Environmental archives

(S. Guédron, A. Gourlan, C. Gautheron)

The geochemistry team tackles the reconstruction of paleoclimates, paleohydrology, paleoecology and human footprints (e.g. geoarchaeology and mining paleo-pollution) from environmental archives (lake, peat and marine sediments, lateritic profiles) on different time scales (from century to hundred of million years).

These approaches are carried out using various proxies such as biotic tracers (e.g. pollens, diatoms...) and geochemical; elemental and isotopic (e.g. δ18O, δ13C, δPb, δNd, δHg...). The team is also developing "unconventional" tracers to refine the tracing of atmospheric sources (e.g Br and Se) or redox paleoenvironments (δFe, δNd, δHf...). In addition, the team is developing geochronological approaches to date certain archives (e.g. laterite profiles, ferruginous crust...) over million of years timescales using (U-Th)/He dating methods (see Laterite Group: a cross-disciplinary team).

INSU Project EC2CO 2021-22

Correspondent A. Gourlan
Lead exposure in Roman and medieval mining populations: multi-isotopic tracing (5Pb and Cu) of human exposure from bones and natural archives.

RECA project

(ANR, 2020-2023, correspondent C. Gautheron)
This ANR RECA project aims to quantify the impact of climate change on the formation of laterites and their evolution through 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.