Fig. 5: Nano-scale chemical and structural maps of an individual micro-dissolution seam.

a XFM Ca map of a micro-dissolution seam from Sample B and its immediate surroundings. Seam boundaries obtained with automated segmentation (see the “Methods” section) are marked with white lines. The maps in (b)–(f) have the same scale. b Fe map, c Ti map, d Si map, and e Compton scattering map for the same area shown in (a). Fe, Ti, and Si are enriched within the seam. The XFM map of Compton scattering intensity (arbitrary units) demonstrates higher intensity within seams, indicating a density increase. f Nano-scale ptychographic map of the phase (in radians) of the complex X-ray wavefield exiting the sample. The micro-dissolution seam does not display a marked structural difference in comparison to the micritic matrix. g Polar plot of the relative long-axis orientation-frequency distribution of Fe- and Ti-rich phases mapped in (b) and (c). Long-axis orientation was determined from best-fit ellipses to Fe particles with concentrations ≥50 μg/cm² and Ti particles with concentrations ≥of 15 μg/cm². To minimise discretization errors, phases made of <30 pixel and with aspect ratios <2 were disregarded. Most phases are aligned with bedding (vertical red line) within ±5°. h Histograms of the relative concentration frequency distributions of Fe and Si as well as Compton-scattering intensity, respectively, demonstrate that dissolution seams exhibit elevated magnitude of these quantities. The XFM maps and ptychogram used to make this figure are provided in Supplementary Data 4.