Effects of Syn-Depositional Deformation from the Stratigraphic Architecture of from Interbasinal Deep-Water Conduit, Grand Coyer Sub-Basin, Eocene-Oligocene GrèS D’Annot Formation, SE France

Renaud Bouroullec¹, Mark Tomasso², and David R. Pyles^1
1Chevron Center of Research Excellence, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO
²Enhanced Oil Recovery Institute, University of Wyoming, Laramie, WY

Slope minibasins are often physically connected by large interbasinal conduits. Those features serve as transfer and storage zones for sediment gravity flows bypassing from proximal basins to adjacent distal basins. Subsurface data do not allow for detailed characterization of the syn-depositional structuring of reservoirs within those features. An outcrop analog was studied to illustrate the impact of syn-depositional structuring on the stratigraphic record of an interbasinal conduit.

The Grand Coyer exposure of the Eocene-Oligocene Grès d’Annot Formation of the French Alps provides an excellent example of a large deep-water interbasinal conduit that connects the proximal Annot sub-basin to the distal Trois Evéchês sub-basin. Stratigraphic columns, paleocurrent, photomosaic and lidar data were acquired to address the tectono-stratigraphic evolution of the conduit. Stratigraphic data reveal that the conduit was 6 km wide, 10-12 km long and 400 m deep at its axis. It was laterally and longitudinally asymmetric, and narrowing and steepening distally. The conduit early fill shows a predominance of large syn-depositional slides at the axis and along the lateral margins of the conduit. Those slides have different geometry and directions of movements related to the initial topography of the conduit. A deep Alpine growth structure, located underneath the central part of the conduit, is interpreted as having triggered an oversteepening, generating upward mud remobilizations due to local gravitational gliding. Other syn-depositional structures, active in the later conduit-fill stages, comprise sandstone bed imbrications along the conduit margins and large growth faults in the distal part of the conduit. The lessons learned from Grand Coyer paleo-conduit could be used to better predict reservoir geometry, compartmentalization and connectivity within interbasinal conduits.

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