Luminescence geochronology (TL/OSL)

Optically (OSL) or thermally (TL) stimulated luminescence dating is based on the emission of light (luminescence) in connection with the recombination of electrons from lattice defects (traps) back to their stable energy state (valence band). The accumulation of electrons in crystalline defects is a function of burial time (non-exposure to light) and the radioactivity of the environment (annual radioactive dose rate). In nature, resetting the luminescence chronometer can be linked to various geomorphological and/or geological processes involving light, heat or friction. Luminescence dating can be applied to address geological-geomorphological problems occurring during the recent Quaternary, typically on timescales of 1 to 100-200 ka (or even more). The targeted minerals are typically quartz and feldspars, and applications range from tracing sedimentary sources, to sediment burial, rock surface exposure and thermochronometry/paleothermometry.

At ISTerre, a luminescence laboratory has been operational since 2023, focusing on dating sediment burial (alluvial, eolian, fluvio-glacial and lacustrine) and rock surface exposure. Sample preparation takes place in a dedicated room under subdued light conditions, where rocks are sawn and sediments sieved before separation by heavy liquids and chemical treatments.

Luminescence measurements are carried out in a second room equipped with an OSL/TL reader (Risø Model DA-20) with a sealed beta radioactive source and a stimulation/detection system adapted to quartz and feldspar minerals. Annual radioactive dose is measured by high-resolution gamma spectrometry in collaboration with the PANOPLY platform (Dr. Olivier Evrard, LSCE Saclay).