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Jarosite in Gale Crater, Mars: The Importance of Temporal and Spatial Variability and Implications for HabitiabilityThe Curiosity rover has recently found evidence for small amounts of jarosite, a ferric sulfate, in the Pahrump Hills region at the base of Aeolis Mons (Mount Sharp), Gale crater. While jarosite has been described previously at other locations on Mars, including several sites at Meridiani Planum (explored by the Opportunity rover; and Mawrth Vallis (by remote MRO-CRISM observations; this is the first identification in Gale. Jarosite is interpreted to be a mineral indicator of acidic conditions (pH less than 4; on Earth, it is most commonly found in acid rock-drainage or acid sulfate soil environments. However, jarosite has also been described from a number of terrestrial environments where widespread acidic conditions are not prevalent. As a case study, we describe here an occurrence of sedimentary pyrite nodules that have been variably oxidized in situ to gypsum, schwertmannite, K-/Na-jarosite and iron oxides in a polar desert environment on Devon Island, Nunavut, Canada. Remarkably, these nodules occur in loosely consolidated carbonate sediments, which would have required a higher pH environment at their time of formation and deposition. Thus, acidic conditions may only exist at a small (sub-cm) scale or in a restricted temporal window in an otherwise well-buffered environment. On Devon Island, the jarosite occurs in the most oxidized nodules and is never associated directly with pyrite. Schwertmannite, a metastable iron oxyhydroxysulfate that can form at pH higher than that required for jarosite, occurs in association with partially oxidized pyrite. The paragenetic sequence observed here suggests initial formation of schwertmannite and late-stage precipitation of jarosite in restricted micro-environments, possibly forming via transformation of an amorphous schwertmannite-like phase. While the carbonate environment on Devon Island differs significantly from that of Gale crater, i.e., where we find predominantly basaltic sedimentary rocks, this terrestrial analog provides insight into the significance of jarosite with respect to habitability. For example, the variable abundance of jarosite on Mars and possibly in Gale crater points to potentially localized conditions favorable for jarosite formation. Interestingly, small amounts of sulfide minerals have also been detected by Curiosity at Yellowknife Bay; oxidation of sulfide minerals at Pahrump could explain the presence of small amounts of jarosite. The iron-rich rocks at Pahrump may also represent relatively altered basaltic sediments, or they could be sediments that were altered further by a fluid with a distinct, possibly more acidic, composition. In addition, the abundance of iron-rich amorphous material in Gale rocks allows for the possibility that pre-cursor, iron-bearing phases transform to jarosite post-depositionally. Thus, the occurrence of jarosite at Pahrump could reflect changing paleoenvironmental conditions, though continuing study of its context and textural relationships should provide a fuller understanding of the significance of this mineral to past fluid compositions and past habitability at Gale crater.
Document ID
20150018569
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Leveille, R. J. (McGill Univ. Montreal, Quebec, Canada)
Oehler, D. Z. (Jacobs Technology, Inc. Houston, TX, United States)
Fairen, A. G. (Cornell Univ. Ithaca, NY, United States)
Clark, B. C. (Space Science Inst. Baltimore, MD, United States)
Niles, P. B. (NASA Johnson Space Center Houston, TX, United States)
Blank, J. G. (Wyle Labs., Inc. Moffett Field, CA, United States)
Date Acquired
October 1, 2015
Publication Date
June 15, 2015
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
JSC-CN-33087
Meeting Information
Meeting: Astrobiology Science Conference (AbSciCon2015)
Location: Chicago, IL
Country: United States
Start Date: June 15, 2015
End Date: June 19, 2015
Sponsors: Lunar and Planetary Inst., Universities Space Research Association, Smart Sparrow Pty Ltd., Montana Univ., Tokyo Inst. of Tech., Blue Marble Space, NASA Headquarters
Distribution Limits
Public
Copyright
Public Use Permitted.

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