BACKGROUND: SULFATE MINERALS OF THE ALUNITE-JAROSITE GROUP HAVE BEEN IDENTIFIED AT NUMEROUS LOCATIONS ACROSS MARS INCLUDING TWO OF THE ROVER LANDING SITES. BECAUSE JAROSITE ONLY PRECIPITATES UNDER ACIDIC AND OXIDIZING CONDITIONS IT IS USEFUL INDICATOR OF CONDITIONS IN AQUEOUS ENVIRONMENTS ON EARLY MARS. JAROSITE IS ALSO THOUGHT TO DECOMPOSE RELATIVELY RAPIDLY WHEN EXPOSED TO CIRCUMNEUTRAL FLUIDS LEADING TO INFERENCES THAT SITES WHERE THIS MINERAL OCCURS ON MARS HAVE BEEN EXPOSED TO FLUIDS FOR ONLY VERY LIMITED AMOUNTS OF TIME FOLLOWING PRECIPITATION. MANY OCCURRENCES OF JAROSITE AND ALUNITE THAT HAVE BEEN IDENTIFIED ON MARS ARE FOUND IN LAYERED DEPOSITS SUGGESTIVE OF SEDIMENTARY ACCUMULATION BUT THE ORIGIN OF JAROSITE AND ALUNITE IN THESE SETTINGS REMAINS UNCERTAIN. ONE POSSIBILITY IS THAT THESE MINERALS ARE DIAGENETIC PRODUCTS FORMED AFTER THE SEDIMENTS WERE EMPLACED BUT THERE HAVE BEEN VERY FEW TERRESTRIAL ANALOG STUDIES OF DIAGENETIC PRECIPITATION OF JAROSITE AND ALUNITE IN SEDIMENTARY SETTINGS TO SERVE AS A POINT OF COMPARISON. THE PRESENCE OF JAROSITE- AND ALUNITEBEARING CEMENTS IN JURASSIC SEDIMENTARY ROCKS OF THE COLORADO PLATEAU PROVIDES AN OPPORTUNITY TO STUDY DIAGENETIC PRECIPITATION OF THESE MINERALS IN A SETTING THAT MAY BE ANALOGOUS TO LAYERED DEPOSITS ON MARS. ACCORDINGLY WE PROPOSE TO INVESTIGATE THE JAROSITE- AND ALUNITE-BEARING CEMENTS IN THESE ROCKS IN ORDER TO UNDERSTAND THE PROCESSES UNDER WHICH THEY PRECIPITATED AND TO USE THIS INFORMATION TO GAIN INSIGHTS INTO POSSIBLE PATHWAYS FOR THE PRECIPITATION OF ALUNITE-JAROSITE GROUP MINERALS IN MARTIAN LAYERED DEPOSITS. IN ADDITION SINCE THE JAROSITE AND ALUNITE IN THE JURASSIC SANDSTONES/SILTSTONES HAVE PERSISTED FOR FAR LONGER THAN THE INFERRED LIFETIME OF JAROSITE IN AQUEOUS ENVIRONMENTS ON MARS THE PROJECT IS EXPECTED TO PROVIDE NEW INSIGHTS INTO THE POTENTIAL FOR LONG-TERM PRESERVATION OF THESE MINERALS IN MARTIAN DEPOSITS. OBJECTIVES: THE PRIMARY OBJECTIVES OF THE PROPOSED PROJECT ARE TO: (A) DETERMINE THE ORIGIN OF THE JAROSITE- AND ALUNITE-BEARING CEMENTS THAT OCCUR IN JURASSIC SANDSTONES AT MOLLIES NIPPLE UTAH (MN) AND OTHER SIMILAR DEPOSITS ON THE COLORADO PLATEAU AND (B) TO COMPARE THE DEPOSITIONAL ENVIRONMENT AND INFERRED PROCESS FOR PRECIPITATION OF THE CEMENTS WITH LOCATIONS WHERE JAROSITE AND ALUNITE HAVE BEEN IDENTIFIED IN LAYERED DEPOSITS ON MARS TO EVALUATE WHETHER THOSE MINERALS COULD HAVE A SIMILAR ORIGIN. METHODS: THE MINERALOGY CHEMISTRY AND DEPOSITIONAL SETTING OF THE JAROSITE- AND ALUNITE-BEARING SANDSTONES WILL BE THOROUGHLY CHARACTERIZED USING A VARIETY OF APPROACHES INCLUDING FIELD STUDY OF SEDIMENTOLOGICAL STRUCTURES AND ANALYSIS OF ROCKS BY OPTICAL AND SCANNING ELECTRON MICROSCOPY X-RAY DIFFRACTION ELECTRON MICROPROBE ANALYSIS AND VISIBLE/NEAR-INFRARED SPECTROSCOPY. THIS INFORMATION WILL BE USED TO EVALUATE POTENTIAL SCENARIOS FOR PRECIPITATION OF THE JAROSITE/ALUNITE CEMENTS WHICH WILL BE FURTHER TESTED WITH QUANTITATIVE GEOCHEMICAL MODELS. RELEVANCE TO NASA: THE PROPOSED RESEARCH ADDRESSES THE SOLAR SYSTEM WORKINGS OBJECTIVE OF UNDERSTANDING THE EVOLUTION AND MODIFICATION OF PLANETARY SURFACES. IN PARTICULAR THE PROJECT WOULD PROMOTE A BETTER UNDERSTANDING OF THE AQUEOUS PROCESSES AND GEOCHEMICAL CONDITIONS THAT LEAD TO THE WIDESPREAD OCCURRENCE OF SULFATE DEPOSITS ON THE SURFACE OF MARS