The interplay of eustasy, climate and human activity in the late Quaternary depositional evolution and sedimentary architecture of the Po Delta system

摘要

The late Pleistocene and Holocene environmental evolution and sequence stratigraphic architecture of the Po Delta region. Northern Italy, are examined. The study units record the depositional evolution from lowstand continental accumulation to marine transgression and highstand progradation. Interpretation of the high-resolution, three-dimension geological mapping of the central Po Delta area was framed within the evolution of the whole of the delta region, stretching from Venice Lagoon to the South of Ravenna. The development of the delta lobes was correlated with the fluvial drainage history. A discussion on the different auto and allocyclic mechanisms controlling the depositional evolution and a quantitative estimation of the changing depositional rates are also provided. Outcrop study was based on field surveying and on the analysis of aerial photography, topographic micro-relief, historical cartography, archaeological and historiographic data. Subsurface analysis was based on stratigraphic coring and cone penetration testing. During the last glacial lowstand, the modem coastal region was the site of middle alluvial plain sedimentation. Deglaciation and early transgression were associated with an erosive disconformity development. In the modern coastal area, transgressive accumulation started between 10 and 9000 yr BP. Back-stepping fluvial and brackish marsh deposits were followed by delta-estuarine sand bodies, influenced by the last important eustatic rise pulses. Transgression climaxed at about 5500 yr BP, during a warm climate phase. Early highstand saw the growth of large sand spits and barrier islands, progressively turning the previous bays into confined lagoons. At about 3500-3000 yr BP, a particularly active meteo-marine regime profoundly affected the depositional dynamics. Etruscan and Roman times were characterised by a warm climate and by riverine stability associated with the development of a large delta lobe. At around 1500 yr BP, transition toward moister and cooler conditions and the abandoning of the Roman Empire hydraulic works coincided with important drainage network instability. The modem delta lobe was induced 400 years ago by an artificial fluvial-mouth cut. The early evolution of the lobe recorded very high accumulation rates. The modem fragile environmental situation is characterised by strong coastal erosion and difficult management.