--> Abstract: Relationships Between the Morphology and the Infilling of Incised-Valleys: The South Armorican Example (Western France), by David Menie and Jean-Noel Proust; #90039 (2005)

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Relationships Between the Morphology and the Infilling of Incised-Valleys: The South Armorican Example (Western France)

David Menier1 and Jean-NoëL. Proust2
1 Université de Bretagne Sud, Vannes, France
2 Géoscience-Rennes-1, Rennes, France

The recent acquisition of 3000 kms of high resolution seismic and morphobathymetric EM1000 data along the inner part of the Bay of Biscay shelf provides new information on relationships between the infilling of the Pleistocene and Holocene incised-valleys and their geomorphologic evolution. The incised-valleys run parallel and perpendicular to the modern mixed-wave and tide dominated coast. The valleys are both a submerged at the coast between 0 and 70 m depth, and emerged on land. The depth of their basal incision wedges out seaward from 30 meters on land to nothing at 50-70 meters of water depth. Their width varies from 200 to 4000 meters with three kinds of transverse sections: rounded base V shaped sections, flat-based U-shaped sections and stepped-sections with morphologic terraces. The longitudinal profiles of the talwegs of the valleys exhibit abrupt changes in slope that superpose to major regional faults. The valleys are filled up by marine and fluvial sediments organised in facies belts that have been carefully mapped. These maps show that sediment thicknesses and facies belts distributed along the talwegs of the valleys relate to the morphology of the underlying incision (morphologic terraces). The facies belts change when valley width decreases, valley depth increases and secondary channels merge at recently reactivated old basement faults. It seems that tectonics plays a significant role in controlling the morphology of valley incision but the nature and the geometry of their infilling is certainly also driven by climatically-controlled sea-level changes.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005