Discrimination of particle zonation on a pebble beach



The extent to which pebble shapes are zonally sorted on a pebble beach is examined. On the basis of comprehensive point samples from a pebble beach in west Wales, and using factor analysis, a pebble shape index for each point sample is derived. It is proposed that the sum of squares (%RSS) explained by a linear trend surface of shape index values, approximates to the degree to which the second derivative of pebble shape with respect to distance downbeach, tends towards zero. If the second derivative is zero there is no zonation of sample shape values but, rather, a uniform trend. Strength of zonation on one beach is calculated for eight beach samples during 1971. A heterogeneity index (Ht) is introduced to show the degree of difference between clustered point samples on the basis of shape and size. On the basis of %RSS and Ht value, discrimination between pebble facies type on the sample beach over time can be made.