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Abstract: Appraisal of Erosional Sequence Boundaries and Facies Successions in Periglacial Environment by Pseudo-3D Modelling

Gilles Lericolais, Serge Berne, Jean-Francois Bourillet, Ifremer, Jean-Paul Auffret, Pol Guennoc, Francois Guillocheau

Very high resolution seismic combined with swath bathymetry (EM1000) systems have been used throughout marine surveys to understand Plio-Pleistocene facies successions and bounding discontinuities in the English Channel palaeovalleys.

The seismic sequences were digitally interpreted and a selection of reflector points were used to construct a 3D Data Terrain Modelling. A geometric model is built by mapping the reflector boundaries. The 3D representation of the English Channel palaeovalleys (interpreted till now as the Channel river), obtained by gridding and smooth-surface fitting, allow us to acknowledge the infill of the valleys and in particular to point out the pre-Pliocene tectonic control at depth of the Hurd Deep and/to underline the impact of cold climate weathering processes.

The concepts of sequence stratigraphy allow the subdivision of the sedimentary record into depositional sequences bounded by unconformities. The unconformities are thought to have formed as a result of globally synchronous sea level changes and have been used to construct world-wide stratigraphic correlations. However, the recognition of eustatic sea level changes in cold climate environment is very difficult. This is due to addition of phenomena as glacio-isostatic sea level changes added to glacio-eustatic changes.

Such glacial phenomena (erosion and tidal ravinement of permafrost) were at the origin of the present shape of the English Channel, giving so a flat submarine landscape and relics of palaeofluvial courses difficult to interpret.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France