Holocene palaeoenvironmental evolution of the Ebro Delta (Western Mediterranean Sea) : evidence for an early construction based on the benthic foraminiferal record

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in The Holocene 26 (2016): 1438-1456, doi:10.1177/0959683616640048.Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the Late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal, and beach materials deposited between 7600 yr BP and >2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta-plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the 3 last 2.0 ka during the development of three different deltaic lobes under highstand sea40 level conditions. The results of the present study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.Drilling and coring was funded by the US National Science Foundation 686 grant EAR- 0952146. Work on the cores presented in this study was partially financed by the Formation and Research Unit in Quaternary: Environmental Changes and Human Fingerprint (UPV/EHU, UFI11/09) and HAREA-Coastal Geology Research Group (Basque Government, IT767-13) projects. It was supported by an IRTA-URV Santander fellowship to Xavier Benito through “BRDI Trainee Research Personnel Programme funded by University of Rovira and Virgili R+D+I projects” and the European Community’s 7th Framework Programme through the grant to Collaborative Project RISES-AM-, Contract FP7-ENV-2013-two-stage-603396