The Nei Mongol (Inner Mongolia) Plateau is one of the most important salt lake areas in China. Its trona deposits are well known in the world. The soda lakes spread mainly over the northern part of the Ordos Basin

the central part of the Eren Basin

the southeastern part of the Hailar Basin and the Badain Jaran Desert are generally several to several dozen square kilometers

and surrounded by sand dunes. The salinity of soda lake brines is 200–350 g/l

the pH values

9.09–10.67. The brines mainly consist of Na(K)

Cl

SO4

CO3

and HCO3 of the Na(-CO3-SO4-Cl) type. Trona deposits in soda lakes on the plateau always occur in “bull’s eye pattern” and are usually in two layers of natron

mirabilite

halite and trona interbedded with black mud containing much illite clay and some gayllussite

dolomite and calcite. Commonly

the soda lakes on the plateau were formed on the depressions from the beginning of early Holocene

but the trona deposits were mainly precipitated under the low temperature in Mid-Holocene (as proved by our freezing experiments and sporo-pollen analysis).