Characterisation of aeolian sediment accumulation and preservation across complex topography

Abstract

Topography fundamentally influences the distribution and morphology of aeolian landforms via the modification of surface wind flow and the creation of space for sediment deposition. This has been observed at both landform (individual topographic dune forms) and macro-landscape (sand sea) scales. Although previous studies have considered several aspects of the impact of topography on aeolian landforms, the patterns of landscape-scale aeolian sediment accumulation that emerge at the meso-scale, within topographically complex environments have received less consideration. To address this, we present an approach that combines information on the presence of surficial sand (via remote sensing) with the morphometric feature classification method, LandSerf. Using the Cady Mountains in the Mojave Desert as a case study, we explore the relationships between sand cover and topographic indices over length scales of 102–103 m. Field observations are then used to refine our understanding of these patterns. Aeolian deposits across the Cady Mountains are strongly controlled by the topography. Although sand cover is often continuous and highly variable in depth, four archetypal “accommodation space types” are identified from the morphometric analysis: Slopes, Plains, Valley-Fills, and Slope-Valley composite. Specific aeolian landforms within these accommodation spaces may manifest as sand ramps and climbing - falling dunes, particularly on mountain front Slopes, and as sand sheets on downwind Plains within the mountain block. In areas of high sediment supply these may also coalescence, as exemplified by the extensive and compositionally complex Slope-Valley composites in the northern Cady Mountains. In conjunction with field observations, we argue that topography, moderated by proximity to sediment supply, strongly influences the character of the aeolian sedimentary record. However, even within the relatively complex landscape studied here, 90% of the mapped sand accumulation is associated with the four identified accommodation space types. The implication is that areas of such complex topography are amenable to analysis within the scheme outlined and that this can potentially be used to support interpretations of accompanying dune chronologies.