3-D geometry and luminescence chronology of Quaternary soft-sediment deformation structures in gravels, northeastern Brazil

This paper reports and describes soft-sediment deformation in gravels and gravelly sediments in Quaternary alluvial deposits of the Potiguar Basin, northeastern Brazil. Deformation structures were measured in terms of geometry, size, and relationship with sedimentary bedding using geological mapping and ground penetrating radar. TL and OSL/IRSL methods following MAR and SAR protocols were used to date sediments and soft-sediment deformation events. Our results indicate that soft-sediment deformation structures are widely distributed in several stratigraphic intervals of alluvial-channel deposits in a low-lying topographic valley. Depending on their geometry and composition, two types of soft-sediment deformation structures occur: pockets and dome-like load structures. These structures resulted from the shaking of sediments with a reverse density gradient system, which caused collapse and realignment of pebbles. These features are similar in morphology and size to modern examples of seismically-induced soft-sediment deformation in coarse sediments. TL and OSL ages indicate that sediment deposition and associated soft-sediment deformation occurred at least six times from ~ 352 ka to ~ 9 ka.