A comparison of evaporite facies in the late Paleozoic Amazon and the Middle Cretaceous South Atlantic salt basins

Large evaporite basins are characterized by a cyclic alteration of sediments deposited under an arid climate in marine, lagoonal, and subaerial environments, respectively. In the Permo-Carboniferous Amazon Basin, marine calcarenites are abundant, lagoonal sediments consist mostly of coarse halite, and nodular anhydrite was formed below the dry salt flats. In this basin, dominantly marine conditions passed into lagoonal, and ultimately the lagoon broke up into disconnected salt lakes. In contrast, at least in the Sergipe embayment of the Cretaceous South Atlantic salt basin, marine sediments are absent, coarse halite is restricted to "tidal"-type feeding channels, and the marginal lagoons, lakes, and salt flats are characterized by a wide array of carnallite tachyhydrite facies. These differences reflect the greater isolation of the South Atlantic graben from the world ocean.