Archaeological and radiocarbon dating of alluvial fans as an indicator of prehistoric colonisation of the Głubczyce Plateau (Southwestern Poland)

The development of agriculture accelerated soil erosion processes and the deposition of erosion products in the form of alluvial fans at the mouths of dry or temporarily drained valleys. The age of the alluvial fan in Borucin, in the Psina basin, has been established and the stages of its formation have been reconstructed with the use of radiocarbon dating of the roof of peat underlying the mineral sediment of the fan. The fan started to form in the second part of Suboreal period (3650 š 70 BP). Maximum fan progradation occurred at the end of the Period of Roman Influence when the area was settled by the agricultural Przeworsk culture( 1670 š 70 BP). In the Early Middle Ages, silty clays eroded from cultivated slopes no longer reached the outer fan zone, which points to a lower population density/less intensive agriculture in the area. The period of formation of the second fan under examination, located at the mouth of a side valley of the Odra, has been preliminarily determined on the basis of archaeological research. The progradation of this fan is probably related to the agricultural activity of the Lusitian Culture and forest clearances linked to the construction of a stronghold (9th-7th century BC).