Late Holocene sedimentary changes in floodplain and shelf environments of the Tagus River (Portugal)

Sedimentary changes during the last similar to 2500 years have been reconstructed from cored sedimentary records from the deltaic floodplain of the Lower Tagus Valley and the Tagus mudbelt on the continental shelf offshore Lisbon. We used a multi-proxy approach consisting of sedimentology, grainsize, pollen data and magnetic susceptibility. In the floodplain grainsize coarsened and sedimentation rate and magnetic susceptibility increased during the late Holocene due to an increased flooding frequency and/or intensity. On the Tagus shelf the mudbelt grainsize fined, together with a higher sedimentation rate and increased magnetic susceptibility. The fining grainsize is explained by an increased suspended sediment flux towards the shelf and subdued winnowing. Floodplain and shelf records were correlated by radiocarbon dating and changes in sediment characteristics. We identified four depositional phases (similar to 2300/similar to 1600/similar to 1100/similar to 670 cal BP) on the floodplain and the shelf. These are tentatively explained by land-use changes in the Tagus catchment. (C) 2009 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.