Grandes séquences et principales ruptures morphogéniques en Haute Provence : les complexes sédimentaires des petits organismes torrentiels de Moyenne Durance

Abstract

We quantify the Holocene Rhone delta evolution by the assessment of sediment vertical accumulation, horizontal progradation of the delta plain, and volumes of the sedimentary sequences. We use for this purpose a 3D reconstruction with a GIS program and as input data a géomorphologie map with high chronological resolution, many high resolution seismic profiles located in the internal platform, and some cores. The calculation of the volumes we obtain underestimates strongly the sedimentary storage if we refer to the usual quoted values. This is probably linked to the lack of cores onshore and in the shelf to calibrate the seismic fades, and also to the difficulty in assessing the porosity of sediments in the column. However the period 2800/2525 cal BP seems clearly identified as a period of fast sediment storage and deltaic progradation which could correspond to the climatic deterioration of the first Iron Age known upstream in the Rhone catchment area. The same trend appears also during the second Iron Age but with a lower impact. The antitetic apparent functioning of the Durancian upstream watershed with the contributions on the delta of the Rhône is to be noted, but the not exhaustive character of the quantification of the sedimentary accumulation on the internal continental shelf does not allow to confirm this hypothesis.