GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 15-8
Presentation Time: 9:55 AM


TU, Valerie M.1, RAMPE, Elizabeth B.2, BRISTOW, Thomas F.3, BLAKE, David F.3, VANIMAN, D.T.4, MORRIS, R.V.5, MING, Doug6, YEN, Albert S.7, ACHILLES, Cherie N.8, CASTLE, Nicholas9, MORRISON, Shaunna M.10, DOWNS, Robert T.11, HAZEN, Robert M.12, CRAIG, Patricia I.13, DES MARAIS, David J.14, TREIMAN, Allan H.9, CHIPERA, Steve15 and DOWNS, Gordon W.16, (1)Jacobs JETS Contract at NASA Johnson Space Center, Houston, TX 77058, (2)NASA Johnson Space Center, 2101 NASA Pkwy, Houston, TX 77058, (3)NASA Ames Research Center, Moffett Field, CA 945035, (4)Planetary Science Institute, Tucson, AZ 85719, (5)Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX 77058, (6)Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston, TX 77058, (7)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (8)NASA Goddard Space Flight Center, Greenbelt, MD 20771, (9)Lunar and Planetary Institute, Houston, TX 77058, (10)Geophysical Laboratory, Carnegie Institution, Washington, DC 20015, (11)Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058, (12)Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015, (13)Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, (14)NASA, Ames Research Center, MS 239-4, Bldg. 239, Rm. 321, Moffett Field, CA 94035-0001, (15)Chesapeake Energy, Oklahoma City, OK 73154, (16)University of Arizona, Tucson, AZ 85721


Characterizing the geochemical and mineralogical trends of the Murray formation, the lowermost unit of the Mt. Sharp group in Gale crater, is essential to interpreting ancient aqueous environments and post-depositional diagenetic alteration of this generally lacustrine sedimentary unit. To date, the Mars Science Laboratory Curiosity rover has drilled eleven samples from the Murray formation. Drilled sample fines were delivered to the CheMin instrument, a combination X-ray diffractometer and X-ray fluorescence spectrometer, and quantitative abundances of minerals and amorphous phases were determined.

Mineralogical Trends in the Murray Formation:

Mineralogical variations observed in the Murray formation include changes in abundance and speciation of Fe-oxides, sulfates, and phyllosilicates, reflecting changes in lake water chemistry and/or diagenetic conditions. At the base of the Murray fm. in the Pahrump Hills member, hematite, smectite, plagioclase, and pyroxene are the dominant mineral phases, indicating a basaltic igneous source for the sediments and relatively oxidizing aqueous conditions. Up-section ~10 m in the Pahrump Hills member, phyllosilicate is absent and plagioclase, cristobalite, tridymite, opaline silica, and magnetite are observed, suggesting a silicic igneous and/or hydrothermal source with more reducing aqueous conditions. Further up-section a few 10s of m, in the Hartmann’s Valley member, smectite re-emerges and is inferred to persist for at least a few 100 m of vertical section. The structure and composition of the smectite changes within the stratigraphy, where smectite has more dioctahedral character and is more enriched in Fe3+ and Al going up section into the Karasburg and Sutton Island members. Calcium sulfate and hematite abundances also increase significantly up-section. This change in mineralogy within the Murray formation indicates a greater intensity of near-surface chemical weathering and/or diagenesis over time.