Ys Valley: a submerged palaeoriver pattern in the Bay of Douarnenez (Brittany, France)

Interpretayion of the recent high-resolution survey, CANADOU 2000, in the Bay of Douarnenez (Finistere, France) allowed us to restore the morphology of the substratum and the sedimentary filling of the bay. The Brioverian and Palaeozoic substratum reveals a well-defined network of incised valleys as results of successive emergence stages of the Bay during the Quaternary. Valleys join in a westward-widened mean valley, called Ys Valley. The present-day sedimentary fill of the bay of Douarnenez appears mainly controlled by the Holocene rise and the consecutive highstand. It comprises fluvial and estuarine deposits filling up incised valleys and marine sedimentation extending out of the incised valleys.Original Abstract: L'interpretation de donnees de sismique reflexion acquises dans la baie de Douarnenez (Finistere) au cours de la campagne Canadou 2000 a permis la restitution de la morphologie du substratum et l'etude des remplissages sedimentaires. Le toit du substratum de la baie de Douarnenez revele ainsi un reseau de paleovallees, entaille lors de periodes d'emersion dans un soubassement sedimentaire brioverien et paleozoique. Au cours des derniers interglaciaires, les invasions marines repetees determinent la repartition des formations sedimentaires du domaine cotier, deposees successivement en conditions continentales, fluvio-estuariennes, puis marines.