Evidence for Multiple Diagenetic Episodes in Ancient Fluvial‐Lacustrine Sedimentary Rocks in Gale Crater, Mars.
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| Title: | Evidence for Multiple Diagenetic Episodes in Ancient Fluvial‐Lacustrine Sedimentary Rocks in Gale Crater, Mars. |
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| Authors: | Achilles, C. N.1 cherie.n.achilles@nasa.gov, Rampe, E. B.2, Downs, R. T.3, Bristow, T. F.4, Ming, D. W.2, Morris, R. V.2, Vaniman, D. T.5, Blake, D. F.4, Yen, A. S.6, McAdam, A. C.1, Sutter, B.7, Fedo, C. M.8, Gwizd, S.8, Thompson, L. M.9, Gellert, R.10, Morrison, S. M.11, Treiman, A. H.12, Crisp, J. A.6, Gabriel, T. S. J.13, Chipera, S. J.14 |
| Source: | Journal of Geophysical Research. Planets. Aug2020, Vol. 125 Issue 8, p1-20. 20p. |
| Subject Terms: | *Photochemistry, *Geomorphology, Homogeneity, Mineralogy, Fluid flow |
| Abstract: | The Curiosity rover's exploration of rocks and soils in Gale crater has provided diverse geochemical and mineralogical data sets, underscoring the complex geological history of the region. We report the crystalline, clay mineral, and amorphous phase distributions of four Gale crater rocks from an 80‐m stratigraphic interval. The mineralogy of the four samples is strongly influenced by aqueous alteration processes, including variations in water chemistries, redox, pH, and temperature. Localized hydrothermal events are evidenced by gray hematite and maturation of amorphous SiO2 to opal‐CT. Low‐temperature diagenetic events are associated with fluctuating lake levels, evaporative events, and groundwater infiltration. Among all mudstones analyzed in Gale crater, the diversity in diagenetic processes is primarily captured by the mineralogy and X‐ray amorphous chemistry of the drilled rocks. Variations indicate a transition from magnetite to hematite and an increase in matrix‐associated sulfates suggesting intensifying influence from oxic, diagenetic fluids upsection. Furthermore, diagenetic fluid pathways are shown to be strongly affected by unconformities and sedimentary transitions, as evidenced by the intensity of alteration inferred from the mineralogy of sediments sampled adjacent to stratigraphic contacts. Plain Language Summary: The mineralogy of mudstones and sandstones investigated by the Mars Science Laboratory rover illustrates a varied and complex history of aqueous alteration in Gale crater sediments. We present the mineralogy of four rocks determined by the CheMin X‐ray diffraction instrument onboard the rover. The results exhibit evidence of multiple diagenetic events, including aqueous alteration by warm groundwaters and a fluctuation of lake levels and evaporative events. Overall, the mineralogy of rocks sampled from the lowermost ~160 m of Gale crater stratigraphy explored by the Curiosity rover shows a decrease in Mg‐Fe‐silicates (i.e., olivine and pyroxene), a transition from magnetite to hematite, an increase in Ca‐sulfates, and a shift from Mg‐phyllosilicates to Al‐phyllosilicates. These trends imply an intensifying influence from oxic, diagenetic fluids. Furthermore, sites adjacent to unconformities and sedimentary transitions show more intense alteration suggesting that these physical boundaries play a key role in driving the path of diagenetic fluids. Key Points: CheMin‐determined mineralogy indicates pervasive low‐temperature diagenesis and localized hydrothermal alteration events at Gale craterThe diagenetic history of Gale crater is characterized by a diverse range in fluid chemistry, Eh, pH, and temperatureThe distribution of SiO2 and FeOT among crystalline and amorphous materials constrains the temperature and duration of diagenesis [ABSTRACT FROM AUTHOR] |
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| Database: | GreenFILE |
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