Abstract: In Sanxi river area of Changle of Fujian province, there are some pits developed in granitic rock on the top of mountains and the surface of river beds. Such pits known as mountain top glacial potholes or river valley glacial potholes have been considered to be typical glacial potholes, which were used to support the evidence that the Quaternary glacier has been extended to the area of Fujian Province, China. The field investigation for these pits we made in March 2011 shows that the pits are weathering pits or river potholes, instead of glacial potholes. In this paper, the origin and formation process, as well as the related influencing factors, of the weathering pits and the river potholes developed in this area were studied and compared from the aspects of geomorphology, sedimentology, petrochemistry and mineralogy. The studies show that the formation of the river potholes is due to the mechanical erosion of stream water while that of the weathering pits on the top of mountains has nothing to do with river water but is the water standing in rock surface depression that results in chemical weathering. The weathering pits may also be found in river valleys, but can be only developed in the positions where the river water could not be reached after a river incision. The potholes and the weathering pits are morphologically distinct with particles of different roundness and grain sizes, denoting the different formation processes generated by chemical weathering or mechanical erosion. The different CIA values and the different quartz to feldspar ratios between the particles in the weathering pits and the rock where the pits were formed could be used to indicate the results of chemical weathering and mineral differential weathering. The river potholes also have different CIA values or quartz to feldspar ratios between the particles and the rocks as the weathering pits, and then the value and the ratio could not be used to distinguish the potholes from the weathering pits. However, the river potholes have a chemical element migration between the rocks and the particles, which is very different from that of the weathering pits, reflecting the processes of the particle transportation by river water in the potholes and the chemical weathering in the weathering pits.

Key words: weathering pit, stream pothole, granite, Sanxi River, Pingshan Mountain