An improved method for reconstructing the stratigraphy and bathymetry of Continental margins: Application to the cenozoic tectonic and sedimentary history of the Congo margin

A number of techniques, such as backstripping and forward modeling, have be en previously used to reconstruct the tectonic, sedimentary, and thermal hi story at passive margins. Still, these techniques are generally inaccurate in places such as the west African margin where the stratigraphic record is disrupted by continuous faulting of the sediment pile caused by salt tecto nics and by erosional unconformities. The ability to reconstruct the strati graphy, salt thickness, and water depth along profiles of these types of ma rgins is important for determining the factors controlling the geological h istory of the margin and the evolution of hydrocarbon systems. To reconstruct the stratigraphy, paleowater depths, and salt flowage on a p rofile across the Congo margin, we combined backstripping and palinspastic reconstruction. This enabled us to restore the faulting and salt flowage an d simultaneously to take into account the isostatic response of the lithosp here to sediment loading and unloading. This method allowed us to estimate the paleowater depth, as well as the stratigraphy, and the geometry of the sedimentary section on the profile through time. The determination of the r egional isostatic response of the lithosphere is performed with the use of a new model to estimate the flexural rigidity of continental lithosphere. T o demonstrate this method, we perform the Cenozoic reconstruction of the Co ngo margin. The results yield a coherent geological history of the margin from the Eoce ne to the present. In the Eocene the margin was a carbonate ramp With a dee p-seated shelf break (600 m). During the Eocene-Oligocene transition, inter mediate water-depth oceanic currents triggered submarine erosion of the Eoc ene slope and shelf. From the Miocene to the present, we observe a large in crease in the input of terrigenous elastic sediments. As a result, the shel f prograded 40 km across the Eocene ramp. As the elastic sediments prograde d across the margin into the deep basin, faulting of the sediment pile and salt withdrawal caused the formation of grabens in places where salt swells had previously formed. Finally the reconstruction suggests that the Congo margin was uplifted by at least 330 m between the late Oligocene and the mi ddle Miocene.