Block generation, deformation, and interaction of mass-transport deposits with the seafloor: An outcrop‐based study of the carboniferous Paganzo Basin (Cerro Bola, NW Argentina)

Mass‐transport processes are notorious for their ability to carry large blocks or megaclasts, to deform sediments, and to interact with the seafloor through deformation and/or erosion of the substrate. These processes, together with their influence on slope sedimentation, are themes we address via direct field observation of three Carboniferous‐aged mass‐transport deposits (MTDs) (labeled I, II, and III) from Cerro Bola, NW Argentina. Internal deformation can be observed in all three MTDs, although it is best developed in MTD II, a 180 m thick vertically zoned MTD with deformation evolving upward from a simple shear dominated base to a pure shear middle zone and finally back into a simple shear dominated topmost zone. The contact between MTDs I and II and their underlying sandstone substrates are also locally deformed, with plastic deformation affecting up to ~20 m of substrate below the MTD base. Conversely, the basal contact between MTD II and the substrate is also in part erosional, marked by scours and grooves that truncate the bedding in the topmost layers of the substrate. Additionally, the presence of large blocks composed of diverse lithologies embedded within the MTDs, together with the sedimentological description of the MTD’s matrix and the aforementioned interaction with the seafloor, suggests at least two processes accountable for block generation within MTDs.