Sedimentological characterization and origin of the deposits in a Holocene marsh (Vernier Marsh, Seine Estuary, France)

摘要

A 20 m thick core drilled in the Vernier Marsh allowed us the study of the Holocene infilling downstream the lower Seine valley. This core presents an alternation of peats and detrital deposits. These detrital deposits were sedimentologically characterized (e. g. grain-size, clay mineral, carbonate...) what allowed us to define three different units: (i) the core bottom presents a great proportion of sand, carbonate and smectite and no chlorite; (ii) the median part of the core presents chlorite and a great proportion of illite and si (iii) the core top presents chlorite and a great proportion of smectite and sand. These three units were the result of different sedimentary dynamics (i. e. material source and particle transport dynamic). The clay mineral contents used as indicators of the material source were compared to these of regional formations (i.e. loess, clay-with-flints, chalk and suspended particle matter) what enabled us to distinguish: (i) a continental supply resulting from the erosion of the watershed (i.e. loess) in the core bottom dated from the Boreal and in the core top dated from the Upper Subboreal; (ii) an estuarine supply in the median part dated from the Upper Boreal to the Lower Subboreal. The grain-size distribution principally indicated a particle transport by suspension in the entire core to which a transport by traction that occurred in coarse detrital deposits was added.