44-3 Preservation potential of organic molecules in Martian sediments altered by sulfate-rich brines

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part II

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Abstract:

Interpretations of preserved organic molecules and potential biosignatures in Martian sediments requires understanding both the initial preservation of organic matter and the effects of secondary processes (i.e., diagenesis). Clay-bearing lacustrine mudstones found in Gale Crater contain preserved organic molecules; however, the stratigraphically lowest mudstones contain more Fe-oxides and oxyhydroxides than those stratigraphically higher. Because these mudstones lie below sulfate-bearing units, it was proposed that concentrated MgSO₄·nH₂O brines interacted predominantly with the stratigraphically lowest mudstones, leading to clay mineral destruction and Fe-oxides/oxyhydroxide precipitation (Bristow et al., 2021). We hypothesize that this alteration leads to lower organic preservation potential in Martian sediments.

To test this, we conducted column flow-through experiments simulating MgSO₄ brine interactions with Martian-like sediments containing organic material. Sediments consisted of 30% nontronite (Nau-2) and 70% Teflon, reflecting the clay content of Gale mudstones. In one column, nontronite was pretreated with a 0.3 g/L solution of sodium alginic acid (polysaccharide produced by brown algae and microbial species) for one month. Controls included a Teflon-only column and no-sediment column. A 1.5 molal MgSO₄ solution was flowed through each column at 0.2 mL/hr for eight weeks (solution-to-rock ratio ~0.3 mL/g). Outflow was monitored for Fe, Si, Ca, Mg, and alginate.

Overall, Mg, Fe, and alginate concentrations remained steady at ~1 molal, < 0.1 ppm, and < 0.01 g/L respectively. In columns containing nontronite, Si concentrations peaked at ~10 ppm within 6 hours and then decreased to steady state values of ~0.5-0.8 ppm after 2 weeks, indicating clay dissolution. Additionally, Ca followed a similar trend but peaked at a higher value in the absence of alginate (415 vs 60 ppm), indicating that alginate influenced Ca mobility. The higher leaching rate of Ca than Si suggests that interlayer cation exchange was a dominate process; however, the absence of alginate in solution suggests either preferential binding to the nontronite or incorporation into a newly forming phase. Modelling with CrunchFlow predicts goethite precipitation, consistent with the low Fe in solution. The high Ca concentration indicates that calcium sulfate minerals may also precipitate. We are planning to look at the sediments from these experiments using electron microscopy, Raman spectroscopy, and X-ray diffraction, to assess what new phases are forming and if the alginate is being incorporated into these phases.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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