Abstract

Sedimentological and architectural data from three-dimensional larger vertical outcrops of Pleistocene fluvial deposits of the Dandiero Basin (Eritrean Danakil depression) are here used to reconstruct planform evolution of a meander bend and investigate the role of overbank flooding in sediment distribution on point bars. The point bar accumulated as part of a lowstand systems tract at the base of an incised valley cut into lacustrine mud. Selected outcrops transect a 1-km-long channel belt exposed parallel to the main fluvial transport direction. Sedimentological logs, outcrop line drawings, and paleocurrent and bedding measurements show that this outcrop belt represents a transverse section of an asymmetric fluvial point bar, which accumulated through migration of a channel 6 m deep and 70 m wide. This bar was characterized by early expansion followed by downstream accretion, which was abruptly interrupted by lacustrine deposition. The onset of downstream accretion started when the channel expanded to reach the more resistant valley wall. Sediment accreted on the downstream side of the point bar and accumulated both during bankfull discharge and overbank floods, with significant modification of the channel flow where the floodwater re-entered the main channel (i.e., riffle zone). In this zone, a secondary circulation cell triggered a shift of erosion toward the inner bank and scrolling on the downstream side of the point bar.