Stratigraphie und Morphogenese von frühpleistozänen Ablagerungen zwischen Bodensee und Klettgau

Abstract. The stratigraphy and paleogeography of the Deckenschotter (“cover gravels”) of the Rhine glacier system between Lake Constance, the city of Schaffhausen and the Klettgau area (Switzerland, Germany) was revised. This was achieved by means of new surveying and mapping, petrographical analysis und a systematic evaluation of available literature and borehole data. Within the Deckenschotter three morphostratigraphic units can be discerned: (a) Höhere (higher) Deckenschotter, (b) Tiefere (lower) Deckenschotter and (c) Tiefere Deckenschotter, unteres Niveau (lower level). The topographically highest unit, the Höhere Deckenschotter, cannot be subdivided into lithostratigrafic units. The gravels classified as Tiefere Deckenschotter are grouped into two morphostratigraphical units; the altitude difference of the bases of both units is minor. They are, however, separated by an erosional discontinuity caused by a signifi cant rearrangement of the hydrographic network.The older one of the two units (Tiefere Deckenschotter) comprises sediments of at least two depositional phases, separated from each other by a hiatus. There are signs of temperate climatic conditions during the period of non-deposition. The tectonic analysis of the study area showed that in general the altitude of the Deckenschotter was not affected by post-depositional tectonic activity. A tectonic displacement of the Deckenschotter occurrences in the Hegau cannot be ruled out as their topographic position is unusually high compared to equivalent deposits further paleo-downstream. However, this does not affect the proposed morphostratigraphic subdivision. The Upper Rhine Graben system (tectonic lowering) controlled the hydraulic base level and the morphogenesis for both the Deckenschotter occurrences discussed here and those in central northern Switzerland. Therefore, the morphostratigraphic units of both regions can be correlated, even though the number of lithostratigraphic units does not match. In the Höhere Deckenschotter this could be ascribed to an incomplete sedimentary record or a lack of data; on the other hand, this might indicate that the connection Lake Constance – Upper Rhine Graben was established later than the connection Lake Walen – Upper Rhine Graben. In contrast, there is no simple morpho- or lithostratigrafic correlation with the early pleistocene deposits of the German Alpine Foreland, since they are oriented towards and controlled by the Donau river system.