Description du sujet de thèse

The Guiana Plateau, located in the northern part of Amazonia near the equator, is a vast territory covering some 2.5 million km2, and is today hosting a vast taxonomic diversity in both terrestrial and aquatic ecosystems. However, little is known about the past biodiversity of this region, particularly in French Guiana, even for relatively recent periods such as the Upper Pleistocene and Holocene. This lack of knowledge also concerns the reconstruction of paleo-environments in French Guiana, and of the geomorphological dynamics, which are still poorly understood and whose timing is highly speculative. Yet this information is needed to trace the chronology and modalities of changes in palo-biodiversity, as well as in human dispersal and settlement during the Pleistocene-Holocene in the Guianas, in relation to existing palaeo-landscapes and palaeo-environmental conditions.
The objectives of the PhD project are to reconstruct the paleo-landscapes and geomorphological context underlying ecosystem evolution in northern French Guiana during the Late Pleistocene (125-12 ka) and Early Holocene (12-8 ka). The project is organized around two complementary axes: (1) Pleistocene coastal dynamics (mainly in regions of Matiti and Coswine) : reconstructing the evolution of coastal features during the Pleistocene, in relation to sea-level oscillations and the influence of the Amazon sediment plume. This approach involves reconstructing the spatial distribution of coastal deposits along the coastal plain of French Guiana, studying their sedimentology and provenance, and dating their deposition. This axis will also be coupled with a quantification of coastal rock erosion, and an exploration of the possible record of marine biodiversity (environmental DNA) in sedimentary archives.
(2) Geomorphological evolution of the Maroni River and its tributaries: quantifying fluvial dynamics and alluvial sediment production in French Guiana during the Pleistocene. Alluvial archives along major rivers, such as the Maroni which has already been partly mapped, and its tributaries, bear witness to a long-term geomorphological evolution whose modalities, drivers and timing are not known. Three key questions structure this axis: (1) the origin and distribution of perched alluvial plateaus, sometimes located several tens of meters above the present-day network; (2) the processes responsible for the organization of fluvial terraces along the Maroni; and (3) the stratigraphic and possibly co-genetic links between alluvial deposits and weathered bedrock.
The doctoral project will provide a geomorphological and chronological framework for the reconstruction of paleoenvironmental conditions in northern French Guiana. The study of littoral sites will allow to infer the position of the shoreline through time and possible sediment source variations. Associating littoral deposits with past altitudes and distance to the Atlantic Ocean will constitute a major asset in the interpretation of paleobiodiversity and ecosystem results from the PHENOMENA ANR project. The project will also provide a comprehensive mapping of the alluvial and coastal sedimentary units with their morphological and physico-chemical characteristics, as well as source/chronology differences along northern French Guiana. The study of alluvial sedimentary units and coastal bedrock sites will allow quantifying paleo-erosion rates over the Pleistocene, which are key to reconstruct paleo-landscapes. Finally, the post-depositional evolution of alluvial/coastal sediments will provide a reference framework for the preservation of geochemical, fossil, and genomic information, and a context for human occupation in French Guiana.

Contexte de travail

The Centre national de la recherche scientifique (CNRS) is one of the world's leading research institutions. To meet the major challenges of today and tomorrow, its scientists explore life, matter, the Universe and the workings of human societies. Internationally recognized for the excellence of its scientific work, the CNRS is a benchmark for the world of research and development, as well as for the general public
ISTerre is a joint research unit of Grenoble Alpes University, CNRS, USMB, IRD and Gustave Eiffel University, located at 1381 rue de la Piscine 38400 Saint-Martin d'Hères on the Bourget du Lac Science Campus. It employs around 300 people and has an average annual budget of €7 million. ISTerre is part of the Observatoire des Sciences de l'Univers de Grenoble (OSUG), and carries out multidisciplinary research in Earth Sciences, focusing on approaches combining natural observations, experimental research and modeling of the Earth system. Grenoble is a pleasant city surrounded by the Alps, with access to a wide range of sports and outdoor activities, and a high quality student life.
The doctoral project is part of a project funded by the Agence Nationale de la Recherche (ANR) entitled PHENOMENA: “Pleistocene and HolocENe ecOsysteMs and palEobiodiversity of FreNch GuianA” (scientific leader: P.-O. Antoine, ISEM Montpellier). In addition to the doctoral contract, the PHENOMENA project will cover financial requirements for field missions, analyses and planned travel (collaborations and conferences) as part of the project. In addition, the PhD student will be a full member of the PHENOMENA team, with effective participation in conferences and meetings associated with the project.

Skills :
The candidate should have knowledge in at least one of the following fields of Geosciences: quantitative geomorphology, Quaternary geology, geochronology, sedimentology and/or sedimentary geochemistry.
Skills in topographic analysis and GIS mapping, as well as a strong interest in team fieldwork and laboratory work, are required to successfully complete the project and develop the planned collaborations.
Candidates should have a Master's degree in Geology, Geophysics, Physical Geography or another quantitative natural science discipline, with a strong interest in land surface dynamics.
Candidates must have proven oral/written communication skills in English (at least partial mastery of French will be an advantage, particularly for social interactions and life in Grenoble, as well as during field missions in French Guiana).

Benefits :
- annual vacation entitlement: 45 working days
- inter-company restaurant
- reimbursement of public transport costs (75%)
- mutual participation
- telecommuting
- cultural and sporting activities
- sports facilities

Contraintes et risques

/

Informations complémentaires

/