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Original Article |
1 1Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK Present address: Institute of Petroleum Engineering, Heriot-Watt University, Riccarton Campus, Edinburgh EH14 4AS, UK (e-mail: lawrence.amy@pet.hw.ac.uk)
2 2Earth and Biosphere Institute, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
3 3Department of Geology and Petroleum Geology, College of Physical Sciences, Meston Building, King's College, Aberdeen AB24 3UE, UK
Basins in which turbidity currents are completely or partially trapped are common in many tectonically active, deep-water settings. Field study of an Eocene–Oligocene turbiditic system in the Peïra Cava area, a sub-basin of the Alpine foreland in southeastern France, allows spatial characterization of a ponded basin fill on the basis of a correlation framework derived from measured outcrop sections and photomosaics. The basin-fill architecture comprises a sand-rich, proximal scour-and-fill facies and a downstream transition to mud-rich, basin-plain turbidite sheet facies. The proximal facies is interpreted to have formed directly downstream of a slope break, where currents were highly erosional during some periods and highly depositional during other periods, as a result of the interacting effects of turbulence enhancement and rapid deceleration. Both the proximal facies and the downstream transition to distal basin-plain facies occur in progressively landward positions at higher stratigraphic levels. The landward shift in depositional facies is likely to have resulted from the basin-floor aggradation and a landward migration of the slope break. This ‘back-stepping’ process may be expected to occur in many ponded turbiditic basins and to produce a similar type of sedimentary architecture.
