MESOZOIC TERTIARY WEATHERING AND SOIL FORMATION ON SLATES OF THE RHENISH MASSIF, GERMANY

Weathering of Paleozoic slates and sandstones of the Rhenish Massif in western Germany, which occurred during the Upper Mesozoic and Tertiar y under warm, humid tropical to subtropical climatic conditions, led t o the formation of a regolith up to 150 metres thick. In flat upland a reas of the Hunsruck and Eifel, where the tectonic uplift was relative ly weak, remnants of this weathering mantle, more or less truncated by Upper Tertiary and Pleistocene erosion, are still preserved. On overl apping sections and drill cores of an autochthonous paleosoil and the saprolite underneath, the morphological, geochemical and mineralogical zonation of a complete profile of the weathering mantle has been reco nstructed. A fossil pre-Oligocene Plinthitic Acrisol, covered by Oligo cene fluvial sediments, displays characteristics formed under a high g roundwater table. On the other hand the underlying saprolite can be su bdivided into a lower reduction horizon and an upper oxidation horizon , each of them more than 40 meters thick. This indicates a polygenesis of the weathering mantle during the Tertiary, due to descending groun dwater tables caused by the beginning tectonic uplift of the Rhenish M assif and drier climatic periods during the Middle Tertiary. During th e Upper Oligocene the deposition of kaolinitic clays derived from remo ved horizons of the kaolinitic soils started in fault-block depression s. Periglacial processes during the Pleistocene led to a further remov al of the weathering mantle and to the deposition of superficial layer s on top of the autochthonous remnants of the saprolite. Presently the kaolinitic sediments as well as the saprolite are exploited as kaolin deposits.