Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping

Paleontologists have always tested, used and developed cutting edge imaging techniques to produce the most complete and accurate descriptions of their fossils. Nowadays, efforts are largely driven by taphonomic studies, especially those investigating the exceptional preservation of organic molecules or soft tissues, leading to a series of developments towards molecular and elemental imaging. Paradoxically, although fossils are mostly mineralized materials only the latter is commonly used to infer their mineral composition, but X-ray diffraction, which specifically provides phase identification, received little attention. Here, we show the use of synchrotron radiation to generate, synchronously to X-ray fluorescence major-to-trace elemental maps, megapixel mineralogical maps in transmission geometry using a two-dimensional area detector placed behind the fossil. This approach was applied to millimeter-thick cross-sections prepared through three-dimensionally preserved fossils, as well as to flat fossils. It allows for mineral phases identification (benefitting from the elemental information collected synchronously) and localization at the microscale over centimetric lateral size objects, and further gives information on texture (preferential orientation), crystallites size and local strain, showing great potential for taphonomic studies, as well as other poorly understood (bio)mineralization processes in environmental sciences. We also illustrate that mineralogical contrasts between fossil tissues and/or the encasing sedimentary matrix can be used to visualize hidden anatomies in fossils.