EARTH zyxwvutsrqp SURFACE PROCESSES AND LANDFORMS, VOL. 20, 105-1 13 (1995) SALT RAMPS: WIND-INDUCED DEPOSITIONAL FEATURES ON TUNISIAN PLAYAS ANDREW C. MILLINGTON zyxwvu Department of Geography, University zyxwvuts of Leicester, University Road, Leicestrr LEI 7RH, U. K. NICHOLAS A. DRAKE Department of Geography. King’s College London, The Strand, London WC2R 2LS, U.K. KEVIN WHITE Department of Geography, University zyxwvutsrq of Reading, Whiteknights. PO Box 227, Reading RG6 ZAB, zyxw U.K. ROBERT G. BRYANT Department of Earth and Environmental Sciences, University of Stirling, Stirling FK9 4LA. U.K. Received 19 March 1991 Revised 9 December 1993 ABSTRACT Semicircular and crescent-shaped accumulations of salt crystals developed on salt crusts were measured on three Tunisian playas in September 1990. These features have been termed salt ramps. Their morphology and chemistry suggest that they are formed in the late stages of shallow ephemeral lake desiccation in playa basins. They form by salt precipitation from shallow brine lakes that are blown across salt-encrusted playa surfaces by the wind. Moreover, they appear to be short- lived features and their degradation is related to the flooding of playas with less saline water, and possibly rainfall and deflation. KEY WORDS: playas; salt crusts; halite; brine; salt ramps; Tunisia INTRODUCTION Salt crusts in playas develop microtopographic features as a result of salt efflorescence, desiccation and solution (Neal, 1965; Teller et al., 1982; Last, 1984), only remaining smooth when covered by water or when above the capillary fringe (Eugster and Kelts, 1983). Lowenstein and Hardie (1985) describe the different sedimentary and surface features of a typical flooding and desiccation cycle in a playa. As surface water evaporates it becomes increasingly saline, and eventually begins to precipitate salts. Precipitation may occur in the brine and/or at the water-sediment interface. Halite crystals, which precipitate at the lake surface, develop into characteristic cup shapes known as hopper crystals (Teller et ui., 1982). These may sink to the lake floor when large enough and become nuclei for further crystal growth (Lowenstein and Hardie, 1985). Alternatively, they may coalesce to form large rafts of salt floating at the surface of a brine lake. During desiccation, polygons form in the surface crust and diagenetic salt growth occurs within sediments. Cycles of flooding and desiccation lead to the formation of statigraphic sediment-salt couplets. Obser- vations made by ourselves and other researchers (e.g. Teller et al., 1982; Last 1984) suggest that shallow brine pools found on salt crusts in the late stages of desiccation often move under the influence of wind (Teller et al.,. 1982; Torgerson, 1984). Features formed in, and on, the salt crust at this time are probably very short-lived. This, combined with the difficulties of access while the basins are still partly inundated, means that few observations have been made of salt crust features which develop during desiccation. zy 0 1995 by John Wiley zyxwvutsrqp & Sons, Ltd. CCC 0197-9337/95/020105-09