Konservat-Lagerstätten are seen as snapshots of past biodiversity for a given location and time. Yet, processes leading to the exceptional morphological preservation of fossils in these deposits remain incompletely understood. This results in the deficient assessment of taphonomic biases and limits the robustness/relevance of palaeobiological reconstructions. Here, we report the mineralogical characterization of crustacean fossils preserved within carbonate-rich concretions from the Jurassic Konservat-Lagerstätte of La Voulte-sur-Rhône (Ardèche, France). The combination of SEM-EDS, TEM, synchrotron-based XRF, XRD and XANES allows identifying the mineralogical phases composing these fossils (i.e. fluorapatite, Fe-sulfides (pyrite, pyrrhotite) and Mg-calcite) and the surrounding matrix (i.e. Mg-calcite, clays and detrital silicates). Fluorapatite and pyrite (and pyrrhotite) precipitated during decay under anoxic conditions, replacing delicate organic structures and preserving anatomical details. These mineral structures were subsequently consolidated by a Mg-calcite cement. Of note, histologically similar tissues were replaced by the same mineral phases, confirming that ‘fossilization [in La Voulte] occurred rapidly enough to be influenced by tissue composition’. Altogether, the present study shows that exceptional preservation requires fast biodegradation, thereby confirming recent experimental evidence.
.bcf and .rtb files are proprietary files from Bruker, containing SEM-EDXS hypermaps. These files can be opened either using the Esprit software from Bruker, or the Hyperspy suite developped for Python (free).
The association of .hdr and .xim files are XANES stacks. They can be opened and treated with the aXis2000 software (free), specificallly developed and used at the majority of synchrotron beamlines producing such data. Before viewing the data, the stack needs to be aligned.
Brief descriptions of the files are below, and further details are included in the associated README files. All descriptive information is also available in the FileTypes.txt document.
MNHN.F.A70114_thinsection_FIB
Thin section image and localisation of FIB foil extraction, specimen MNHN.F.A70114
Fig-4-A-D-G
EDXS Hypermap, raw data (Bruker file) of specimen MNHN.F.R06054.03. Fig. 4A, D and G
Fig-4-B-E-G
EDXS Hypermap, raw data (Bruker file) of specimen MNHN.F.R06054.03. Fig. B, E and G.
Fig-4-C-F-G
EDXS Hypermap, raw data (Bruker file) of specimen MNHN.F.A70114 Fig. C, F and G.
Fig-5-A-B_stack_XRF_slider
Fig. 5 A-B Synchrotron X-ray fluorescence major-to-trace elemental mapping collected at the DiffAbs beamline, SOLEIL synchrotron. Acquisition parameters: 18 keV excitation energy; 75×75 µm2 scan step; 108,889 pixels; 150 ms counting time per pixel. Specimen MNHN.F.A66910.
For further information, see README_for_Fig-5-A-B_stack_XRF_slider.txt
Fig-5-C-D_stack_XRF_slider
Fig. 5 C-D Synchrotron X-ray fluorescence major-to-trace elemental mapping collected at the DiffAbs beamline, SOLEIL synchrotron. Acquisition parameters: 18.2 keV excitation energy; 50×50 µm2 scan step; 356,942 pixels; 31.5 ms counting time per pixel. Specimen MNHN.F.R06054.03.
For further information, see README_for_Fig-5-C-D_stack_XRF_slider.txt
Fig-6-B-C_stack_XRD_slider
Synchrotron X-ray diffraction mapping collected at the DiffAbs beamline, SOLEIL synchrotron. Acquisition parameters: 18 keV excitation energy; 75×75 µm2 scan step; 108,889 pixels; 180 ms counting time per pixel. Specimen MNHN.F.A66910.
For further information, see README_for_Fig-6-B-C_stack_XRD_slider.txt
Fig-6-D_stack_XRD_slider
Fig. 6 D Synchrotron X-ray diffraction mapping collected at the DiffAbs beamline, SOLEIL synchrotron. Acquisition parameters: 18.2 keV excitation energy; 50×50 µm2 scan step; 356,942 pixels; 22.5 ms counting time per pixel. MNHN.F.R06054.03.
For further information, see README_for_Fig-6-D_stack_XRD_slider.txt
Fig-6-A-diff1_TwoTh_SUM
Sum diffractogram (from XRD mapping data acquired on the HERMES beamline, SOLEIL synchrotron) presented in Fig. 6A, MNHN.F.R06054.03 section. Raw data. 2theta values at the synchrotron energy.
Fig-6-A-diff1_TwoTh_SUM_despiked
Sum diffractogram (from XRD mapping data acquired on the HERMES beamline, SOLEIL synchrotron) presented in Fig. 6A, MNHN.F.R06054.03 section. Treated – artifacts removed. 2theta values at the synchrotron energy.
Fig-6-A-diff2_TwoTh_SUM
Sum diffractogram (from XRD mapping data acquired on the HERMES beamline, SOLEIL synchrotron) presented in Fig. 6A, MNHN.F.A66910 section. Treated – artifacts removed. 2theta values at the synchrotron energy.
Fig-7-A
Raw Ca-XANES (STXM stack) data figured in Fig. 7A. Can be opened with the aXis2000 software.
