Authigenic carbonates extracted from the sediments of Lake Bayanchagan, Inner Mongolia were analyzed for X-ray diffraction, scanning electron microscopy, carbonate content and δ18O to reveal the process of precipitation of different carbonate fractions within the lake. The data show that the lacustrine sediments contain abundant carbonates. Calcite predominates the carbonate fraction between 12 400 cal.a B.P. and 6 000 cal.a B.P., and dolomite occurs after 6 000 cal.a B.P.Calcite. The dolomite grains are identical both in shape and in size to those of microbial origin reported in other studies, suggesting a key role of microbial activities in the formation of dolomite in Lake Bayanchagan. The appearance of dolomite around 6 000 cal.a B.P., which is consistent with changes in the carbonate δ18O and pollen assemblage, provides mineralogical evidence for the salinization of the lake, implying an increase in the regional aridity since the mid-Holocene.
