Malawi P

Approximately 70% of Earth’s emerged relief is characterized by erosional low-gradient reliefs also known as planation surfaces (PS). Geomorphologists defended the idea that some of them, and particularly the higher ones, may correspond to relics of old uplifted reliefs, preserved from total erosion, and with ages about tens of millions of years.
For instance, according to the work of King (1962), South America and Africa shared potential relics from the Gondwana and Post-Gondwana paleosurfaces. These surfaces have been correlated with high plateaus, mainly present in the southern and eastern part of this continent, with an altitude about 2000 to 3000 m a.s.l.
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The age and evolution of the lower surfaces of this continent, the so called African (End of Cretaceous to mid-Eocene) and post African planation surfaces (Mid-Tertiary to the end of Tertiary), begin to be more constraints with the help of the dating of the tropical regoliths developing at their expanse. These data also pointed to the fact that they mainly evolved due to stepwise dissection, a phenomenon that promotes the formation of glacis and pediments typical of the African landscapes. A contrario, the age of exposure of the African high plateaus (2000/ 3000 m a.s.l), their chronology of uplift, weathering and erosion are currently poorly known. These knowledges are however critical to confirm their link with the Gondwana and Post-Gondwana surfaces, and therefore their existence.

Objectives

The main objectives of the project in Malawi are to cross tropical regolith dating and geomorphological studies in order to understand the evolution of the Southeast African landscape. It is focused on the study of the Malawi area, a region hosting several relics of paleosurfaces identified by geomorphologists. This project aims to study the lateritic profiles developed over several surfaces in Malawi by dating the clays and iron oxides and characterizing the mineralogy and geochemistry of the profiles
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In order to answer these questions, a regolith sampling mission was organized in partnership with the Malawian Geological Survey, the University of Rennes 1 and Total. All the methodologies and approaches of the RECA project will be used on the sampled East African laterite and duricrust samples.

This project will throw another light on the geological history of the Southern African landscape, either by revealing the age of exposure of the high planation’s surfaces from this region and by analyzing the main periods of formation and evolution its tropical regoliths. It will also provide clues to understand the factors that can promote the preservation of old high reliefs through the geological times, a phenomenon also observed on other continents such as South America or Asia. Moreover, this project will also open doors to futures studies that will explore the age of exhumation of high plateaus from other countries of Southern Africa.
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