Compositional variability of Saalian till in The Netherlands and its origin

Variations in composition between and within Saalian till types of The Netherlands are demonstrated with reference to grain-size distribution, fine-gravel petrography and heavy-mineral composition. Several factors explain different aspects of the compositional variations. Firstly, a compositional layering results from differences in the amount of local material that has been assimilated in successive till hands. Secondly, a petrographic stratification is present in the erratic components, which is most strikingly expressed by the occurrence of flint-poor till overlying till rich in flints. This feature is interpreted to have been inherited from an englacial debris stratification which is related to the distribution of source rock types in the up-glacier area. Finally, a predominantly lateral variation in till composition is present, reflected best in the assemblages of the indicator pebbles, resulting from deposition by ice streams of different source and direction of flow.