Groupe Latérite: a cross-functional team

(Geochemistry: C. Gautheron, S. Guédron, B. Wild, D. Daval, A. Fernandez-Martinez ; G. Sarret ; TRB: P. Valla, S. Zerathe, Mineralogy: S. Schwartz and E. Janots)

The Laterite group is made up of researchers from a variety of backgrounds (geochemistry, geology, mineralogy, geochronology, geomicrobiology, etc.) from ISTerre and other French institutions. The group focuses its research efforts on understanding the bio-geochemical processes and paleoclimatic cycles that led to the formation of lateritic covers (laterites and ferralitic soils). Understanding the history of their development enables us to identify the mechanisms of enrichment in trace elements (e.g., contaminants, noble and strategic metals...), and their role and sensitivity as the main substrate for biodiversity in the tropical belt. Ultimately, this knowledge is used to develop conservation strategies in conjunction with local stakeholders and scientific partners. This multidisciplinary research is being carried out in two main areas: Amazonia (Brazil, French Guiana and Suriname) and West Africa (Burkina Faso and Guinea).

Related projects:

ECLAT project

(ANR, 2024-2027, correspondents C. Gautheron and S. Guédron)
The ECLAT project brings together universities in French Guiana and mainland France to document the biogeochemical cycles of trace metals and metalloids (TMs; e.g., Hg, Pb, As), and provide societal and public health responses to the problem of TM exposure in French Guiana. The project aims to understand the processes of accumulation, transfer and fate of MTs from lateritic blankets to Guyana’s major rivers (Maroni and Mana). The study of socio-environmental and economic dynamics (gold panning, land use, etc.) will enable us to reconstruct the spatiotemporal evolution of TM flows and anthropic pressure over the last two centuries. At the same time, mineralogical, geochemical and geochronological studies of lateritic blankets will enable us to characterize the processes and dynamics of geogenic and anthropogenic MT accumulation on timescales ranging from centuries to millions of years. Finally, the reactivity of mineral and/or organic MT carrier phases will be studied to document the pathway and fate of these contaminants.

ODyssée project

(CTG Guyane, 2024-2027, correspondent S. Guédron)
Mining in French Guiana remains an important economic activity, but one that is not without consequences for the environment and health. Rehabilitating mining sites after exploitation is proving to be the best alternative for limiting impacts, enabling a return to soil equilibrium after exploitation. The ODyssée project "Origine et Dynamique des contaminants (mercure et autres métaux et métalloïdes) au cours de la Réhabilitation et refonctionnalisation des sols de sites miniers en Guyane Française" brings together researchers from ISTerre, CNRS, BRGM and the University of Guyana to study the speciation and biogeochemical dynamics of mercury (Hg) in association with the study of the ecological refunctionalization of soils. It aims to (i) evaluate, using an isotopic approach, the accumulation of mercury in the various compartments (soil/plant/atmosphere) in order to identify the sources and carrier phases during the mining and rehabilitation of mining sites, and (ii) assess the functional state of rehabilitated soils and the link between this state and the sequestration of mercury and other metal or metalloid contaminants (Pb, As, Cd).

WISE project

(BQR ISTerre, 2023-2024, correspondent B. Wild)
This interdisciplinary project brings together new southern partners (Univ. A. de Kom, Suriname/Guyane region) and several areas of ISTerre expertise (geochronology, mineralogy, geomorphology, microbiology and experimental geochemistry) around the problem of white sands in the intertropical zone. In addition to their geological interest as markers of paleo-environmental conditions, these formations are the focal point of emblematic ecological and societal issues in the South. This project will provide new quantitative constraints on (1) the genesis of these formations, (2) the chronology of their development, (3) the maintenance of associated ecological niches, and (4) their potential for valorization, particularly in the context of sustainable fertilization of agrosystems. This project proposes a new approach to complex ecological and geological structures, combining environmental DNA, dating (luminescence, cosmogenic nuclides), mineralogical and geochemical characterization, and in situ experimentation (mineral incubations). It will draw on the expertise of local partners (Univ. Guyane and Univ. A. de Kom) and will be accompanied by a mutual transfer of knowledge with ISTerre teams.

Rehab project

(Labex OSUG and DGTM Guyane, 2022-2025, corresponding S. Guédron)
The ReHab project studies the hydro-biogeochemical dynamics of metallic contaminants (Pb, Hg, Cd) and metalloids (As) in association with the study of the ecological functionalization of soils to be able to provide integrative answers, methodological tools, for a sustainable rehabilitation of gold mining sites in French Guiana. This project is based on Naomi Nitschke’s CIFRE thesis (ANRT-Gaïa SAS). The study is based on a mining flat in French Guiana, with different stages of operation (opening, closure, rehabilitation carried out at different times). It is approached in a comparative manner (different stages of rehabilitation/revegetation), multi-scale spatially [from ecosystem compartments (pore space, soil, rhizosphere, biomass and atmosphere) to the plot] and temporally (from the flood event to the multi-year scale) using transdisciplinary tools [analytical chemistry (elemental, speciation and spectroscopy), erosion and sediment transport physics, functional ecology, and microbiology].

MynAFaso project

(BQR ISTerre and IRD, 2022-2025, corresponding S. Guédron)
The MynAFaso project studies the impact of gold panning in Burkina Faso and Guinea on contamination and human exposure (epidemiology) to cyanide and metallic (Pb, Hg, Cd) and metalloid (As) contaminants. This project is centered on the thesis of Djamilatou Dabre (ACE Partners). Firstly, the project aims to map the levels and speciation of Hg, As and other associated contaminants (Se, Pb, Cd...) in the environment (soil, sediment, macrophytes...) and to (ii) assess their fate (mobility, carrier phases) in hydrosystems. The second part of the research focuses on assessing the levels of impregnation of aquatic species (MeHg) and the levels of exposure of populations (Hg and As) and the associated health risks. Finally, the identification of aquatic plant species (macrophytes) and biofilms capable of sequestering these contaminants in aquatic ecosystems will enable the development of pilot systems for water remediation/mitigation (such as filter gardens) and/or phytostabilization of contaminants in contaminated soils affected by gold-mining activities.

Laterite project

(BQR ISTerre, 2021-2022, corresponding C. Gautheron)
This "Laterite" project was part of a transverse initiative between three teams and is based on the study of the formation and evolution of the critical zone (s.s. soils, laterites). These soils are essential components of the critical zone on which we live and extract georesources. However, major questions remain as to the climatic conditions enabling their development, and the paleoclimatic events that favored their formation, as well as the temporal and genetic relationships between laterite and soil. To answer these questions, we have launched a pilot project in French Guiana, with the aim of transferring it to Brazil as well, combining geochronological (OSL, 14C, cosmogenic isotope 10Be, (U-Th)/He) and geochemical (major, trace, organic matter, d13C, REE) methods. This project has enabled us to strengthen our existing collaborations with our partners in French Guiana (University, BRGM, mining companies), and to launch the first OSL and cosmogenic isotope geochronology data via the supervision of an M2 student.

RECA project

(ANR, 2020-2023, corresponding C. Gautheron)
This ANR RECA project aims to quantify the impact of climate change on laterite formation and its evolution over time. To answer these questions, we combined for the first time different methods from geochronology, mineralogy and geochemistry. Only by combining these methods was it possible to unravel the information, characterizing alteration regimes and conditions over time. This project, focusing on laterites developed since the Cenozoic on the rocks of the Guiana craton, set out to date the different generations of supergene minerals using two complementary methods, and to identify the major alteration phases, in order to link them to major climatic changes. Mineralogical and geochemical studies enable us to reconstruct paleoenvironmental conditions and quantify the intensity of weathering. These results enable us to identify major weathering phases over the Cenozoic, with different environmental conditions (water quantity, temperature, duration of processes) for each phase. In addition, deciphering the conditions of laterite formation and evolution helps us to understand landscape evolution, and to link their evolution with changes in biodiversity.