Glacial-interglacial cycles in the Western Alps (Middle Durance Valley, France): sedimentary evolution and responses of continental surfaces

The existence of glacial cycles in the Alps was proposed as early as the first half of the 19th century following the observation of numerous direct traces left by glaciers in lower parts of alpine valleys. However, the influence of glacial-interglacial cycles on sediment transfer from the internal source zone to the peripheral mountain range is only now being re-investigated in the context of the recent “Source to sink” approach.

The study, part of the DYMODU project (2023–2026), a collaboration between the CNRS and the RGF focuses on new geological, geomorphological and geochronological investigations undergone in the Laragne-Montéglin depression and along the Middle Durance (western Alps, France). The DYMODU project aims at deciphering the role of glacial-interglacial cycles in both the landscape organization of alpine valleys and the evolution of routing systems during the Quaternary. The sediment pile shows a characteristic sedimentary motif repeated four times, indicating a succession of four aggradation-incision cycles. The sedimentary motif records a period of aggradation during which a several tens of metres thick conglomerate fills one or more palaeo-valleys, affecting the underlying units. This conglomerate is topped by glaciogenic deposits (ground till, morainic vallum), then incised by one or more palaeo-valleys affecting the entire sedimentary series, often down to the underlying sediments before the onset of the aggradation phase of the next cycle begins, and fills these palaeo-valleys.

To confirm the integration of these cycles into the Quaternary evolution of the area, preliminary dating was carried out on various sedimentary morphostructures using Optically Stimulated Luminescence dating (OSL), Electron Spin Resonance dating (ESR) and Cosmogenic Nuclides (CN).

In this contribution, we will present the sedimentary pattern of a typical sequence. We will attempt to deconvolute the signals of the general Alpine uplift, the lithospheric flexure due to glaciation, and the glacio-isostatic rebound during deglaciation. This will enable us to discuss the interdependencies between climate and tectonics for valley glacier systems and the forcings that influenced sediment routing during the Upper Pleistocene in the Alps.