Abstract
Abstract. The Devonian slates and sandstones of the Rhenish Massif were subject to deep and intensive weathering under (sub)tropical climate conditions during the Cretaceous, the Paleogene and the Neogene, which caused the development of a weathering mantle (regolith) >100 m thick, consisting of kaolinitic saprolite and paleosols as well as correlated sediments. Especially the tectonic uplift of the Rhenish Massif and climate change during the Neogene and the Pleistocene led to a vast denudation of the weathering mantle. Only in less uplifted areas of the mountainous region did thick remnants of saprolites remain, and they were covered by Neogene sediments as well as Quaternary periglacial slope deposits. As the kaolinitic weathering products serve as raw materials for the clay industry, unique exposures are available in the Hintertaunus which offer impressive insights into the landscape development of the past ∼80 million years: the excursion proceeds from Giessen to Limburg and further south and southwest to the eastern and western Hintertaunus area. At site 1 near the village of Langhecke, characteristics and properties of the fresh, unweathered slates will be demonstrated. Excursion sites 2 and 3 are situated near the village of Eisenbach. In two open-cast clay mines, both a terrestrial and a semi-terrestrial saprolite from silt slate, covered by periglacial layers, are exposed. Properties and genesis will be discussed on the basis of morphological characteristics and mineralogical and geochemical analyses, as well as isovolumetric elemental mass balances. At site 4 a former basalt quarry near the village of Biebrich exposes a Paleogene Plinthosol above saprolite. The autochthonous paleosol was preserved below Upper Oligocene basalt tuff and periglacial layers. Site 5 is situated within a huge pit for mining of Upper Oligocene to Miocene quartz gravel near the village of Wasenbach. A Miocene Plinthosol developed from alluvial sediments on top of the gravel beds and was covered by periglacial slope deposits. At nearly all sites the basal layers of the periglacial cover beds consist of kaolinitic paleosol/saprolite material, which has an important influence on the site properties of the Holocene soils.
Highlights
The bedrock areas in mountainous regions of Middle Europe, which was a continent during the Mesozoic and Tertiary, were subject to deep weathering undertropical humid climate conditions, which caused the formation of a kaolinitic weathering mantle tens to hundreds of metres thick, consisting of a paleosol above saprolite (Fig. 1)
The strong uplift during the Quaternary and periglacial conditions during the cold periods strongly supported the removal of the weathering mantle and led to the expansion of a sequence of periglacial layers above the truncated weathering mantle (Felix-Henningsen et al, 1991; Sauer and Felix-Henningsen, 2006, Fig. 2)
Requadt (1990) concludes that the Vallendar gravels were originally deposited as sediments of a Middle to Upper Oligocene (33–30 Ma) marine transgression advancing from the Mainz basin in the south of the Rhenish Massif towards the north
Summary
Unter (sub-)tropischen Klimabedingungen während der Kreidezeit, sowie im Paläogen und Neogen, waren die devonischen Schiefer und Sandsteine einer intensiven Verwitterung ausgesetzt durch die eine > 100 m mächtige Verwitterungsdecke (Regolith) aus kaolinitischen Saprolitzonen, Paläoböden und korrelaten Sedimenten entstand. Nur in den schwächer gehobenen Gebieten des Mittelgebirges, wie im Hintertaunus, blieben mächtige Reste der Verwitterungsdecke erhalten, die von neogenen Sedimenten und quartären periglazialen Deckschichten überlagert wurden. In zwei Tongruben sind ein terrestrischer und ein semiterrestrischer Saprolit aus Schluffschiefer aufgeschlossen, die von periglaziären Deckschichten überlagert werden. Am Standort 4, nahe der Ortschaft Biebrich, ist in einem ehemaligen Steinbruch ein autochthoner Plinthosol aus dem Paläogen aufgeschlossen, der unter oberoligozänem Basalttuff konserviert und von gegliederten periglaziären Deckschichten überlagert wurde. Exkursionspunkt 5 befindet sich in einem großen Kiesabbau nahe der Ortschaft Wasenbach, in dem oberoligozäne – untermiozäne Quarzschotter und -sande des Vallendar-Flusssystems abgebaut werden. Deren Basislage besteht hier, wie an den anderen Standorten, aus dem kaolinitischen Substrat des unterlagernden Saprolits/Paläobodens und hat damit einen bedeutenden Einfluss auf die Standorteigenschaften der holozänen Böden
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