Description du sujet de thèse

The thesis project funded by ANR NILAFAR (https://geoazur.oca.eu/fr/anr-nilafar) aims to:
1. quantify the hydrological variations of the Afar depression from the lakes of the Abhe sedimentary basin to improve our understanding of the mechanisms behind the aridification episodes over the last 20,000 years,
2. study at high-resolution recent hydrological changes and explore the co-evolution Climate-Human-Environment.
This PhD research project is based on the study of cores AFA-18 and GEM-18 from the CLIMAFAR 2018-20 project (leader L. Khalidi CEPAM-CNRS) and the long core ABH23 from the ANR NILAFAR (leader M. Revel, https://geoazur.oca.eu/fr/anr-nilafar).
The sediments of these lakes constitute a unique hydro-climatic record of the past continental environment of the watersheds of these three lakes for the last 20.000 years.
The student will focus on:
● to improve the chrono-stratigraphy of the studied sedimentary sequences (14C dating on bulk material and possibly on specific compounds, radionuclides, paleomagnetism),
● to the analysis of the major element distribution (X-ray Fluorescence Core scanner, DRX) as well as the composition and abundance of organic biomarkers (GDGTs, fat acids, n-alkanes, triterpenes, HBI, MO isotopic - 13C- and molecular  2H,  13C-, MO characterization) of the sedimentary sequences AFA18-02, GEM-18-3/4 and ABH23.

In order to :
● to characterize the nature of organic and inorganic compounds in lake sediments i) on the recent time scale (Afambo short sequence) and comparison with meteorological variables to improve the interpretation of these tracers at the level of the Afar Depression; ii) on the Holocene and deglaciation scales to study fossil biomarkers of the soils of the Afambo, Gamari and Abhe lake catchment and to reconstruct the hydrological variations
● to define the timing and modalities of onset and termination of the arid episodes around 4.2 ka and 8.2 ka. These results will be put in perspective with recent works on the expression of the 4.2 and 8.2 events on the African continent, north of Madagascar, in the Mediterranean and in the Atlantic and Indian Oceans (link with the El Nino process) in order to improve the understanding of the mechanisms controlling the African monsoon.


Requirements to apply:
● Have a master degree in geosciences, paleoclimatology, geology or geochemistry
● Organizational ability and large autonomy
● Ability and curiosity to develop a multi-disciplinary approach and Great communications skills

Contexte de travail

The thesis will be co-supervised by Marie Revel, Guillemette Ménot and Fabien Arnaud. This thesis work, whose financing is acquired, relies on the consortium which carries the ANR NILAFAR research project. The first year of the thesis will be spent at the Geoazur laboratory (including several missions at Edytem co-supervised by Fabien Arnaud) for the sedimentary geochemistry part. The second and third years will be spent at the LGLTPE ENS-Lyon for the analytical organic geochemistry (integrating missions at the LSCE in collaboration with Jérémy Jacob) in order to become familiar with the methods of organic geochemistry as well as the interpretation of geochemical signatures.
This PhD project including numerous national bilateral collaborations:
i) with Jessie Cauliez (TRACES) and Lamya Khalidi (CEPAM), archaeologists, specialists in the Neolithic transition in the Horn of Africa
ii) with Eric Chaumillon (LIENSs) expert in seismic reflection who will bring his insight on the active neotectonics of the Afar region
iii) with Nathalie Vigier (LOV- UMR7093, Villefranche sur Mer) for the erosion and alteration of lake sediments
iv) with Pierre Brigode (Geoazur) for hydrological modelling;
and international collaboration with researchers from the ORREC (Observatoire Régional de la Recherche pour l'Environnement et le Climat) in Djibouti.

The candidate will carry out his activity within the Geoazur laboratory of the University of the Côte d'Azur, CNRS, located in the Sophia-Antipolis technology park. The Géoazur laboratory is a multidisciplinary research unit made up of geophysicists, geologists and astronomers federating around major scientific issues: telluric hazards (seismic, gravity and tsunamigenic) and the associated risks, the dynamics of the lithosphere and the Earth imagery, geodesy-metrology of the Earth and the near Universe. The laboratory is made up of approximately 170 researchers and teacher-researchers and structured into 6 thematic teams.