Head of Research at the CNRS. UMR 8212 CNRS-CEA-UVSQ Laboratory of Climate and Environmental Science.
Studying speleothems (stalagmites, stalagmitic floors) to recreate palaeoenvironments and date specific elements (scree at the entrance, collapses, etc.).
Speleothems are used to recreate the climate of the past. The stable isotopes in calcite, those in surrounding liquids, chemical elements, the surrounding organic material, the evolution of dead C and the speed of growth are among the signs used to recreate palaeoenvironments. Certain speleothems possess seasonal growth layers (visible, UV and geochemical), meaning that annual climate change can be seen. Calcite isotopes (d13C et d18O) recorded global climate events such as g/ig transitions and millennary events (Dansgaard-Oeschger, Youger-Dryas, Bølling-Allerød). These markers, together with uranium-thorium (U/Th) dating applied to calcite (up to 500 ka), provide us with records of the evolution of the climate in the interior of the continents, with an unequalled absolute chronology, at least for periods before 40 ka, and would appear to be complementary to other registers (ice, oceanic sediment, lakesides, trees, coral etc). We are currently developing the quantitative aspect of the climactic signs by recreating the temperature of formation based on 47 measurements of the isotopes in liquid incursions on modern natural and artificial deposits (experimenting with calcite precipitation under controlled conditions).
The dating carried out on the stalagmites and stalagmitic floors in Chauvet cave have enabled us to lay significant chronological foundations in order to know more about their geomorphological history: the minimum age of the scree at the entrance, the collapse of the Hillaire Chamber and the archaeological floors. At the same time, the analysis of stable isotopes carried out on the stalagmites enabled us to recreate the evolution of ancient climate in different periods, before, during and after human occupation. The most remarkable result is without doubt the recreation of the palaeoclimatic variability in the last deglaciation with a resolution and relevance comparable to glaciary and lakeside registers. In order to better interpret the geochemical signs from speleothems, hydrological and isotopic surveillance of infiltration water was set up; this completes the modern climactic studies carried out by F. Bourges.