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Instability: Processes and Products |
UMR 5125 CNRS, Paléoenvironnements et Paléobiosphère, UFR Sciences de la Terre, Université Claude Bernard, Lyon 1, 69622 Villeurbanne cedex, France savary{at}univ-lyonl.fr
The Barremian-Aptian Baronnies syncline, located in SE France, provides the opportunity to study a calcareous turbidite lobe with intercalated breccias and slumps. These features are formed in-situ by the emplacement of turbidity currents that distorted the underlying semi-consolidated substrate. The brecciation occurs in three stages. The first stage is represented by the penetration of calcarenitic sediment into the underlying unlithified calcisiltic sediment due to the hydraulic pressure of an overriding turbidity current. In the next stage, a pseudo-breccia forms where the brecciated clasts are still attached to the substrate. Finally, these breccia clasts are separated entirely from the seabed and locally entrained into the flow. In addition, the penetration of the flow into the underlying semi-consolidated sediment can induce destabilization, down slope movement and folding. Similar Tithonian-aged (Late Jurassic) breccias have been interpreted previously as in-situ wave-induced features in this region; however, this study testifies that this deformation is not diagnostic of storms but can also be induced by turbidity current deposition.
The mechanisms that induce brecciation have to be identified correctly in order to consider them within a sequence stratigraphic context. Calcareous turbidites and their associated breccias, however, are not strongly diagnostic of relative sea-level.
