THE ZAMBEZI SEDIMENTARY SYSTEM: A RECORD OF THE VERTICAL MOVEMENTS OF THE MOZAMBICAN MARGIN SINCE CREATCEOUS TIMES
Résumé
The Mozambique margin is an oblique to transform margin which houses one of the largest African
turbiditic. The turbiditic system is related to the Zambezi delta which recorded more than 12 km of sediments
deposits with little destabilizations. It is bounded by two fracture zones: to the West the Mozambique ridge
and to the East the Davie fracture zone which controlled the southward migration of Madagascar during the
early Cretaceous. Onshore the Zambezi catchment drains a large domain from the South African plateau to the
southern part of the East African rift system. Linked to several vertical movements and flexures the Zambezi
catchment evolved since early Cretaceous times. Four main episodes have been identified: 1) Early Cretaceous
– Paleocene, 2) Paleocene – Oligocene, 3) Oligocene – Pliocene, 4) Pliocene – Present times. Our objective is
to realise a whole study (paleogeography, thickness maps, sedimentary volumes and budget) of the Zambezi /
North Limpopo system from the vertical movement recorded onshore to the sedimentary deposits both deltaic
and turbiditic since early Cretaceous times, within a well constrained climatic frame. Our first objective was
to perform a new biochronostratigraphic framework based on nannofossils, foraminifers, pollen and spores on
the cuttings of three industrial wells in order to produce for the Zambezi delta a new strong age model and a
continuous paleoclimatic frame evolution. The second target was to recognize the Zambezi/Limpopo different
steps of growth using a dense seismic data-set (industry data and new academic data). Onshore a landform
study from the highest plateau to the present day pediplain was carried out on the Zimbabwe plateau to the
North Malawi area (Tukuyu) in order to better constrain the relative sea level variations which are a proxy of
the deformation. Six step of the Zambezi system evolution were identified:
• Late Jurassic – Late Cretaceous (Albian): the Zambezi delta is defined by a slight slope with reduced
height clinoforms.
• Late Cretaceous – Cenozoic: after a major transgression occurring during Cenomanian times, the
system Zambezi/Limpopo – Save prograded. The location of two main depocentres traduce two sedimentary
supplies: from the Bushveld and the paleo Zambezi.
• Early Paleocene – Late Eocene: A second main transgression flooded the present day coast allowing
the initiation of a carbonate platform (the Cheringoma limestones).
• Oligocene – Miocene: birth of the present day Zambezi delta, tied with (1) a tilt of the north
Mozambican margin during the Oligocene to the middle Miocene related to the southward migration of the
East African rift system, (2) the progressive Zambezi headward erosion leading to the capture of the Luangwa
river located in the middle Zambezi area.
• Miocene – Pliocene: initiation of the Zambezi channel and an export increase of sedimentary materials
towards the most distal part of the deep sea fan.
• Pliocene – Present day: this period is defined by the major catchment evolution of the Zambezi which
doubled with the Victoria Falls capture.
Acknowledgments: This study was founded by TOTAL and IFREMER in the frame of the research
project PAMELA (Passive Margin Exploration Laboratories).