Abstract: The upper member of the Lower Ganchaigou Formation in the Yingxi area, southwestern Qaidam Basin, is a set of evaporitebearing
lacustrine series. Pate of thin section, cores, drillings logging as well as geochemistry were systematically used to study the
characteristics of sedimentary cycles of the series in this paper. Results show a zonal distribution of evaporites to mixed carbonate rocks
and to clastic rocks from the center to the margin of the basin laterally. Vertically, two third-order sedimentary cycles and six
fourth-order sedimentary cycles were developed. Sedimentary cycles of all the levels are asymmetry with rapid transgression and slow
regression. Five types of lithofacies combination of evaporites were identified. Evaporites were formed by evaporitive crystallization
under a certain depth of lake water during regression, when there was an arid paleo-climate and rapid subsidence of the basin basement.
The development model of sedimentary cycles in the study area is established accordingly.

Key words: southwestern Qaidam Basin, Yingxi area, the upper member of Lower Ganchaigou Formation, evaporites, salt lake, sedimentary cycles