Abstract: Huge thickness of lake facies deposit of Quaternary is developed in eastern Qaidam basin, in which the abundant microfossils such as ostracods, charophytes and gastropods are important evidences for analysis of stratigraphy and sedimentary environment. According to the abundant stratigraphic and palaeontologic information of Quaternary in Well Cha-7, Ilyocypris assemblage zonation, Gastropods assemblage zonation and Charophytes assemblage zonation from up to down can be divided into of this well, and can be well correlated with the ones of Well Chadi-2, Chadi-3, Chadi-4, Chadi-5 and Chadi-6 around it, hence they take an important part in stratigraphic division and correlation in this area. Moreover, the paleoecologic significance of these zonations is consistent with the environmental significance in petrology and geochemistry, for example, the content of Cl-is fall rapidly but the value of TOC is relatively high in interval with Ilyocypris assemblage zonation, indicating a sort of sedimentary environment symbol adjacent to bayou where freshwater organism is developed. In background of drying palaeoclimate in Quaternary, a short-term development of freshwater biota such as ostracods and charophytes is resulted from the effects of local tectonic movement on the sedimentary environment.

Key words: Qaidam basin, Quaternary, paleontology, assemblage, sedimentary environment