The geoarchaeology of Mesolithic settlement and subsistence in the Muge valley, Lower Tagus Basin, Portugal

This paper presents the first results of geoarchaeological and palaeoecological investigations of Holocene environmental change in the lower reaches of the Muge valley, a small east bank tributary of the Lower Tagus river, Portugal. The Muge valley features several large and well-preserved mid Mesolithic shell midden sites, including the well-known sites at Moita do Sebastiao and Cabeco da Amoreira (e.g. Roche 1972). Archaeological research has long assumed that tidally-influenced valley floor environments in the immediate locality of the Muge middens provided a rich food resource for local Mesolithic communities (e.g. Zilhao 1993). To date, however, there has been little attempt to evaluate palaeoenvironmental records of contemporary environments and their subsequent changes. We demonstrate that the presently canalised, intensively cultivated and low-relief Holocene valley floor of the lower Muge is locally infilled with at least 11m of fine-grained alluvium and peat with good pollen, macrofossil and foraminiferan preservation. Sediments in the upper 1m of this sequence post-date e. 2200 BP and bury early-mid Holocene land surfaces contemporary with local Mesolithic occupation on the adjacent terraces. Preliminary pollen and foraminiferal analysis of alluvium deposited between c. 7500-2200 BP demonstrates the transformation of an estuarine saltmarsh environment to freshwater alder woodland around 2200 BP (dates quoted in this paper are given in radiocarbon years BP). The alluvial record of the lower Muge offers a rare opportunity to elucidate the changing environmental context and potential resource base of Mesolithic communities in the Muge valley.