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

Abstract

Cretaceous sedimentary rocks corresponding to the Las Plumas Member of the Cerro Barcino Formation were deposited in the eastern margin of the Somuncurá - Cañadón 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.