Soft-sediment deformation structures in gravelly fluvial deposits: A record of Cretaceous seismic activity in Patagonia?

Cretaceous sedimentary rocks corresponding to the Las Plumas Member of the Cerro Barcino Formation were deposited in the eastern margin of the Somuncura - Canadon Asfalto Basin. The analyzed succession records alluvial settings in a fault-proximal scenario and contains a 7 m thick stratigraphic interval bearing soft-sediment deformation structures which include: pebble load casts, pseudonodules, flame structures and contorted bedding. Deformed beds are bounded by undisturbed strata and these features can be traced along the 800 m of exposures. The sedimentological features such as size and shape of SSDS, clast fabric of gravels and depositional paleoenvironment added to the proximity to a fault zone support the interpretation of the described deformation features as formed by liquefaction and/or fluidization triggered by seismic shocks during syn-tectonic deposition.