Slope Canyon-Channel Systems, Offshore Northern Tanzania, Record the Tectonic History of Pemba and Zanzibar Islands

Abstract

Summary The Tanzania margin is dissected by Pemba and Zanzibar islands, unusual structures for a passive margin and which origin is still a matter of debated. In this study, using 2D seismic reflection profiles and five exploration wells, we generate “pseudo-3D” reconstructions of the slope canyon-channel pathways from the Oligocene to Recent. We observe a decrease in slope canyon-channels during the middle-upper Miocene which is interpreted to reflect the onset of the uplift of Pemba Island. The extensional tectonic regime, established since lower Miocene and still ongoing, led the seafloor deformation and reduced sediment supply downslope, progressively disconnecting turbidite channels from their feeding systems. Slope channels offshore Zanzibar were still active at that time, thus indicating that the uplift of this island occurred later, starting from the upper Miocene-lower Pliocene. Changes in seafloor topography also promoted the formation of two newly discovered giant canyons that represent the main sediments conduits for this sector of the western Indian Ocean since the Miocene. Supported by these results, we proposed a conceptual model for the post-Oligocene stratigraphic evolution of the northern Tanzania margin that contemplates a potential relationship between the islands and the East African Rift System.