Multi-scale basin dynamic study of the Danakil Depression (Afar)

Rime, Valentin

doi:10.51363/unifr.sth.2025.060

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Doctoral thesis

Multi-scale basin dynamic study of the Danakil Depression (Afar)

DOKPE

Rime, Valentin University of Fribourg
Foubert, Anneleen (Degree supervisor) ORCID University of Fribourg

2023 ; Fribourg (Suisse) : Département de géosciences, sciences de la terre, Université de Fribourg

1 ressource en ligne (290 pages) ; 1 fichier pdf

PhD: Université de Fribourg (Suisse), 2023

English Rifts and passive margins are fundamental features of the structure of Planet Earth. They mark the transition from continents to oceans and, as such, are an essential component of plate tectonics. However, the interactions between tectonics, sedimentology and magmatism controlling rift structure and evolution are poorly known due to the complexity of the factors playing at very different temporal and spatial scales. Because they are the locus of large sediment accumulations, rift basin form detailed archives to reconstruct paleoenvironmental and paleoclimatic conditions and host important natural resources.
The Danakil Depression is part of the Afro-Arabian Rift System and is the only emerged region on Earth currently experiencing the transition from continental rifting to oceanic spreading. As such, it provides a unique natural laboratory to study rifting processes. Despite its indisputable interest, scientific knowledge of this region remains fragmented due to challenging field access. The aim of the present work is to better understand the basin dynamics of the Danakil Depression using a multiscale and multi-disciplinary approach.
An integrative review of the tectonic, magmatic and sedimentological history of the Afar region and the compilation of new geological maps allows to develop a new model for the evolution of the Afar Depression. This results in the better understanding of the regional rift system kinematics. In particular, results highlight that rifting is propagating northward in Afar. Results also evidence that the Danakil Depression and Central Afar have a different structure and contrasting geological evolution. They represent two different rift types and nottwo different stages of evolution of the same type of rift. Differences can be explained by the influence of the Afar hotspot.
The gradual and active transition from continent to ocean is also reflected in the Pleistocene to Holocene environmental conditions of the Danakil Depression. Field studies evidence at least four times flooding of the basin by the Red Sea during the Quaternary. Field data complemented by remote sensing allow to characterize the parameters controlling the marine incursions in the basin. Tectonic uplift of the rift shoulder modulates the height of the gateway between the Red Sea and the Danakil Depression and forms the long-term, firstorder control. The short-term, secondorder control is eustatic sea-level variations. The tectonic uplift explains why the basin was not flooded during the Holocene. Tentative predictions on the future flooding of the Danakil Depression are discussed.
The last marine incursion occurred ~130 ky ago, resulting in the deposition of several hundred of meters of evaporites during its desiccation stage. The study of a 625 m deep core drilled in the central part of the Danakil Depression allows to characterize the paleoenvironmental and paleoclimatic conditions of the Depression since the Late Pleistocene. This study furthermore identifies the mechanisms of evaporite formation, providing important clues on the understanding of older enigmatic salt giant deposits in Earth history.
Finally, the hypersaline Lake Afdera is a peculiar Recent sedimentary setting in the Danakil Depression. The origin of the Lake is discussed based on bathymetric mapping. Bathymetry shows that the deepest part of the Lake represents the lowest known elevation of the Danakil Depression. This is explained by the interaction of faults of different orientations representing the intersection of the rift axis with two transfer zones.
Overall, the present study allows the better understanding of the evolution, the chronology, the structure and the paleoenvironmental and paleoclimatic conditions of the Danakil and Afar Depression, as well as some of the mechanisms controlling these dynamic and complex systems. This regional study gives new insights on the understanding of rifting processes shaping our Planet since more than two billion of years. The results of this thesis will also have an impact on the exploration, management and exploitation of natural resources in this region, such as groundwater but also geothermal energy, salt, potash, and other mineral resources. Finally, results may contribute to highlight and protect the unique and fascinating geology of the Danakil Depression.

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