Soluble salt deposit in the Nihewan beds and its environmental significance

摘要

Observation and experimental analysis of soluble salt depositalong four profiles across the strata deposited in Nihewan paleolakebasin enabled us to recognize the nature and evolution stages of theNihewan paleolake and its significance in stratigraphical divisionand pa- leo-environmental reconstruction. The Nihewan paleolake wasat least a weak-saline to semi-saline lake and represents anintracontinental lake in the semi-arid region. The lower mem- ber ofsedimentary strata in the paleolake contains gypsum layer and gypsumlamellae. Soluble salt is mainly composed of SO~2_4 and Ca~2+ ions,representing a trend of the paleolake evolving into a stage ofsulfate lake. The upper member of the strata has predominantly Cl~-,K+, and Na~+ ions in soluble salt, indicating a starting developmentof the paleolake to chlorite lake, but no salt rock was deposited,indicating a drying trend of the area.