Constraining Alteration Processes Along the Siccar Point Group Unconformity, Gale Crater, Mars: Results from the Sample Analysis at Mars Instrument

Brad Sutter (1) , A.C. Mcadam (2) , G.M. Wong (3) , J.V. Clark (4) , P.D. Archer (1) , H.B. Franz (2) , P.J. Gasda (5) , D.W. Ming (4) , A. Yen (6) , J.M.T. Lewis (7) , S.P. Schwenzer (8) , S.M.R. Turner (8) , E.B. Rampe (4) , J.L. Eigenbrode (2) , J.C. Stern (2) , L.M. Thompson (9) , E. Dehouck (10) , C. Bedford (11) , S. Banham (12) , A.B. Bryk (13) , C. O’connell-Cooper (9) , C.S. House (3) , Maeva Millan (14, 2) , Caroline Freissinet (15) , R. Navarro-Gonzalez (16) , Paul R. Mahaffy (2) , C. A. Malespin (2)

1 Jacobs Technology ESCG
2 GSFC - NASA Goddard Space Flight Center
3 Penn State Department of Geosciences
4 JSC - NASA Johnson Space Center
5 LANL - Los Alamos National Laboratory
6 JPL - Jet Propulsion Laboratory
7 Department of Physics and Astronomy [Washington]
8 School of Environment, Earth and Ecosystem Sciences [Milton Keynes]
9 PASSC - Planetary and Space Science Centre
10 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
11 LPI - Lunar and Planetary Institute [Houston]
12 Department of Earth Science and Engineering [Imperial College London]
13 EPS - Department of Earth and Planetary Science [UC Berkeley]
14 Department of Biology [Washington]
15 PLANETO - LATMOS
16 Instituto de Ciencias Nucleares, UNAM

Results from the Sample Analysis at Mars (SAM)-evolved gas analyzer (EGA) on board the Mars Science Laboratory Curiosity rover constrained the alteration history and habitability potential of rocks sampled across the Siccar Point unconformity in Gale crater. The Glasgow member (Gm) mudstone just below the unconformity had evidence of acid sulfate or Si-poor brine alteration of Fe-smectite to Fe amorphous phases, leaching loss of Fe-Mg-sulfate and exchange of unfractionated sulfur ³⁴S (δ³⁴S=2±7‰) with enriched ³⁴S (20±5‰, V-CDT). Carbon abundances did not significantly change (322-661 μgC/g) consistent with carbon stabilization by amorphous Al- and Fe-hydroxide phases. The Gm mudstone had no detectable oxychlorine and extremely low nitrate. Nitrate (0.06 wt.% NO3), oxychlorine (0.13 wt% ClO4), high C (1472 μg C/g), and low Fe/Mg-sulfate concentration (0.24 wt.% SO3) depleted in ³⁴S (δ³⁴S = -27‰ ± 7), were detected in the Stimson formation (Sf) eolian sandstone above the unconformity. Redox disequilibrium through the detections of iron sulfide and sulfate supported limited aqueous processes in the Sf sandstone. Si-poor brines or acidic fluids altered the Gm mudstone just below the unconformity but did not alter underlying Gm mudstones further from the contact. Chemical differences between the Sf and Gm rocks suggested that fluid interaction was minimal between the Sf and Gm rocks. These results suggested that the Gm rocks were altered by subsurface fluids after the Sf placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations.

Domains: Sciences of the Universe [physics]

Brad Sutter, A.C. Mcadam, G.M. Wong, J.V. Clark, P.D. Archer, et al.. Constraining Alteration Processes Along the Siccar Point Group Unconformity, Gale Crater, Mars: Results from the Sample Analysis at Mars Instrument. Journal of Geophysical Research. Planets, 2022, 22 (11), pp.e2022JE007387. ⟨10.1029/2022JE007387⟩. ⟨insu-03850018⟩