Berné, Serge Pierre¹
(1) IFREMER, Plouzane, France

ABSTRACT: Architecture of the Rhone Subaqueous Delta: Stepped-Sea-level Rise and Avulsions

The Rhone subaqueous delta was revisited using high resolution bathymetric and seismic methods. The new data set reveals a complex morphology with preserved features linked to the deglacial history of the delta. The preserved retreat path of the delta indicates that some distributaries directly fed canyon heads during the last Glacial. Incised meandering channels within the main canyon courses are indicative of such direct connection. Channel-levee like features are observed on the outer shelf, and are buried under the HST on the inner shelf. Transgressive parasequences are associated to slow-down of sea-level rise, but most of lobate depocenters are linked to avulsions of the highstand (<7ky) river, and can tentatively be tied to deltaic lobes mapped onshore. Long (15m) piston cores allow us to "ground-truth" key surfaces detected on seismic data, and to date the onset of sea-level rise. Paleo-shorefaces are preserved at about 50 m water depth. They display sandy clinoforms that grade seaward into clayey silt with interbedded silty sand beds (storm beds and/or flood deposits). The upper part of these shelf sand bodies was reworked into transverse dunes that are presently inactive. The modern delta front of the Grand Rhone exhibits subaquatic channels that could be formed by high density currents during floods.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.