Abstract: Based on comprehensive analyses of color, sedimentary structure, particle size and thin sections for 600 meters cores, this
paper analyzed the sedimentary characteristics of beach-bar in the Zhahaquan area, Qaidam Basin, studied the distribution and origin
of the beach-bar in the sequence stratigraphic framework, and finally established the beach-bar sedimentary model. Results show that
the single sand body of beach-bar is thin in the Upper Ganchaigou Formation. There are many typical sedimentary structures formed
by wave action in beach-bar. The probability accumulation curve of particle size is mainly composed of two population: jumping and
suspended types. The bar is mainly developed in the large accommodation space of medium-and long-term base level cycle, and mostly
distributed in the large accommodation space of rising half cycle of short-term base level cycle. The beach is mainly developed in the
small accommodation space of base level cycle. The formation of the beach-bar is related to the accommodation space and the
sedimentary hydrodynamic conditions. Under the condition of high accommodation space, the water body is deep and the lake area is
large, which is favorable for forming large lake waves and lake flows. As such, the bar is developed. According to Walter’s law, the
sedimentary model of the Upper Ganchaigou Formation is established in combination with vertical variation of sedimentary types in a
medium- to short-term base level cycle.

Key words: Walther's law, beach-bar, Qaidam Basin, facies model, accommodation