Fig. 4: Micro-dissolution seams in Sample B.

a XFM map for a macroscopically stylolite-free wackestone sample of the Kaiwhata limestone displaying Ca (grey scale) and Fe (red scale). Sedimentary bedding is vertical. On the right side of the large fossil in the central top of the image, an array of micro-dissolution seams is visible, similarly marked by Ca depletion and Fe enrichment. The blue dash-dot line shows the averaged seam orientation wrapping around and merging with the bedding orientation below the micro-fossil. The white rectangle marks an area, for which averaged Ca and Fe concentrations profiles normal to the dissolution seams have been obtained, shown in (b). The Fe profile in b is shifted downwards by 0.3 units for legibility. Ca is depleted by ca. 40% while Fe is enriched by about 67% in the seams. The inset shows a magnified view of the white box in (a) where arrows mark the positions of micro-dissolutions seams. Fe-rich phases have elongated ellipsoidal or rectangular shapes aligned with bedding. c Reflected-light micrograph of the studied wackestone sample. The white arrow serves as spatial reference to the corresponding three-element XFM map in (d). Dissolution seams appear as very faint schlieren in (c) but are clearly visible in the micro-chemical map (d). Grey colours mark Ca concentrations, red colours correspond to Fe concentrations, and green colours denote Ti concentrations. Ca is depleted in seams (dark-grey colours) while Fe and Ti are enriched. The white rectangle marks an area containing a prominent micro-dissolution seam, for which XFM maps and nano-scale ptychography have been acquired (Fig. 5). The yellow arrows in (d) mark two prominent platy Ti- and Fe-rich minerals, which are not visible at the sample surface in (c). This observation highlights the important volumetric sampling capacity of XFM. The XFM maps used to make this figure are provided in Supplementary Data 2 and 3.