17 février 2023 - 14h45-15h30

Antoine Vite – Stagiaire en projet long de recherche (École Normale Supérieure de Lyon) au laboratoire IPANEMA
Institut Photonique d’Analyse Non-destructive Européen des Matériaux Anciens (IPANEMA), site du Synchrotron SOLEIL, 91190 Saint-Aubin

Titre : Assessing the chemical modifications associated with the entrapment of insects in amber using infrared spectro-imaging

Résumé : Amber is a unique medium for fossilization in which spectacular anatomical details are regularly retained. However, amber deposits show a broad range of preservation degrees, from a complete absence of inclusions to the preservation of finely detailed cellular features. The preservation is sometimes so impressive that it has long been thought that ancient DNA could be retrieved from organisms entrapped million years ago. In numerous occurrences, the inclusions are in fact only hollow moulds, and the taphonomical processes as well as the conditions that led to such a preservation gradient remain poorly understood. Once an insect is entrapped in resin, it is indeed eventually subjected to dehydration, biological decay, high pressure and temperature. These processes induce structural and/or chemical changes, and coupled with a variety of environmental conditions they result in different fossilization modes, which allow for the preservation of the anatomy and/or the chemical composition of the inclusions.

The aim of my internship is to characterize the chemical changes caused by heating using infrared spectro-imaging with the particular objective to identify and constrain the loss of chemical information associated to two temperature thresholds (around 150 and 200°C) that have been proposed to distinguish between different types of amber. I placed Drosophilia melanogaster individuals in epoxy resin, which is chemically neutral for the organism tissues, and heated a series of these artificial samples up to 250°C. I prepared ultrathin sections (1-2 μm thick) from the maturated samples, characterized them using infrared hyperspectral imaging (Bruker VERTEX 70) and compared the results with several references. The use of infrared spectroscopy enabled me to quickly assess the eventual losses in terms of chemical functional groups. The experiment has been performed twice, using different resin viscosities.

My first results show that infrared spectra are quite stable for a short heating time, with most of the vibrations remaining throughout the experiment. This suggests that chemical transformations appear from a duration superior to 6 hours. I also noticed that viscosity decreases the extent of penetration of resin within the cuticle, and could explain partly the diversity of the preservation gradient observed between amber deposits.

Le séminaire aura lieu sous format hybride. Si vous souhaitez y assister, vous pouvez demander le lien de connexion à l’organisateur : Laurent Tranchant (laurent.tranchant@synchrotron-soleil.fr).