heijnen et al, 2020; Tek et al, 2021). The age relationship between the late‐stage channels and the step deposits requires a high‐resolution stratigraphic framework, which is discussed in the next section.…”

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

“…On the other hand, the sandstones and coarse-grained dune-like deposits indicate deposition from steady (Kneller and Branney, 1995) and bypassing high magnitude energetic flows, which reworked a previously deposited coarser fraction (Amy et al, 2000;Stevenson et al, 2015;Hansen et al, 2021). Furthermore, the lack of channel-scale erosional features within these packages suggests that FA2 corresponds to terrace deposits formed on a relatively flat to shallow surface in an elevated position relative to the active channel, yet still inside the channel belt (Babonneau et al, 2002(Babonneau et al, , 2004(Babonneau et al, , 2010Hansen et al, 2015Hansen et al, , 2017aHansen et al, , 2017bAllen et al, 2022). The basal matrixsupported conglomerates (Lf7c; Fig.…”

“…5B) are considered local deposits of cohesive debris flows (Talling et al, 2012), which might create a relative topographic high with certain rugosity and form the initial terrace surface. The deformed heterolithic units (Lf7a) are attributed to gravitational failures of the channel walls and/or adjacent confining slopes (Hansen et al, 2015(Hansen et al, , 2017bAllen et al, 2022).…”

“…Despite the outcrop limitations and lack of kinematic indicators within the debrites (Bull et al, 2009), the position and composition of submarine landslide deposits within the palaeogeography of the Banastón sub-unit suggests that they were emplaced transversely (Bayliss and Pickering, 2015) and probably related to tectonic pulses, given the tectonically-active nature of the basin and their abundance. Submarine landslides can disturb the slope equilibrium gradient (Corella et al, 2016;Kremer et al, 2018;Liang et al, 2020;Tek et al, 2020) and induce partial or full blockage of the adjacent conduit (Posamentier and Kolla, 2003;Bernhardt et al, 2012;Corella et al, 2016;Kremer et al, 2018;Tek et al, 2020;Tek et al, 2021;Allen et al, 2022).…”

“…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).…”