Chemical Index of Alteration (CIA).
(a) CIA weathering profiles for shale deposits (black rings) and IFs (orange rings). Reference paleosol indices (green rings36. (b) Scaled up paleosol data. (c) Fluctuating CaO concentrations in shales and IFs in panel a. CIA and CaO data are averages for specific formations (comprising a total of more than 800 data points), calculated from values provided in ref. 36 and from major elemental concentrations in references given in supplementary Table 1. Red arrows correspond to icehouse periods. The recorded high CIA indices for recent hydrothermal sediments at Milos correspond to pervasive shallow submarine hydrothermal leaching of seafloor basement rocks, common for the Hellenic volcanic arc, Greece25.