Jxa 8200 superprobe

Mineral chemistry of silicate minerals was determined by WDS using a JEOL JXA 8200 superprobe at the Institute of Geological Sciences of the University of Bern, operating with an acceleration voltage of 15 keV, a probe current of 10 nA, and a beam diameter of 1 μm. Spot analyses were measured for each mineral phase present. The mass fractions of 8 element oxides were calibrated using synthetic and natural standards. High-resolution maps were acquired using the wavelength dispersive spectrometers (WDS) and point analyses serving as internal standards (Lanari and Piccoli 2020 ). Analytical conditions included acceleration voltage of 15 keV and probe current of 100 nA to compensate for the short dwell times (Lanari and Piccoli 2020 ). X-ray maps were corrected for dead time, classified, and standardized using XMapTools 4 (Lanari et al. 2014 , 2019 ). Different measurement settings and standards were employed for silicate, oxide, and sulfide minerals, which is described in detail in Supplementary Information S1.

EMP was employed to analyse the chemical composition (major, minor and some trace elements) of the glass in exposed MIs and their host clinopyroxene crystals. The analyses were conducted at the C.N.R., Institute of Geosciences and Georesources in Padova, using a Cameca SX50 EMP (samples AL14, AN18, NEW31, and NS12), and at the Department of Earth Sciences, University of Milano, using a JEOL JXA 8200 Superprobe (samples AN137A, NS9, and NS12). As indicated by replicate analyses of standards and unknown samples at both laboratories, the analyses conducted at Padova and Milano are equivalent and comparable, for the level of accuracy required in the present study (Supplementary Tables 2 and 6). Natural and synthetic standards were used for instrumental calibration. For the measurement of the glass in exposed MIs, a 1 μm beam diameter was used to avoid contamination from the surrounding host minerals. Standard beam current and accelerating voltage conditions were applied (Supplementary Tables 2 and 6).

EMP analysis was performed with a JEOL JXA 8200 Superprobe. Carbon-coated polished sections of rostrum and human tooth enamel (outermost region) were studied with an accelerating voltage of 15 kV. Quantitative point analysis was accomplished with a beam current of 25 nA and a beam diameter of 20 μm. The elements F, Na, Mg, P, S, Cl, K, and Ca were selected for quantitative analysis by wavelength-dispersive X-ray spectroscopy (WDS). The calibration standards for the EMP analyses included natural geological minerals: Durango apatite (Ca₁₀(PO₄)₆F₂) for Ca, P, and F, albite (NaAlSi₃O₈) for Na, synthetic forsterite (Mg₂SiO₄) for Mg, anhydrite (CaSO₄) for S, microcline (KAlSi₃O₈) for K, and tugtupite (Na₄AlBeSi₄O₁₂Cl) for Cl. The spot analyses were randomly distributed throughout the transverse sections of enamel and rostrum.

A JEOL JXA-8200 Superprobe equipped with five wavelength dispersive crystal spectrometers (WDS) and one energy dispersive spectrometer (EDS) housed at the Institute of Geological Sciences, University of Bern was used for quantitative spot analyses and X-ray mapping. A backscatter detector (BSE) was used for imaging and micro-textural analyses. Samples were measured with 15 kV acceleration voltage and 20 nA probe current. Measurement time included 20 s on the peak and 10 s on background positions on either side of the peak. Natural and synthetic oxide and silicate minerals were used as standards. X-ray maps were acquired using a pixel size of 2 µm, a dwell time of 200 ms and a probe current of 100 nA. Spot analyses used as standards for the map quantification were acquired prior to mapping with the WDS spectrometers. Maps were processed, calibrated and analysed using the software XMapTools (Lanari et al. 2014 (link), 2019 (link)).

In order to obtain a better understanding of the internal architecture of the trace fossils, three samples were cross-sectioned through a vertical mid-plane passing from the upper to lower surface using a lapidary saw with no water. One side was cross-sectioned through the equator, perpendicular to the first cut. All cut surfaces were polished for higher-resolution observation. Scanning electron microscopy (SEM) was used to image the internal structure of the trace fossils and micro-CT analysis was unsuccessfully employed to observe internal architecture of one of the trace fossils due to a lack of density differences between the different materials. One of the cross-sectioned para-types was also vacuum impregnated with epoxy and polished to observe internal structures in better detail and to construct a microprobe mount. Element concentrations were measured using EDS and BSE images of the sample were taken to examine preservation patterns of the nests and fungus combs (Figs 2 and 4). This work was conducted on an electron probe microanalyser (EPMA; Jeol JXA8200 “superprobe”) at the Advanced Analytical Centre (AAC) at James Cook University.