In 1849 the Italian chemist J. Usiglio performed a set of evaporation experiments with seawater along the French Riviera and established the order in which evaporite minerals precipitate from an aqueous environment. On earth these minerals are mostly gypsum and halite, associated with borates, potassium and magnesium salts. These minerals (not surprisingly) if found in a stratigraphic column are compelling evidence for the former presence of water. Fig.1. The Groeden sandstone was deposited in a landscape consisting of a succession of perennial and periodic rivers, alluvial fans, lakes and coastal plains in a semiarid climate (hot and dry with seasonal excessive rainfalls). Pedogenetic horizons with folded gypsum layers record strong evaporation and water level fluctuations. The upper cross-bedded sandstone records periods when meandering fluvial channels alternated with sand dunes of a desert environment.
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