Evaporite deposition since marine isotope stage 7 in saline lakes of the western Qaidam Basin, NE Qinghai-Tibetan Plateau

Abstract Evaporites were deposited in every saline lake in the western Qaidam Basin (QB) during the late Quaternary, but the role of the Quaternary glacial environment in the formation of evaporite deposits remains to be clarified. In this paper, five upper Quaternary evaporite-bearing profiles in the western QB are studied. Uranium-thorium (U–Th) dating was applied to obtain the depositional ages of these profiles, and X-ray powder diffraction (XRD) analysis was applied to identify the evaporite minerals. The U–Th dating results indicate that halite (NaCl)-dominated profile D08 and mirabilite (Na2SO4·10H2O)-dominated profile MXK were deposited between 146.1 ± 53.4 ka and 171.3 ± 27.2 ka, mainly corresponding to Marine Isotope Stage (MIS) 6; the bloedite (Na2Mg(SO4)2·4H2O)-dominated profiles WMX1 and WMX2 were deposited between 182.1 ± 2.5 ka and 206.7 ± 7.0 ka, mainly corresponding to the late period of MIS7; and the mirabilite and halite-dominated salt layers in profile D30 were deposited between 9.0 ± 0.7 ka and 14.3 ± 1.6 ka, with mirabilite deposit ages corresponding to MIS2 and early MIS1. The minerals in the profiles identified by XRD analyses are mirabilite, thenardite (Na2SO4), bloedite, gypsum (CaSO4·2H2O), starkeyite (MgSO4·4H2O), hexahydrite (MgSO4·6H2O) and halite. This study, combined with those of previously reported evaporite deposits in the western QB, indicates that MIS7, MIS6 and MIS2 were important evaporite deposition periods in the late Quaternary. Evaporite depositions in the QB during MIS6 and MIS2 were attributed to a decrease in temperature and shrinkage of the saline lake hydrosphere. The cold glacial climate during MIS6 and MIS2 was conducive to mirabilite deposition in the western QB, while the relatively warm climate of the late period MIS7 was conducive to bloedite deposition.