Derivation of the chalk superficial deposits of the North Downs, England: an application of discriminant analysis

Stepwise discriminant analysis was used on particle size and heavy mineral data from 276 sediment samples, including 39 from published sources, to distinguish between Palaeocene and Plio–Pleistocene deposits, found above the Cretaceous Chalk in southeast England, and to determine parent materials of the soils and superficial deposits of the central North Downs. Of 71 known cases (in situ deposits), 85.9% were correctly classified using textural data (sig. 99.9%), and 89.7% of 29 known cases (sig. 99.9%), using heavy mineral data. The best textural discriminating variables were %sand, graphic mean, %clay and graphic skewness, and the best heavy mineral discriminants were %kyanite plus staurolite, %andalusite and %garnet. Discriminant analysis has achieved good differentiation between marine Plio–Pleistocene sands, Clay-with-flints, loess and Palaeocene groups, and allowed objective classification of sediments of unknown origin. The distribution of parent materials revealed, strongly upholds the earlier interpretation Z. Geomorphol. 39 (1995) 433] that in the central North Downs, except where Palaeocene residuals survive, the superficial cover above the Chalk consists of in situ Clay-with-flints sensu stricto, beneath Plateau Drift and loess. Clay-with-flints is seen as residual, and Plateau Drift as a Pleistocene soliflucted deposit. Textural affinities of Reading Beds Clay and Clay-with-flints elicited by a third discriminant analysis, using additional published data from 22 samples, suggest their common derivation from Chalk residua.