Soluble salt deposit in the Nihewan beds and its environmental significance

Observation and experimental analysis of soluble salt deposit along four pr ofiles across the strata deposited in Nihewan paleolake basin enabled us to recognize the nature and evolution stages of the Nihewan paleolake and its significance in stratigraphical division and paleo-environmental reconstru ction. The Nihewan paleolake was at least a weak-saline to semi-saline lake and represents an intracontinental lake in the semi-arid region, The lower member of sedimentary strata in the paleolake contains gypsum layer and gy psum lamellae, Soluble salt is mainly composed of SO42- and Ca2+ ions, repr esenting a trend of the paleolake evolving into a stage of sulfate lake. Th e upper member of the strata has predominantly Cl-, K+, and Na+ ions in sol uble salt, indicating a starting development of the paleolake to chlorite l ake, but no salt rock was deposited, indicating a drying trend of the area.