Stratigraphy of an Interbasinal Deep-Water Conduit: Lessons Learned from the Grand Coyer Sub-Basin, Eocene-Oligocene Grès d’Annot Sandstone, SE France

Renaud Bouroullec¹, Mark Tomasso¹, David, R. Pyles², and Keumsuk Lee¹. (1) Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713-8924, phone: 512-471-4971, Renaud.Bouroullec@beg.utexas.edu, (2) Department of Geology and Geological Engineering Colorado School of Mines, Colorado School of Mines, Golden, CO 80401

Salt withdrawal mini basins contain significant petroleum reservoirs in the deep northern Gulf of Mexico. These minibasins are physically connected by large canyon-like features that serve as conduits for sediment gravity flows bypassing from proximal basins into adjacent distal basins. The Grand Coyer exposure of the Eocene-Oligocene Grès d'Annot Formation of the French Alps provides an excellent outcrop analog of an interbasinal conduit that connects the proximal southern Annot sub-basin to the distal northern Trois Evéchês sub-basin. Stratigraphic columns, paleocurrent, photomosaic and lidar data were collected to address the stratigraphy of the conduit.

Stratigraphic data in the Grand Coyer area reveal that the paleo-conduit was 5-6 km wide, 10-12 km long and 450 m thick at its axis. The conduit was laterally and longitudinally asymmetric, narrowing and steepening toward the distal sub-basin. The external shape of the conduit is inherently related to the stratigraphic architecture and net-to-gross distribution. The conduit early fill is composed of MTCs and very coarse-grained channelized strata, while the later fill is showing a fining upward trend and a decrease in local confinement. The proximal part of the conduit axis contains laterally offset, or stacked, non-amalgamated channels, while the distal part of the conduit shows amalgamated, vertically stacked channels. Strata in axial positions of the conduit contain upwards of ~80% sandstone, regardless of position in a proximal to distal transect through the conduit. The lateral margins of the conduit contain strata with ~30% sandstone, and show a mixed association of lobe-shaped finer-grained strata, slumps and growth faults. The lessons learned from Grand Coyer paleo-conduit could be used to better predict sand distribution and reservoir geometry within interbasinal conduit.

Effects of Active Structural Growth and Confined Basins on Sandbody Architecture (SEPM/AAPG)
2007 AAPG Annual Convention and Exhibition (April 1 - 4, 2007) Technical Program