Status: this preprint was under review for the journal SOIL. A revision for further review has not been submitted.
Isovolumetric replacement and aeolian deposition contributed to Terrae
calcis genesis in Franconia (central Germany)
Bernhard Lucke,Helga Kemnitz,and Stefan Vitzethum
Abstract. We investigated Terrae calcis on limestone and dolomite in Franconia, as well as the red fill of deep cracks in the rock (Karstschlotten). SEM images of the rock-soil transition zones supported by EDS found amorphous clays along fissures that could be products of metasomatic, authigenic clay neoformation within microfossils, calcite, and dolomite grains, or of replacing deposition of amorphous clays inside the calcite, probably due to percolating waters (illuviation). In the SEM-images, the replacement appears as exchange process characterized by substitution of Ca and Mg against Si, Al, and Fe. There is no crystalline clay deposited within rock fissures, and the transition between calcareous minerals and amorphous clay is gradual. This and the presence of Fe let it seem possible that plant roots play a major role for the transport of elements and neoformation of clays, similar to clay pavements along eucalyptus roots in Western Australia. In this context, more or less uniform Fe(d/t) ratios contradicting other weathering indicators could be the result of neoformed phyllosilicates containing Fe3+. Bulk soil and bedrock analyses indicate that the solum of the investigated Terrae calcis does mainly not represent insoluble bedrock residue. Dust deposition and bioturbation are evident due to sand grains coming from a loess surface cover, which buried pre-existing Terrae calcis and contributed to their substrate, apparently supplying quartz and clay-rich pseudosand aggregates.
How to cite. Lucke, B., Kemnitz, H., and Vitzethum, S.: Isovolumetric replacement and aeolian deposition contributed to Terrae
calcis genesis in Franconia (central Germany), SOIL Discuss. [preprint], https://doi.org/10.5194/soil-2017-4, in review, 2017.
Received: 16 Jan 2017 – Discussion started: 01 Feb 2017
There is no general agreement on the genesis of Cambisols on limestone (Terrae calcis), which limits the interpretation of these soils as environmental archives, in particular regarding the role of climate for their formation. We re-visited profiles of brown (Terra fusca) and red (Terra rossa) clays on limestone that had in the 1930s been suggested to have formed by metasomatism, and found that isovolumetric replacement of limestone by clay and aeolian deposition contributed to their genesis.
There is no general agreement on the genesis of Cambisols on limestone (Terrae calcis), which...