摘要
The shape of sedimentary particles contains information useful to recover the ancient sedimentary processes in which the particles were transported and eroded. The traditional method to obtain the grain shape property,such as the roundness,is to describe the property by comparing the grain shape to the images of standard particles. Different quantitative methods have been developed to describe the particle shape properties in the past decades. These methods in recent years have become easier to be operated with the development of computer morphological analytical techniques. In this paper,three quantitative grain shape indexes,the IPP roundness, Fractal dimensions and Fourier not roundness,were respectively used to measure the visual standard particles suggested by Powers and then sedimentary grains obtained in the field were used to examine if the three methods can be the tools replacing the traditional visual method in actual sedimentary application. The shape of particles in Powers visual standard chart were firstly detected by the three methods using a popular computer morphological analysis software,Image Pro Plus 6. 0 ( IPP) ,to find out if the grain classifications produced by such methods could match the Powers standard. And then the three methods were also used to measure the shape of the real particles taken respectively from the mountain top weathering pits and the stream potholes developed in a same hill,Matoushan Hill of Guangdong,to see if the particle shape indexes produced by these methods could be used to discriminate between the weathering pit grains and the stream pothole grains. The results of the analysis indicated that: ( 1) The Powers visual standard expresses the particle shape not only by the grain outline that is rounded or not rounded,but also by the grain surface texture; ( 2) the shape indexes of the three methods cannot totally match the Powers visual standard; ( 3) all of the three methods can distinguish the grains in a weathering pit from those in a stream pothole; ( 4 ) IPP roundness is better than the other two indexes to distinguish the particles produced by chemical weathering from those by river erosion if the surface texture of the grains is not excessively stressed; ( 5) the morphological analysis of the grains in the weathering pits and in the stream potholes shows the different origins of the pits and the potholes.
