Hematite concretions from the Late Jurassic Jhuran sandstone, Kutch, western India: Implications for sedimentary diagenesis and origin of “blueberries” on Mars

Abstract

The discovery of iron-bearing concretions is one of the most exciting discoveries in the recent past on Mars. We report here an analog terrestrial site hosting hematite-bearing concretions belonging to Jhuran sandstone, Kutch, India. Based on petrography, mineralogy, geochemistry and spectral studies (Visible Near Infrared: VNIR and Mössbauer), we show very good similarity between the Jhuran concretions and the “Martian blueberries”. The Jhuran and Martian concretions share similar textural attributes and are of comparable size, but are geochemically different. Based on VNIR study, the mineralogy of the concretions is constrained to comprise hematite, goethite and kaolinite; however, Mössbauer spectra could not detect the pure hematite phase, and instead, suggest the presence of a poorly crystalline mixture of goetheite and hematite. Thus, the Jhuran concretions are most commonly mixtures of goethite and hematite, and not pure hematite. The enrichment of Ni within concretions as compared to the host sandstones is also comparable with the reported Ni-enrichment of Martian concretions. We propose sedimentary diagenesis as the most feasible process that can explain incorporation of Ni into the concretions by coupled substitution in the iron oxide structure. This is inconsistent with the cosmic spherule hypothesis to explain Martian concretion formation, and instead, sedimentary diagenetic processes appear more likely.Finally, the morphology, texture, geochemistry and spectroscopic investigations suggest that the Jhuran iron concretions most likely formed due to sedimentary diagenetic processes, similar to inferences from other Martian analogue localities. Therefore, this study has relevance for understanding the formation processes of Martian blueberries and diagenetic processes on Mars. The Kutch area also has geological similarity with other aspects of ancient Mars and could be a potential testing site for carrying out future Mars exploration studies on Earth.