Evolución de la llanura aluvial del bajo Guadalquivir durante el Holoceno medio-superior. Geoarqueología y reconstrucción paleogeográfica de la vega de Itálica (Sevilla, España)

Abstract

Even before Italica was founded by the Romans at the end of the third century BC, this settlement maintained a close relationship with the morpho-dynamic evolution of the lower Guadalquivir river (SW Andalusia, Spain), especially with the lateral channel displacements. In order to reconstruct the palaeogeographic evolution of the alluvial area of Itálica during the second half of the Holocene, our research has focused on the study of the fluvial paleoforms and the alluvial soil-sedimentary sequence, with special emphasis on the analysis of the geoarchaeological records. Ancient maps and aerial photographs of various scales and diverse dates have been interpreted. Borehole cores and profiles, manually or mechanically opened, have also been done to obtain samples for laboratory tests of the representative floodplain soils and sediments. The chronologies provided by the archaeological record were completed with several radiocarbon dates. From these results we propose a possible solution at a local level to the traditional discussion about the existence and location of the ancient harbour of Italica; and for the alluvial plain as a whole, a double alternating palaeogeographic sequence trending to millennial-submillennial scale has been reached. The first one occurring controlled by hydrologic and climatic factors, modulated by a prolonged and extended human pressure on the basin, and showing a succession of four main stages characterized by the predominance of alluvial filling (4833-3206 cal BP; 3130-1989 cal BP; 1620 cal BP- XI century AD; and around the last 500 years), which are separated by periods of stability that favored alluvial soils formation; meanwhile, the second sequence presents short-time terms prone to riverbed design shifting (period prior to Late Bronze; Roman-republican era; central Middle Age), also separated by lengthy phases of morpho-hydrographic stability. In the latter case the main factor does not seem to be, as in the first of those, hydro-climatic shifts and land use changes, but rather the last small regional fluctuations of sea level that came with the second part of the Holocene.