Abstract:

Sea-floor bathymetry is one of the principal controls on the routing of turbidity currents and the subsequent distribution of deposited sediments. Re-created sea-floor bathymetry is thus one of the main inputs for process-based numerical simulation of ancient turbidite systems. The sea floor underlying the Early Oligocene deposits of the Peïra Cava basin (Alpine foreland, southern France) has been re-created from an outcrop dataset by subjecting a surface-based 3D model to stepwise backstripping of overburden and removal of the post-depositional structural overprint. The surfaces that make up the 3D model were constructed based on field data including stratigraphic correlations, structural measurements and geological maps. Since deposition the Peïra Cava turbidites have been folded, faulted, tilted, uplifted and partly eroded, all of which was summarized and then accounted for during re-creation of the palaeo-sea floor. Uncertainties associated with the input parameters used for the re-creation include the lithological composition of the overburden and underburden, palaeo-water depth and structural restoration. The impact of these uncertainties was addressed by creating a range of scenarios within viable ranges for each of the separate parameters and then comparing the relief and geometry of re-created surfaces. Two mid-case palaeobathymetric surfaces were selected and used as input for process-based simulation of turbidity currents using commercially available software designed for modelling density flows. The simulation results were compared with the stratigraphic architecture observed at outcrop. The quality of the correlation was used as a test of how well the re-created palaeobathymetry mimics the true ancient sea floor.

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