Extended Data Fig. 1: Carbonate size distribution between grain inclusions and loose grains.

Histograms of the distribution of the carbonate ROIs in the analysed samples, by carbonate species, and between carbonates as grain inclusion and as loose grain. Diameters are given for equivalent circular ROIs, but shapes can be very irregular. ‘Inclusions’ are for carbonate ROIs detected within a part of a larger grain, ‘loose grains’ are for grains that appear entirely carbonate-bearing. Extracted grains (mostly > 1 mm in width) are deposited in individual sample holders. Small grains (mostly <100 µm in width) are found with them in the same sample holders, either transported together with the main grain during extraction from the bulks, or detached from the main grain during movements of the sample holder. In the category ‘extracted grains’, the large carbonate inclusions (plain colour) are within the main grains, but small carbonate loose grains (hashed colour) are also detected around. The majority of carbonate inclusions are in the extracted grains, which is expected as only the largest grains were extracted. In the sub-bulks, which mostly contain a finer fraction of the grains, carbonate ROIs correspond mostly to loose carbonate grains.