Cordilleran Section - 113th Annual Meeting - 2017

Paper No. 12-4
Presentation Time: 8:30 AM-5:00 PM


RAMPE, Elizabeth B.1, MING, Douglas W.1, GROTZINGER, John P.2, BRISTOW, Thomas F.3, BLAKE, David F.3, VANIMAN, David T.4, CHIPERA, Steve5, GELLERT, Ralf6, MORRIS, Richard V.7 and MORRISON, Shaunna M.8, (1)NASA Johnson Space Center, Astromaterials Research and Exploration Science Division, 2101 Nasa Pkwy, Houston, TX 77058, (2)California Institute of Technology, Pasadena, CA 91125, (3)Exobiology, NASA Ames Research Center, MS 239, Moffett Field, CA 945035, (4)Planetary Science Institute, Tucson, AZ 85719, (5)Chesapeake Energy, Oklahoma City, OK 73154, (6)Department of Physics, University of Guelph, Guelph, ON N1G 2W1, Canada, (7)NASA Johnson Space Center, Houston, TX 77058, (8)Geophysical Laboratory, Carnegie Institution, Washington, DC 20015,

The Mars Science Laboratory Curiosity rover landed in Gale crater in August 2012 to investigate the strata of lower Aeolis Mons (i.e., Mount Sharp) and characterize their depositional and diagenetic environments. Visible/short-wave infrared spectra from orbit of these strata show variations in phyllosilicate, sulfate, and Fe-oxide minerals, suggesting these units record environmental changes that occurred during the early Hesperian. Curiosity has traversed over 15 km and has climbed through ~200 m of stratigraphic section, made up of predominantly fluviolacustrine (i.e., the Bradbury group and the Murray formation) and aeolian (i.e., the Stimson formation) units. Multiple geochemical and mineralogical instruments are onboard Curiosity to study these ancient rocks, including the Chemistry and Mineralogy (CheMin) instrument, which is an X-ray diffractometer (XRD) and X-ray fluorescence spectrometer, and the Alpha Particle X-ray Spectrometer (APXS).

Geochemical and mineralogical variability in the Murray formation point toward changes in depositional and diagenetic environments and sediment sources over time. The base of the Murray formation, represented by the Pahrump Hills and Marias Pass localities, was deposited in a lacustrine environment and displays incredible mineralogical and geochemical variability over ~15 m of section. CheMin data show a change from samples with abundant pyroxene, phyllosilicate, and hematite with minor jarosite at the base of the Pahrump Hills to a sample in Marias Pass that lacks these minerals and instead is dominated by feldspar and amorphous and crystalline SiO2 with minor magnetite and Ca-sulfate. This variability may represent a change in the sediment source region, in addition to a change in depositional and/or diagenetic environment. The most recent CheMin measurements of the Murray formation show remarkable consistency in mineralogy over ~50 m of section. These samples contain abundant phyllosilicate, hematite, Ca-sulfate, and feldspar, with minor pyroxene. The observation of significant Ca-sulfate is consistent with geomorphological and geochemical evidence for desiccation of the lake environment in this interval. Furthermore, the abundance of hematite suggests the fluids at the time of deposition and/or diagenesis were oxidizing.