An abrupt change in sedimentary processes occurs in the alluvium of the San River headwaters in the Bieszczady mountains, Polish Eastern Carpathians. Older gravels are overlain, with a sharp boundary, by an extensive cover of sand and silt, which is enriched in wood debris, partly burned, at the base. The spatial distribution of the fine-grained alluvium, the wood debris composition and radiocarbon ages are best explained by a relatively sudden onset of deforestation and cultivation of the valley bottom and slopes in the middle of the second millennium. This corresponds well with palynological, archaeological and historical data on the agricultural colonisation of the valley. (C) 2002 Elsevier Science B.V. All rights reserved.
