Figure 4

Scanning electron microscopy (SEM) (a–c) and polarized light microscopy (PLM) (d–f) images for the samples K1B (a,d), K2B (b,e) and K3B (c,f). The limestone grain K1B shows a clear porous structure (see panel a), while the other grains do not show a significant porosity in the SEM images (see panel b and c). The bright spots observed especially in K2B correspond to surface charging of isolated regions within the grain. The PLM images show that all grains are made of pure calcite while K3 also contains some quartz particles. K1 contains a lot of fossil fragments (panel d) embedded in a microcrystalline (micritic) carbonate matrix. K2 (panel e) is a fine crystalline to micritic limestone with round elements (spherulites). In K3 (panel f), single areas of fine crystalline calcite are found in an otherwise majorly micritic matrix. More SEM and PLM images can be found in Figs S1 and S2 of the supplementary information.