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Published December 19, 2008 | Supplemental Material
Journal Article Open

Orbital Identification of Carbonate-Bearing Rocks on Mars


Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.

Additional Information

© 2008 American Association for the Advancement of Science. Received for publication 18 August 2008. Accepted for publication 3 November 2008. We thank R. Arvidson, R. Morris, N. Mangold, A. Baldridge, J.-P. Bibring, D. Jouglet, A. Fraeman, S. Wiseman, A. McEwen, G. Marzo, P. McGuire, and M. Wyatt for thoughtful discussions during manuscript preparation and E. Cloutis and others who have made quality spectral libraries available and contributed to the building of the NASA/Keck Reflectance Experiment Laboratory (RELAB) spectral database. We are grateful for the ongoing efforts of the MRO science and engineering teams, in particular the CRISM team, which enable these discoveries.

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