The development of a burkeite-dominated salt crust – an example of evaporite sedimentation in a saline pan with non-monomineralic deposits



A salt crust from an ephemeral saline lake in northern Namibia includes a basal thenardite layer (Na2SO4), followed by intervals consisting of burkeite (Na6(CO3)(SO4)2) with a palisade-type fabric that are separated by layers of fine-grained burkeite. All palisade burkeite formed as coatings along the sides of the neighbouring intervals and around thin lenses of fine-grained burkeite. During the development of these coatings, the original constituents of the intervals that they now occupy were dissolved. Textural features indicate that the dissolved deposits were composed at least in part of halite crystals. The study of this crust illustrates the complexity of evaporite sedimentation in ephemeral saline lakes where more than one dominant mineral is formed. In the studied basin, selective dissolution of the most soluble salts occurred during flooding stages, partly affecting subsurface occurrences that consisted of continuous beds. The final product is a nearly monomineralic deposit, derived from a layered non-monomineralic formation. The deposit developed to a large extent by subsurface crystal growth in a subaqueous setting, rather than by mineral formation along the brine–sediment interface or under subaerial conditions.