In Situ Carbonation of Sedimentary and Igneous Rocks of Ultramafic Composition in Jezero Crater, Mars

Over 3.5 years of exploration in Jezero Crater, the Perseverance rover has explored several geological units of diverse origins and natures, performing multi-technique remote analyses of the chemistry and mineralogy of rocks with the SuperCam instrument suite.

Three of these units are dominated by mafic to ultramafic rocks: the igneous rocks of Séítah (olivine cumulate on the crater floor), the sedimentary rocks of the Upper Fan (Western delta) and the Margin Unit, of likely igneous origin.

Despite their diverse natures, these three different units present similar mineralogical assemblages with: (a) primary igneous minerals (olivine, pyroxene, Cr-rich Ti-Fe oxides), (b) Fe-Mg carbonate, (c) hydrated/hydroxylated silica, and (d) phyllosilicates. The abundance of carbonate is variable, and we estimate it around 3–9 wt.% and up to 6–16 wt.% carbonate mineral in the Upper Fan and Margin Unit, respectively.

We propose that most of these carbonates formed through in situ carbonation of mafic/ultramafic material, whether these rocks were emplaced through igneous or sedimentary processes. The distribution of carbonate with elevation in the Upper Fan and Margin Unit suggests a contribution of the lacustrine activity to the carbonate process, possibly enhanced by hydrothermal activity.

These in situ observations may be extrapolated to other carbonates-bearing rocks on Mars and would make the amount of carbon potentially stored in Martian ultramafic rocks overall significant. This would suggest that carbonation of ultramafic rocks might have played a key role in pumping CO2 from and therefore in cooling the Martian atmosphere.

Representative outcrops of the Jezero western delta in which carbonates have been detected. (a) Mastcam-Z image of the base of the delta with the Rockytop outcrop within the 6 m high scarp (sol 429, zcam08452) located at the base of the Tenby formation immediately overlying the Hogwallow Flats light-toned deposits. The white arrow indicates the fallen block where the SuperCam target Fourway has been analyzed. (b) Close-up on the SuperCam target Fourway (sol 407, scam01407, Gaussian stretch). The texture is that of a coarse sandstone to granule-conglomerate containing rounded, subrounded and subangular grains. (c) Mastcam-Z mosaic (sol 743, zcam08747) of Tenby outcrop, which is part of the Tenby formation. The white box indicates the location of detail (d). (d) SuperCam RMI of the Crymych target (sol 745, seq04745, gaussian stretch). The Tenby outcrop displays coarse sandstones with local granules and pebbles exposed in steeply dipping beds. Red circles represent fields-of-view of infrared spectrometer observations. (e) Outcrop Onahu (sol 781, scam01781) in the Otis Peak formation, overlying the Tenby formation. The strongly weathered outcrop of this formation is composed of pebbly sandstones and conglomerates (5 cm pebble with a white arrow). (f) Target Ouzel_Falls (sol 791, scam01791) located nearby Onahu displaying several mm large clasts with various degrees of rounding. Yellow arrows indicate some of the local most visible rounded or subrounded mm-size granules. — JGR Planets

In Situ Carbonation of Sedimentary and Igneous Rocks of Ultramafic Composition in Jezero Crater, Mars, JGR Planets (open access)

Astrobiology, Astrogeology,