Channel Architecture and Facies in a Sand-Rich Turbidite System, Eocene to Oligocene Western Champsaur Sandstones, SE France

Jamie Vinnels¹, Bill McCaffrey¹, Rob Butler¹, and Rufus Brunt^2
1School of Earth and Environment, University of Leeds, Leeds, United Kingdom
²Stratigraphy Group, University of Liverpool, Liverpool, United Kingdom

The preserved remnants of the Eocene to Oligocene Western Champsaur Sandstones in the Western Champsaur Basin of SE France are dominated by NE-dispersing sheet- and channel-form volcaniclastic turbiditic sandstones. The Champsaur Channel complex contains at least 3 axially persistent sand conduits. Presented is a description of the internal architecture and sedimentology of one such conduit, termed here the Borels Channel, thought to represent the most distal preserved section of the Western Champsaur Basin fill.

In this part of the basin, the Western Champsaur Sandstones are seen to onlap towards the NW onto bounding slopes composed of Eocene Nummulitic Limestones and Blue Marls. The Borels Channel is at least 1000m wide, is preserved up to 5km along its inferred axis and is seen to incise at least 50m into its substrate. Intra-channel sections are characterised by coarse to gravel-grade amalgamated units, while extra-channel sections comprise laterally extensive tabular sheet-form intervals of medium-grade sand and silt/mud material. Within the Borels Channel a number of amalgamation surfaces of various styles can be traced laterally for several tens of metres, suggesting that the channel had a complex filling history.

Although the channel is structurally truncated in its distal persevered section, its form and internal architecture suggest it probably connected to deeper bathymetric levels towards the NE when active, and was therefore likely to have been of greater axial extent than its preserved dimensions. Thus the Champsaur Channel Complex is likely to have once continued towards the NE, connecting to a downstream basin that is not currently recognised or preserved. The interpretation of the channel architecture therefore contributes to an interpretation of the broader setting that would otherwise be elusive.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas