Ostracod evidence for the Neolithic environment of Rio Sizandro, Portugal

Abstract

Boreholes made to investigate the Neolithic occupation of the Rio Sizandro, western Portugal, were analysed for ostracods and associated micro-biota. Two boreholes in the middle reaches of the valley, near the village of Benfica, provide evidence of brackish estuarine conditions during the interval 6,500–6,200 cal BP of the late Neolithic followed by a decline in palaeosalinity towards freshwater conditions. Following the high-stand of eustatic sea level at about 6,500 cal BP, and possible formation of a coastal sand barrier, the influence of the rivers in the hinterland became predominant with dramatically increased erosion and sediment supply to the river valley, with consequent westward movement of marine conditions to the modern coastline.