Partenaires

CNRS
Ministère de la Culture et de la Communication
Université Versailles Saint-Quentin


Rechercher


Accueil > News

Direct measurement of the oxidation state of cerium at microscale across fossils

publié le

P. Gueriau, C. Mocuta, and L. Bertrand. Cerium anomaly at microscale in fossils. Analytical Chemistry, 87(17):8827–8836, 2015 [article]

Concentrations of rare earth elements in sediments and fossils, in particular cerium that, as an exception, adopts both the +III and +IV oxidation states depending on redox conditions, lie at the heart of many studies aiming at assessing past environments chemistry. New analytical developments, carried out in the frame of long-term collaboration between IPANEMA, the French National Museum of Natural History and the DIFFABS and LUCIA beamlines of SOLEIL, allowed a direct micrometric mapping of the oxidation state of cerium in well-preserved 95-million-year-old fossils.

The new approach set up by IPANEMA is based on the collection of X-ray absorption spectra and on the production of speciation maps through the collection of successive micro-X-ray fluorescence maps at excitation energies across the Ce L3-edge. It reveals a remarkably homogeneous oxidation state of cerium, partly under the +IV form, within and between different fossil fishes and shrimps from the locality. The presence of cerium under the +IV form suggests slightly oxidative local conditions of burial, and agrees well with the indirect data obtained from the usual point concentrations.

This study provides a complementary approach to better describe and constrain palaeo-environmental indicators up to now essentially studied using invasive and destructive laboratory techniques without imaging capacities, and shows a high potential in other rare earths fields such as the mining industry, metallurgy, or medicine.

Voir en ligne : Article on Analytical Chemistry website


+