Holocene stratigraphic architecture of a Mediterranean delta and implication for sediment budget evolution: Example of the Rhône delta

Abstract

Deltaic systems evolve as a result of interactions between the hydroclimatic processes that occur in the catchment area and the coastal marine processes that reshape the coastline. The Holocene evolution of these environments is controlled by climate and anthropization, which are rarely considered in models of the evolution of deltaic systems. The Rhône delta has recorded the impact of climatic variations as well as the development and evolution of human societies over the Holocene period. This system underwent a post-glacial evolution controlled by global climatic warming punctuated by short periods of cooling, fluvial metamorphoses and a rapid marine transgression generated by the melting of the ice caps, followed by the initiation of delta progradation from around 7000 cal yr BP. Sedimentological and chronostratigraphic studies of 17 cores, supplementing an existing dataset on the deltaic plain and the prodelta, have enabled us to construct well-constrained stratigraphic correlations, making it possible to specify the spatio-temporal evolution of the Rhône delta. The variation in sedimentary fluxes was assessed for the different sequences identified, using 95 new core datings to constrain the sequential evolution of the different lobes. From the stratigraphic correlations on the delta and the estimated volumes of sediments exported out of the deltaic system, the total sediment volume between 11,700 cal yr BP and today is estimated at 126 billion m3. The variation of sediment fluxes has been adjusted according to the different phases of lobe progradation linked with the climate oscillations and the anthropic activity evolution during the Holocene. Taken together, these data highlight contrasting periods corresponding to the Roman period, the Little Ice Age and finally the ‘Anthropocene’, that can be compared to the main Mediterranean deltaic systems during the Holocene.