544 SEDIMENTARY ENVIRONMENTS/Deserts Figure Generation of bounding surfaces in aeolian strata as a consequence of bedform migration (A) Interdune migration surfaces (B) Reactivation surfaces (C) Superimposition surfaces arising from the migration of small bedforms over more slowly migrating parent bedforms Reactivation surfaces may be nested within sets bounded by superimposition surfaces migration of scour troughs on the lee slope of a bedform (Figure 4) Although superimposed dunes and scour troughs can theoretically migrate directly up or down the lee slope of a parent bedform, oblique migration is more common because of secondary airflow along the lee slope of the parent bedform Where both reactivation and superimposition surfaces are developed, the latter always truncate the former ‘Interdune migration surfaces’ result from the migration of bedforms separated by interdunes (Figure 4) The surfaces are carved by the passage of an erosive scour that defines the interdune trough between successive bedforms The depth to which the interdune trough scours as it migrates influences the extent to which deposits of the preceding bedform are eroded Interdune surfaces, which truncate both superimposition and reactivation surfaces, typically extend continuously downwind for distances of hundreds of metres to several kilometres Types of Desert Aeolian System In ‘dry aeolian systems’, the water table lies substantially below the accumulation surface, such that moisture plays no role in influencing sedimentation, and deposition occurs as a result of aerodynamic configuration alone Bedforms in dry systems only commence climbing (i.e accumulating) once they have grown to the point at which interdune flats have been reduced to isolated interdune depressions In ‘wet aeolian systems’, the water table or its capillary fringe is in contact with the accumulation surface, such that moisture influences sedimentation, and deposition occurs as a result of both aerodynamic configuration and moisture content determined by the level of the water table The angle of climb in wet aeolian systems is determined by the ratio between the rate of water table rise and the rate of downwind bedform migration, and such accumulations tend to be characterized by downwind climbing dune strata separated by climbing damp interdune units In ‘stabilizing aeolian systems’, factors such as vegetation and surface cementation influence sedimentation, and deposition occurs as a result of both aerodynamic configuration and the degree and type of surface stabilization For example, vegetation acts to disrupt the primary airflow, leading to a reduction in sand transport capacity and thereby a promotion of accumulation