Sand-drift surfaces are sharp, generally erosional surfaces separating waterlaid deposits from overlying eolian sand-sheet deposits. They form in many modern playa-lake, ephemeral-stream, and alluvial-fan environments, but have rarely been reported from ancient sequences.
Sand-drift surfaces are an important type of bounding surface, one which marks the transition from subaqueous to eolian depositional processes, thereby providing valuable information for environmental reconstructions, architectural element analysis, and short- and long term climate changes. Because of their nature, sand-drift surfaces cannot be described by existing bounding-surface classifications. To overcome some of the classification problems, we suggest a simple nonhierarchical terminology.