Siltation of river-influenced coastal environments: Respective impact of late Holocene land use and high-frequency climate changes

The aim of this study is to unravel the respective influence of land use and high-frequency climate changes on the siltation of a river-influenced coastal environment. An 8.4 m long sediment core was recovered in the Pertuis Charentais (western France). An accurate 14C Bayesian age model was developed to perform a depth to time conversion of high-resolution sedimentological data obtained on the core. Forest loss and precipitation changes that occurred on the related catchments were reconstructed from data gathered in the literature. A sharp increase in winter rainfall (1700–1750 AD) intensified erosion of catchments previously sensitised by increased forest loss (1640–1710 AD), which resulted in a massive supply of silt to the coast from ca. 1775 AD onwards. A review of articles reporting similar mud layers is also proposed. Depending on their age, some major phases of mankind migration history could be traced back, which confirms the predominant influence of human activities on the siltation of river-influenced coastal environments. We therefore propose to group these mud layers into the “Anthropogenic System Tracts”, in reference to widely used sequence stratigraphy nomenclature, and we suggest that it might help to identify a Holocene to Anthropocene stratigraphic boundary in coastal areas.

► We report the siltation of a bay in response to deforestation-conditioned soil erosion.
► High rainfall around 1725 AD resulted in the deposition of a 1 m thick mud drape.
► Similar events have been reported worldwide and attributed to human activities.
► We propose to group these mud layers into the Anthropogenic System Tracts.
► This new stratigraphic model could help to identify the start of the Anthropocene.