River terrace sequences: templates for Quaternary geochronology and marine-terrestrial correlation

Abstract

Fluvial sequences, particularly terrace staircases, represent archives of Quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments, in particular, the global marine oxygen isotope record. Fluvial lithostratigraphical frameworks also provide contexts for records, from fossils and artefacts, of faunal evolution and human occupation; conversely, both records can be means of relative dating of riverine sequences. Three fluvial sequences are examined as case studies. First is the Severn-Avon system in the English Midlands, which has biostratgraphical evidence and an amino acid geochronology, together with marker inputs from three different glaciations. The Somme sequence of northern France, famous for its Palaeolithic artefact assemblages, again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess/palaeosols sequences. The fluvial terraces of the River Arun, the final case study, lack dating evidence but are interspersed within the Sussex raised beach staircase. Although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation, an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the Severn-Avon, whereas in the Somme they occur at the tops of sequences, beneath loessic overburden.