Evolution of the Holocene Coastal Barrier of Pelotas Basin (Southern Brazil) - a new approach with GPR data

Results from a subsurface study performed in the coastal barrier of the Holocene portion of Pelotas Basin along coastal sectors showing progradational, aggradational and retrogradational behavior during the Middle and Late Holocene are presented. The Ground Penetrating Radar (GPR) was used to evaluate subsurface records of the barrier with the aim of defining barrier behavior during a small sea level fall. In sectors of coastal plain where strandplains (regressive barriers) were identified, GPR subsurface records are characterized by oblique reflectors dipping basinward. In sectors where the barrier dunefields are transgressing backbarrier terrains the stacking pattern is retrogradational, which is evidenced by oblique reflectors dipping toward the continent. Between the progradational and retrogradational sectors, GPR records are characterized by basal oblique reflectors dipping landward, while the top reflectors are parallel and subparallel. This distinct basal and top pattern corresponds, respectively, to transgressive and stationary (aggradational) phases of barrier evolution. These results indicate that the shoreline of the emerged portion of Pelotas Basin has experienced transgressive, regressive and aggradational behavior along 1,000 km of coastline during the Middle and Late Holocene.