Quantification and causes of the terrigeneous sediment budget at the scale of a continental margin: a new method applied to the Namibia–South Africa margin

Abstract

International audienceThe terrigeneous sediment budget of passive margin basins records variations in continental relief triggered by either deformation or climate. Consequently, it becomes a major challenge to determine sediment accumulation histories in a large number of basins found in various geodynamic contexts. In this study, we developed a GIS-based method to determine the sediment budget at the scale of a whole basin (from the upstream continental onlap to the most distal deepest marine deposits) and the associated uncertainties. The volume of sediments preserved in the basin for each time interval was estimated by interpolation between cross-sections and then corrected from in situ production and porosity to obtain terrigeneous solid volumes. This approach was validated by applying it to Namibia-South African passive margin basins for which independent data are available. We determined by a statistical approach the variances associated with each parameter of the method: the geometrical extrapolation of the section (8-43%), the uncertainties on seismic velocities for the depth conversion (2-10%), on the absolute ages of stratigraphic horizons (0.2-12%), on the carbonate content (0.2-46%) and on remaining porosities estimation (3-5%). Our estimates of the accumulated volumes were validated by comparison with previous estimates at a lower temporal resolution in the same area. We discussed variations in accumulation rates observed in terms of relief variations triggered by climate and/or deformation. The high accumulation rates determined for the Lower Cretaceous, progressively decreasing to a minimum in the Mid-Cretaceous, are consistent with the progressive relaxation of a rift-related relief. The following increase to an Upper Cretaceous maximum is consistent with a major relief reorganization driven either by an uplift and/or a change to more humid climate conditions. The lower accumulation rate in the Cenozoic suggests a relief reorganization of lesser amplitude over that period

Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction

“…The plume influence is also suggested by erosion and uplift of the Southern African Plateau in the Late Cretaceous (Fig. 2, label 16; MacGregor 2010; Guillocheau et al 2012;Colli et al 2014). Similar uplift and erosion is also recorded in West Africa (Leprêtre et al 2014).…”

“…15: India-Asia convergence (van Hinsbergen et al 2011). Label 16: Sediments accumulation rates on South African margins (Guillocheau et al 2012). The peak centered on 80 Ma comes after a period of increasing sediment discharge and a period of uplift and erosion of South Africa.…”

Key Future Directions For Research On Turbidity Currents and Their Deposits

“…This question links to allied work on other sediment transport systems in the earth-surface-processes community. Further studies may focus on Quaternary systems or other locations where key external controls are independently well constrained and source-to-sink sediment budgets can be reconstructed (Clift et al 2001;Guillocheau et al 2012;Petter et al 2013). This topic is important for understanding the climatic record in submarine fan sequences as well as how these systems are perturbed by humans.…”

Topographic growth around the Orange River valley, southern Africa: A Cenozoic record of crustal deformation and climatic change

“…The measurement of silicilastic sedimentary fluxes along the Atlantic passive margin (Guillocheau et al, 2012) indicates an amount of silicilastic sediments of around 2 millions of km 3 , most of it sourced by onshore denudation. As previously argued by Burke and Gunnell (2008), this means that the first late Cretaceous plateau was removed by denudation and that the present-day relief is…”