A multivariate analysis of the particle size characteristics of regolith in a catchment on the darling downs, Australia

Abstract

A multivariate statistical methodology consisting of R- and Q-mode cluster analysis and Q-mode factor analysis is employed to examine the interrelationships between landforms, the particle size properties of the regolith, and the genetic geomorphic processes in the Linthorpe catchment in the Darling Downs district of south-east Queensland. Cluster analysis of randomly sampled regolith materials on the basis of their detailed particle size properties shows that the materials form both statistical and spatial clusterings (called here “textural groups”). Textural groups with geomorphic significance are recognizable at two hierarchical levels in the Q-mode cluster dendrograms, and indicate that the spatial variability of particle size can be envisaged as existing at two levels of scale. The three dominant geomorphic processes responsible for the spatial variability of particle size are identified from the results of Q-mode factor analysis of the same particle size data. The three principal factors are associated with suspended sediment transport and deposition, weathering, and bedload transport and deposition respectively. The precise nature of the downslope changes in particle size and in the relative amounts of the three inferred processes is revealed by the position, size and composition of the cluster analysis textural groups in the three factor space. Process-response models displaying these relationships at two levels of scale are constructed on the basis of the classifications derived at different hierarchical levels in the Q-mode cluster dendrograms. At the higher hierarchical level, zones upslope and downslope of the pediment head are dominated by weathering and surface transport factors respectively. At the lower level, four zones with distinctive process-response characteristics are recognised. In descending elevation from the drainage divide, a valley-side slope with all zones present, consists of (i) a residual zone, (ii) an erosional zone, (iii) an accumulation zone of fine textured colluvial and alluvial deposits, and (iv) a second accumulation zone of coarse textured infilled channel deposits.