--> Abstract: Flow Processes in Slope-Confined Turbidity Currents: Evidence from the Annot Sandstone, Late Eocene, SE France, by Marco Patacci, William M. McCaffrey, and Peter Haughton; #90078 (2008)

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Flow Processes in Slope-Confined Turbidity Currents: Evidence from the Annot Sandstone, Late Eocene, SE France

Marco Patacci1, William M. McCaffrey2, and Peter Haughton1
1School of Geological Sciences, University College Dublin, Dublin, Ireland
2Institute of Geological Sciences, The University of Leeds, Leeds, United Kingdom

The late Eocene Crête de la Barre Section near the village of Braux in SE France is a well-known and intensively studied example of a turbidite system onlapping a slope. Tabular laterally continuous beds and high-quality exposures allow single beds to be traced from the basin floor to where they pinch-out. A re-investigation of the onlap has established that a range of flow types impinged on the slope - conventional high and low concentration turbidity currents and hybrid flows depositing linked turbidite-debrite couplets. The purpose of this study is to document how flow style determines facies transitions and onlap style at bed scale. Debrites sandwiched within turbidites at onlap sites have been interpreted as the result of local slope failures triggered by incident turbidity currents. However, the debrites could also have been sourced up-dip by flow partitioning. A key issue is to be able to differentiate downlapping (distal) terminations from onlapping (lateral) terminations.

Low-density turbidites next to the onlap are characterized by thin repetitions of massive sand and ripple laminations resulting in a distinctive banded appearance. They gradually thin toward the slope, mantling the paleotopography. High-density turbidites are usually thicker and characterized by poorly or ungraded sandstone. These beds are tabular and infill the topography, pinching-out over very short distances at the base of the slope. Turbidite-debrite couplets consist of massive sandstone overlaid by a muddy sandstone with abundant carbonaceous material. Both bed components pinch-out against the slope together. However, when turbiditic sand on the top of the debrite is present, it drapes further upslope.

 

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