ORIGIN AND AGE OF THE LOWER BAVARIAN SAND-DUNES LANDSCAPE AROUND ABENSBERG AND SIEGENBURG

The Lower Bavarian aeolian sand areas and sand-dune landscapes in the Abensberg/Siegenburg area (county/Landkreis Kelheim, Lower Bavaria) originated in an area where the Late Tertiary deltaic sediments of the Ur-Naab are overlain by a complex system of Pleistocene Danube gravels as well as those of the Abens river, deposited by in parts widely-shifting Quaternary river courses, mainly during the Riss glacial. This explains the absence of any significant loess cover of the area. The sand dunes and aeolian sands occurring there have been known for a long time, and their mostly late glacial age origin can be stratigraphically inferred. During the Holocene there were repeated phases of aeolian remobilisation, each of them related to an overexploitation of the carrying capacity of the landscape. It can be excluded that remobilisation was caused by changing climate. Today the dune fields, up to 10 m high, have partly been set aside as nature reserves, or are being used for agriculture and forestry. Based on geophysical prospection, at four selected dune chains and their surroundings,a distinction has been made between the underlying aeolian sand sheet, the dune cores, and younger aeolian accumulation bodies, and they have been sedimentologically characterised. The dune sands have been dated by OSL, macro-remains and the humous material of fossilised soil horizons by the radiocarbon method. Forest clearing of much of the landscape began during the Neolithic period, related to the operation of a flintstone mine at Arnhofen. Two significant phases of sand dune growth have been dated to the Bronze Age and the High Middle Ages, largely determining the aspect of the present dune landscape. There is evidence of younger remobilisation phases up to the 1950s. With reduced settlement pressure, the dunes landscape returned to a phase of morphodynamic stabilisation without any evidence of directed reforestation or dune stabilisation measures.