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

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