Weathering mantles and their significance for geomorphological evolution of central and northern Europe since the Mesozoic

Weathering mantles (saprolites) are very widespread in central, western, and northern Europe, where they form thick near-surface residual deposits, often in excess of 50 m. They vary in the type of weathering, the bedrock lithology involved, the topographic setting, and the age and stratigraphic context. This review paper provides information about the distribution and major characteristics of weathering mantles from a number of ‘key areas’, including the British Isles, the Central European belt of mid-mountains and uplands, the Scandinavian Mountains, and the Fennoscandian Shield. It also examines the evidence for weathering (=etched) origin of various landforms, including boulders, tors, inselbergs, basins and some regional landforms assemblages. Major types of regionally important weathering mantles include ferrallitic (lateritic) saprolites, kaolinite-rich saprolites, sandy to grus mantles, and various residuals left after partial dissolution of carbonate rocks. Although dating of weathering mantles is often circumstantial, it appears sufficiently precise to argue for various ages of deep weathering. Mesozoic (pre-Late Cretaceous) mantles are particularly widespread, but there are also Early Tertiary and Miocene saprolites widely present, whilst most grus weathering is likely to be of Miocene to Pleistocene age. Individual upland areas have been subjected to multiple episodes of weathering, whose legacy is the present-day co-existence of different weathering products. Continental and shallow marine deposits around the uplands, particularly in the North Sea and intra-continental graben structures, are often dominated by quartz and kaolinite, pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale. They demonstrate that weathering mantles repeatedly formed and were subjected to erosion, and new cycles of weathering were initiated. We suggest that deep unroofing of basement structures in many parts of Europe has been mainly accomplished by deep weathering and stripping of pre-weathered rock. The phenomenon of deep weathering has been very important for geomorphology. Etched landforms vary in size, from small residual boulders up to regional characteristic landscapes (etchsurfaces), such as joint-valley landscapes of southern Sweden or undulating multi-convex and multi-concave landscapes of many uplands in central Europe. Deep weathering has played a major part in the geomorphological evolution of Europe since at least the Late Triassic, and the concept involving long-term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features.