-

Abstract

In the desert of Abarkoh Basin, Central Iran, the influence of playa-lake level fluctuations on recent sedimentation mode of a terminal ephemeral fluvial-fan system and adjacent lacustrine/aeolian sediments of a playa fringe environment has been investigated. The surface geomorphology-sedimentology and its relationship with shallow subsurface sediments along a >25 km transect, has been studied. The Abarkoh Basin is a NW-SE trending depression (>150 km long and ~100 km wide) with a megafan (>940 km2) originated to the west and laterally grades into distal fan and playa fringe (desert) environments. The late Quaternary evolution of the area represents the relative dominance of water versus wind transport and deposition as a function of variations in the discharge of ephemeral fluvial systems and fluctuations in groundwater table/playa-lake level. The combination of climatic change, human impact and to a lesser extent syndepositional tectonics resulted in a drawdown of the groundwater table or/and playa-lake level and associated recent periods of extensive deflation/deposition and its related shifts in dune development. Significant erosion and reworking of the dune fields was associated with their position in depocenters, partly controlled by the termination of the fluvial system in the playa periphery and/or the position of playa-lake level. The latter resulted in development of a sandy saline pan. This study emphasizes the importance of the rapid sedimentary and geomorphic environmental modification in distal parts of the terminal fans-playa fringe environments, areas that are particularly sensitive to desertification.