¹Sayantan Guha,¹Shiba Shankar Acharya,²Mruganka Kumar Panigrahi
Journal of Geophysical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2025JE009601]
¹Department of Geology, Presidency University, Kolkata, India
²Department of Geology and Geophysics, Indian Instituteof Technology, Kharagpur, India
Published by arrangement with John Wiley & Sons

The western Kutch basin, India, provides a unique window into aqueous alteration under extreme acid-sulfate conditions. While previous research focused primarily on the Matanomadh Formation, this study presents a systematic investigation of hydroxy-sulfate minerals-including jarosite, alunite, minamiite, gypsum-across several chronostratigraphic units, spanning the pre-Deccan Ghuneri Member (Late Cretaceous) through post-Deccan formations (Matanomadh, Naredi, Harudi). Using a comprehensive analytical suite (XRD, XRF, FTIR, Raman, SEM-EDS, δ34S) and laboratory-synthesized potassium jarosite dissolution experiments, this work provides a complete solution to the source, formation, and preservation of these minerals. Isotopic data identify the primary source of iron and sulfur as the oxidation of precursor pyrite by meteoric water. A significant finding is the documentation of a natural natrojarosite–natroalunite solid solution, where Al-substitution enhances structural stability, making Na-jarosite more abundant than K-jarosite. Notably, field associations and geochemical data indicate that host-rock composition exerts only a minor influence on the formation of these jarosites. Crucially, our data reveal that the formation of these hydroxy-sulfate phases cannot be attributed to a single geological event or a specific past timeframe. Instead, we demonstrate that these minerals are geologically recent and continue to form as an ongoing process under current environmental conditions. The long-term preservation of these assemblages is primarily governed by the region’s prevailing aridity and localized mineral buffering associated with their mode of occurrence along the fractures of host rock. The discovery of the natrojarosite–natroalunite solid solution provides key insights into acid-sulfate system evolution on both Earth and Mars.