Accelerated transgressive processes in a Mediterranean coastal barrier: Subsidence, anthropic action and geomorphological changes since the Little Ice Age

Subsidence, changes in sediment supply and environments, sea storms, current sedimentary deficit and recent anthropic action are factors determining coastal geomorphological processes and evolution of a transgressive Mediterranean coastal barrier. At a longer timescale, the barrier landward migration is partially due to local subsidence of tectonic origin. Peatmarsh remains under seawater at around 100 m from the present-day coastline (4821-4566 and 4874-4820 cal BP) show evidence of the more advanced position towards the sea of the late Holocene coastal barrier, which has not been preserved. Furthermore, behind the present gravel barrier, wide sandy washover fans dating about 665 cal BP and 503 cal BP were deposited in the early Little Ice Age (LIA) and during the SpOrer Minimum, in periods when sea storms were highly frequent in the Western Mediterranean. The source of the washover fine sands was an ancient deltaic lobe of the Sant Miguel river southern palaeochannel. The avulsion towards the current northern mouth (ca. 1790) produced important sedimentary coastal changes, from fine to gravelly sands. More recently, gravelly washover fans indicating rollover processes were found in the 1945 barrier. Nevertheless, progradational sets of gravelly beach ridges were identified in the central sector between 1977 and 1997. Since 2003, overtop and overwash processes during storms have formed a steep beach ridge nearly 3 m high. Finally, recent direct anthropic action has favoured rapid landward migration of the barrier, with processes of fast rollover, cannibalization and dissolution phases.