青海湖底沉积物中球状白云石集合体的发现及其地质意义

青海湖为盐度低于海水的微咸水湖。为了探索白云石的成因，在青海湖二浪尖以北约15 km的湖底采集了长25 cm的沉积物柱状样品。对样品所做的X-衍射矿物物相定量分析表明其中含有2.2％的白云石。文献中也曾报道青海湖底沉积物中含有高达10％的白云石矿物。对这些含白云石矿物的湖底沉积物所进行的扫描电镜研究发现了其中呈球状、椭球状，大小1~2 μm的白云石集合体及其伴生的草莓状黄铁矿的存在。其特征与文献中报道的现代近海高盐度泻湖和萨勃哈中发现的微生物成因的白云石极为相似。这是内陆低盐度环境中此类白云石的首次发现，对于探讨不同盐度环境中白云石的形成机理，促进“白云石问题”的深入研究具有重要的理论意义。

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 famous"dolomite problem".