Conditions favourable for the formation of warm-climate aeolian sand sheets

Aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent. Sand sheets are ubiquitous to modern, warm-climate sand seas, generally occurring marginal to dune fields, although they may exist within the interior of a sand sea or independent of a dune field. Sand-sheet deposits are recognized in ancient aeolian sequences, where they may account for significant accumulations of low-angle aeolian stratification. We suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets. A study of six modern sand sheets in North America (located at Great Sand Dunes, Gran Desierto, Dumont, Algodones, Padre Island, and Colorado River delta) indicates that the factors favourable for sand-sheet development are: (1) a high water table, (2) surface cementation or binding, (3) periodic flooding, (4) a significant coarse-grained sediment population, and (5) vegetation. These factors are reflected in the nature of stratification and the accessory features of sand-sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the Triassic Dolores and Pennsylvanian-Permian Rico formations.