Abstract The Chemical Index of Alteration (CIA) is the most accepted of available weathering indices. Past conditions of physical and chemical weathering can be reliably inferred if application of the CIA is combined with a comprehensive facies analysis. When applied to the reconstruction of climate conditions during Neoproterozoic times, CIA data provide crucial insights into the changes in the relative contributions of chemical and physical weathering in the production of sedimentary detritus. CIA data are thus instrumental not only in documenting changes between icehouse and greenhouse climates, but also in recognizing shorter-term climate oscillations between glacial and warm–humid conditions. Concerning the Neoproterozoic glacial periods, sedimentological and CIA data sets give strong evidence of a functioning hydrological cycle, operative sediment routing systems, and variable climate conditions oscillating between dry–cool and glacial, and warm–humid and interglacial. These findings are incompatible with the hypothesis of a totally ice-covered Snowball Earth.

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