Discovery of Spheric Dolomite Aggregations in Sediments from the Bottom of Qinghai Lake and Its Significance for Dolomite Problem

Qinghai Lake is the largest inland saline lake in China.In order to search for the mechanism of dolomite formation,a sediment column with 25 cm long was collected from the bottom of the lake at approxmately 15 km north to the Erlangjian.It has been discovered that there is 2.2% dolomite in the sediments through the analysis of X-ray diffraction.Some researchers also reported a 10% dolomite content in the sediments.SEM images show that the dolomite take the shape of the spheric aggregations with the diameter of 1—2 μm,associated with the pyrite aggregations at the similar size.The characteristics of these dolomite and pyrite aggregations are very similar to those microbal origin of dolomite discovered in the modern high saline lagoons and tidal flats.This is the first discovery of this kind of dolomite in the inland lake with low salinity,which is high significant to search the mechanism of dolomite formation and to understand the famousdolomite problem.