Potassic salts in Phanerozoic evaporite basins and specific features of salt deposition at the final stage of halogenesis

The study of the final stage of halogenesis is one of the most topical problems of evaporite sedimentation and formation of fossil salt deposits. The spatiotemporal distribution of various sulfate, sulfate-chloride, and chloride mineral assemblages of the final stage of Phanerozoic halogenic basins and the compositional trends of marine sulfate and chloride solutions indicate that crystallization of minerals followed a stable trend, while the metastable (“solar”) trend was typical only when the composition of ancient marine solutions fitted that of the condensed oceanic water. The formation of potassic and potassic-magnesian deposits of the sulfate and chloride types is related to the final stage of halogenesis, whereas magnesian and calcium chlorides are deposited at the eutonic stage. The difference between mineral assemblages of potassic and potassic-magnesian deposits in the Phanerozoic section was controlled by the evolution of marine solutions and the heterogeneity of hydrochemical environment in each halogenic basin.