Resumo
The Tagus estuary is one of the biggest LARGER estuaries of Europe (area of c.325km2). Lisbon, is located in the northern margin of the Tagus estuary and despite the long diachrony of its occupation since the Palaeolithic, the city was founded during the Iron Age and grown continuously since then. The riverine front, CONTAINING ARCHAEOLOGICAL evidences of occupation since the Iron Age, and clearly modified during the Roman Period, was successively enlarged at the end of the Middle Age by the construction of landfills, conquering DRY-LAND area TO the river THAT WAS USED SINCE THEN for the development of maritime activities.In 2014 a 7.5m-LONGcore was collected FROM SEDIMENT below the landfill (-1m MSL) during the re-arrangement WORKS of Ribeira das Naus (a Lisbon downtown riverine street built-up on a landfill constructed in the 1940´s). Several environmental proxies, combined with 14C dating, were analyzed at vertical high resolution. The sediment is essentially composed by mud (>90% of fine particles) with c.9% of organic matter and c.4% of CaCO3. d13C values are around -25‰, reflecting estuarine conditions. Sediments have accumulated between 2000 cal BP and 1362 cal BP, evidencing high sedimentation rates (SR) in this area during the Roman Period. Srwere extrapolated using Clam 2.2 software and values of 0.9 cm.yr-1 (-8.5m to -5.7m MSL; 2000 cal BP to 1600 cal BP) and 1.9-2cm.yr-1 (-5.7m to -1m MSL; 1600 cal BP to 1362 cal BP) were determined. The high sedimentation rates can RESULT from both natural and anthropic causes; however, according to Vis et al. (2015) the changes on the sedimentary pattern of the Tagus estuary over the last 2000 years are mainly due to human impact. The pollen record preserved in the core attests the existence of open landscape vegetation between 2000 cal BP and 1362 cal BP with the occurrence of heath and widespread of anthropogenic taxa. The inexistence of sediments younger than 1300 cal BP above -1m MSL could be related with dredging of the area for maintenance of the maritime activities or due to the lack of accommodation space in this low intertidal area.