Quaternary evolution of a large alluvial fan in a periglacial setting (Crau Plain, SE France) constrained by terrestrial cosmogenic nuclide (~(10)Be)

摘要

Located in the foreland of the Western Alps, the Crau Plain was the outlet of the Durance River in the Pleistocene. In order to constrain its geodynamic evolution in terms of chronology and denudation rates, the two main Quaternary deposits of this plain have been studied based on cosmogenic nuclide ~(10)Be concentration measurements along depth profiles. The abandonment of the Miramas and Luquier alluvial surfaces occurred at the beginning of glacial periods, Wiirm (isotopic stage 4) and Riss (isotopic stage 6), respectively. Discrepancy in denudation rates under similar geomorphological and lithological conditions suggests different denudation processes during glacial and interglacial periods. The denudation rate has been estimated at about 25 mm ka~(-1) for the interglacial period and about 60 mm ka~(-1) for the glacial period. The abandonment of the Crau Plain as the outlet of the Durance River occurred sometime between 75 and 35 ka.