THE ZAMBEZI SEDIMENTARY SYSTEM:A SOURCE TO SINK APPROACH

The Mozambique margin is an oblique to transform margin which houses one of the largest African turbiditic system (1800 km long and 400km wide) (Droz and Mougenot., AAPG Bull., 1987). The turbiditic system is related to the Zambezi delta which recorded more than 12km of sediments deposits with little destabilizations. In the onshore area, the water catchment and the drainage system have been changed through geological times by rivers captures (Thomas and Shaw., J.Afr.Earth Sci., 1988). Since a few years several studies were realised along the central African margins which led to numerous interpretations, especially on timing of events liked to the lack of a strong age model. The aim of this study is to carry out a source to sink approach along the Mozambique margin and to discuss its evolution since Early Cretaceous times. Within the framework of the Pamela project, a new set of acquisition cruise and data analysis was realised. A biostratigraphy revaluation of wells along the Mozambique shelf combined to a resampling and new datation of Zambezi 3 well provided new ages constraints that we correlated to existing and new Pamela seismic reflexion data. Using this new data set we propose to: 1) realise a new age model of the Mozambican margin since early Cretaceous times, 2) analyse the infill evolution from the Zambezi delta to the deep turbiditic system using isopach maps to recognize its different steps of growth. 1) Late Jurassic (?) - early Late Cretaceous: from Neocomian to Aptian times, the high of the clinoforms is getting higher, with the first occurrence of contouritic ridges during Cenomanian times. 2) Late Cretaceous - Early Paleocene: a major drop of relative sea-level occurred as a consequence of the South African Plateau uplift. The occurrence of two depocenters suggests siliciclastic supplies from the Bushveld and from the North Mozambique domain. 3) Early Paleocene - Eocene: growth of carbonate platforms and large contouritic ridges. 4) Oligocene - Present-day: birth of the modern Zambezi Delta, with quite low siliciclastic supply during Oligocene times, increasing during Miocene times linked to the East African system. As previously expected (Droz and Mougenot) some sediments are coming from a feeder located east of the Davie Ridge. This study was financed by TOTAL and Ifremer in the scientific project PAMELA (Passive Margin Exploration Laboratories) framework