Evidence for Multiple Diagenetic Episodes in Ancient Fluvial-Lacustrine Sedimentary Rocks in Gale Crater, Mars.

C N Achilles,P I Craig,T S Peretyazhko,L M Thompson,D T Vaniman,P Sarrazin,J P Grotzinger,A C Mcadam,S J Chipera,J A Crisp,S M Morrison,R Gellert,T S J Gabriel,G W Downs,A S Yen,D W Ming,M T Thorpe,R V Morris,E B Rampe,N Castle,T F Bristow,R C Walroth,C M Fedo,B Sutter,D F Blake,Robert T Downs ,Allan H Treiman ,V Tu ,Samantha Gwizd ,Robert M Hazen ,David J Des Marais ,John Michael Morookian

doi:10.1029/2019je006295

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.

Highlights

The Mars Science Laboratory (MSL) rover, Curiosity, has been exploring Gale crater since August 2012 with the primary goal of assessing environments that are, or once were, favorable habitats for life (Grotzinger ACHILLES ET AL.Journal of Geophysical Research: Planets10.1029/2019JE006295 et al, 2012)
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
APXS analyses of the Oudam, Marimba, Quela, and Sebina materials most representative of the powders analyzed by CheMin were acquired on Sols 1368, 1426, 1466, and 1496, respectively, and resulting data are listed in supporting information Table S1

Summary

Introduction

The Mars Science Laboratory (MSL) rover, Curiosity, has been exploring Gale crater since August 2012 with the primary goal of assessing environments that are, or once were, favorable habitats for life (Grotzinger ACHILLES ET AL.Journal of Geophysical Research: Planets10.1029/2019JE006295 et al, 2012). The change from phyllosilicate‐bearing sedimentary units at the base of Mount Sharp to sulfate‐bearing sedimentary units higher in the stratigraphy may signify an increase in aridity at ~3.5 Ga (Milliken et al, 2010) This phyllosilicate to sulfate stratigraphy has been recognized from orbital visible/short‐wave reflectance measurements across the planet (e.g., Bibring et al, 2006; Bishop & Rampe, 2016; Bishop et al, 2008; Carter et al, 2015; Deit et al, 2012; Ehlmann et al, 2011; Wiseman et al, 2010), suggesting a global climate change early in Mars' history. Curiosity has climbed the lower layers of Mount Sharp, investigating sedimentology, mineralogy, and geochemistry to characterize the environments preserved by the rocks and to evaluate evidence of past habitable conditions and local, regional, or global indicators of climate change

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