a1 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
a2 Géosciences Rennes, UMR 6118, CS 74205, 35042 Rennes Cedex, France
a3 CNRS UMR 5202, Muséum National d'Histoire Naturelle, Entomologie, CP 50, F-75005 Paris, France
a4 Museum für Naturkunde der Humboldt–Universität zu Berlin, D-10115 Berlin, Germany
a5 LGBPH Poitiers, UMR 6046, F-86022 POITIERS Cedex, France
A significant portion of Mesozoic amber is fully opaque. Biological inclusions in such amber are invisible even after polishing, leading to potential bias in paleoecological and phylogenetic studies. Until now, studies using conventional X-ray microtomography focused on translucent or semi-opaque amber. In these cases, organisms of interest were visualized prior to X-ray analyses. It was recently demonstrated that propagation phase contrast X-ray synchrotron imaging techniques are powerful tools to access invisible inclusions in fully opaque amber. Here we describe an optimized synchrotron microradiographic protocol that allowed us to investigate efficiently and rapidly large amounts of opaque amber pieces from Charentes (southwestern France). Amber pieces were imaged with microradiography after immersion in water, which optimizes the visibility of inclusions. Determination is not accurate enough to allow precise phylogenetic studies, but provides preliminary data on biodiversity and ecotypes distribution; phase contrast microtomography remains necessary for precise determination. Because the organisms are generally much smaller than the amber pieces, we optimized local microtomography by using a continuous acquisition mode (sample moving during projection integration). As tomographic investigation of all inclusions is not practical, we suggest the use of a synchrotron for a microradiographic survey of opaque amber, coupled with microtomographic investigations of the most valuable organisms.
(Received October 09 2007)
(Accepted October 24 2007)