Genetic interpretation of a lower triassic paleosol complex based on soil micromorphology
Abstract Paleosols have been described from the Lower Triassic Bunter Sandstone of Germany since the mid-fifties and interpreted primarily on the basis of macroscopic features. In this study microfabric and composition (micromopphology) are used to determine in detail the origin and climate for one paleosol complex known as the “Karneol-Horizont”. It represents the stratigraphic boundary between the Middle and Upper Bunter Sandstone. The locality is situated on the southwestern edge of the Black Forest near the small town of Bonndorf. The complex is 3.3 m thick and consists of a lower caliche and an upper vertisol. The caliche might be polygenetic and is characterized by dolomite and massive silica replacements of carbonate, thus could be determined as a sil-calcrete horizon. Younger sediment was deposited on this caliche and a vertisol developed. It is fine-grained, purple colored and exhibits a large number of deep shrinkage cracks filled with coarser material. Both soils could have formed in a semiarid climate because the ranges of precipitation rates under which the two types originate do overlap. Thus, no change of climate is necessary to account for the different soils on top of each other but only differences in local hydrological conditions, slight geomorphological changes or different time span of pedogenesis. Soils very similar to the Triassic sil-calcrete horizon described here have been recently reported from the Kalahari Desert in southern Africa.