Abstract
Through a detailed study of the Pliocene Outcrops in the St-Péray valley we can identify, owing to their recurrent position beneath granitic slopes and also to their sinuous lay-out on a map, and old prepliocene riverbed of the Rhône from St-Péray up north down south to St-Georges-les-Bains. Besides, numerous outcroppings of rhodanian pebbles show that the river once again took that bed during the Villafranchian then the Giinz periods, heaping up during the latter a powerful, 40 meter high accumulation-sheet, prior to giving up that valley entirely while it was being hollowed out and the western river branch first met, further down south, the Charmes granitic threshold. The St-Péray depression thus became a two levelled dead valley of the Rhône : the higher one reaching up to 195-200 m and, the lower one to 170-180 m, both deeply weathered during the interglacial Günz-Mindel period (paleosoil ≥ 4-5 m) ravined and fossilized during the Mindel by siliceous local alluvia on the western side (Massif Central), by calcareous ones on the eastern (Crussol's Hill).
Published Version
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