Abstract: Sedimentary structure is one of the mainelements of sedimentology. And mud cracks, which belong to the exposure related
structures, have been interested by scholars. In this study, mud cracks in Akesai River and Dang River, Dunhuang, Gansu were
classified according to shape characteristics and edge features of the polygon. Geometric features were characterized and the difference
of forming mechanisms was discussed for different types of mud cracks. The results show that there were rectangular, circular, irregular,
duplex and edge-curl mud cracks in Akesai River and Dang River, Dunhuang, Gansu. Temperature, sediments properties, the
differences between the upper and the lower, the salinity and biological activity influenced the formation of mud cracks. Moreover,
rectangular mud cracks tend to develop on the slope formation which was uncomfortable. The argillaceous sediments overlying siltstone
was usually thinner in the typical edge-curl mud cracks. The process of the mud crack development is divided into initial stage,
cracking stage, separation stage, and buckling stage. In addition, duplex mud cracks may be used to help understand changes in
palaeocurrent and palaeoclimate.

Key words: mud cracks, geometric features, types, influencing factors, genetic mechanism, Gansu