Genetic Model of Mud-Clast Conglomerates in Salt Rocks and Their Significance for Salt Mineralization in Mohei Area,...

The Simao Basin is one of the most important Mesozoic salt basins in China, and the salt rocks generally contain mud-clast conglomerates. The characteristics of mud-clast conglomerates can provide effective information indicating the evolution process of the salt deposits. A combined analysis of trace elements and clay minerals was performed to characterize the genetic model of mud-clast conglomerates in the salt rocks. The results show that the sedimentary materials are felsic rocks from the Upper Crust. Ternary plot diagrams show that the tectonic settings are between the continental margin and the continental island arc. The clay minerals in the samples mainly contain illite and illite-smectite mixed layers. A dry and hot climate prevailed during the deposition of the Mengyejing Formation, and the warm-humid climate that also occurred is interspersed in some periods. Evaporation makes the water bodies shallower, and the concentrated brine starts to precipitate salt under the arid and hot climate conditions. Redox proxies indicate that most of the samples were deposited in relatively oxic conditions. The Sr/Ba ratios (average of 0.5) and paleosalinity (average of ∼35‰) during the depositional period indicate an increase in terrigenous freshwater input and carry of clasts into the evaporation basin. Furthermore, the freshwater supply enhances the hydrodynamics; as a result, the detritus that deposited in the early stage is broken into mud-clast conglomerates and co-deposited with the salt rocks. The results provide a geochemical basis for further study of mud-clast conglomerates in the Simao Basin and supply recommendations for the origin of salt deposits in similar basins around the world.