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The Rio Tinto Basin, Spain: Mineralogy, Sedimentary Geobiology, and Implications for Interpretation of Outcrop Rocks at Meridiani Planum, MarsExploration by the NASA rover Opportunity has revealed sulfate- and hematite-rich sedimentary rocks exposed in craters and other surface features of Meridiani Planum, Mars. Modern, Holocene, and Plio-Pleistocene deposits of the Rio Tinto, southwestern Spain, provide at least a partial environmental analog to Meridiani Planum rocks, facilitating our understanding of Meridiani mineral precipitation and diagenesis, while informing considerations of martian astrobiology. Oxidation, thought to be biologically mediated, of pyritic ore bodies by groundwaters in the source area of the Rio Tinto generates headwaters enriched in sulfuric acid and ferric iron. Seasonal evaporation of river water drives precipitation of hydronium jarosite and schwertmannite, while (Mg,Al,Fe(sup 3+))-copiapite, coquimbite, gypsum, and other sulfate minerals precipitate nearby as efflorescences where locally variable source waters are brought to the surface by capillary action. During the wet season, hydrolysis of sulfate salts results in the precipitation of nanophase goethite. Holocene and Plio-Pleistocene terraces show increasing goethite crystallinity and then replacement of goethite with hematite through time. Hematite in Meridiani spherules also formed during diagenesis, although whether these replaced precursor goethite or precipitated directly from groundwaters is not known. The retention of jarosite and other soluble sulfate salts suggests that water limited the diagenesis of Meridiani rocks. Diverse prokaryotic and eukaryotic microorganisms inhabit acidic and seasonally dry Rio Tinto environments. Organic matter does not persist in Rio Tinto sediments, but biosignatures imparted to sedimentary rocks as macroscopic textures of coated microbial streamers, surface blisters formed by biogenic gas, and microfossils preserved as casts and molds in iron oxides help to shape strategies for astrobiological investigation of Meridiani outcrops.
Document ID
20080026258
Acquisition Source
Johnson Space Center
Document Type
Reprint (Version printed in journal)
Authors
Fernandez-Remolar, David C.
(Instituto Nacional de Tecnica Aeroespacial Torrejon de Ardoz, Spain)
Morris, Richard V.
(NASA Johnson Space Center Houston, TX, United States)
Gruener, John E.
(NASA Johnson Space Center Houston, TX, United States)
Amils, Ricardo
(Instituto Nacional de Tecnica Aeroespacial Torrejon de Ardoz, Spain)
Knoll, Andrew H.
(Harvard Univ. Cambridge, MA, United States)
Date Acquired
August 24, 2013
Publication Date
November 30, 2005
Publication Information
Publication: Earth and Planetary Science Letters
Publisher: Elsevier B.V
Volume: 240
Issue: 1
ISSN: 0012-821X
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other

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