EVIDENCE FOR MICROBIALLY INFLUENCED PRESERVATION IN THE OLIGOCENE AIX-EN-PROVENCE KONSERVAT-LAGERSTÄTTE, FRANCE

The Aix-en-Provence Konservat-Lagerstätte of France is an Oligocene lacustrine deposit with an abundance of fossil insects and spiders preserved as compressions and high-relief internal and external molds in laminated marlstone. Previous researchers have suggested calcite replacement, compressions, and microbialites as possible mechanisms for preservation, but the taphonomic pathway of this Fossil-Lagerstätte has not yet been systematically examined, especially with regard to the controls on diagenesis and fossilization of the terrestrial arthropod assemblage.

We investigated the texture and geochemistry of the Aix-en-Provence fossils and their matrix with three different types of microscopy: petrographic, epifluorescence and scanning electron, as well as elemental characterization. All techniques showed evidence suggestive of microbial activity. Petrographic microscopy of the matrix reveals three distinct fabrics: finely laminated, filamentous, and granular, all with morphology reminiscent of microbially induced sedimentary structures. Both fossil and matrix material are strongly autofluorescent, suggesting the presence of organic material. Scanning electron microscopy revealed diatoms and spherules coated in filamentous bacteria, conclusions supported by elemental distributions. Together, these techniques provide extensive evidence for microbial mats and other microbiological activity, which we hypothesize played a role in this exceptional fossilization. These results of our investigations suggest a complex taphonomic pathway, in which microbial mats and microorganisms likely played a major role in the preservation of fossils from the Aix-en-Provence Fossil-Lagerstätte. The evidence presented here is consistent with the textural and chemical signatures of microbially driven fossil preservation in other Konservat-Lagerstätte from lacustrine deposits.