A new interpolation method to measure delta evolution and sediment flux: Application to the late Holocene coastal plain of the Argens River in the western Mediterranean

Résumé En

Rapid environmental changes along the Mediterranean coasts influenced the sedimentary dynamics, shoreline position and human settlements in deltaic areas over the last millennia. An innovative and multiproxy approach using geostatistical modelling was developed to estimate geomorphic evolution and sediment fluxes in deltaic areas, while palaeoecological conditions and environmental changes were assessed from geochemistry and cluster analyses of molluscan fauna. This method was applied to the coastal plain of the Argens River (southern France) in the western Mediterranean. The study of facies associations led to the identification of depositional environments representative of prodelta, delta front, river channel, floodplain, marsh and abandoned channel. The late Holocene sediment flux in the Argens River bayhead delta ranged from 15,800 ± 2300 to 52,000 + 8500 m3.yr-1. The highest rates of sediment deposition and delta growth occurred between 2500 and 2000 cal yr BP during a period of high flood frequency in the western Mediterranean. A geomorphically-induced decrease in subaqueous sediment flux over the past 2500 years and an increase in fluvial activity from 1600 to 500 cal yr BP were primarily controlled by autogenic processes due to change in accommodation space, delta slope and tributary junctions. A sharp increase in subaerial sediment flux from 500 to 0 cal yr BP was probably driven by hydroclimatic change characterized by more frequent flooding during the Little Ice Age. High sediment fluxes and climate-driven fluvial activity were associated with a southward shift of the North Atlantic westerlies or a northward migration of the intertropical convergence zone.