¹W. Rapin (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009783
Open Access Link to Article [DOI: 10.1029/2026JE009783]
¹Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS UMR 5277, CNES, Toulouse, France

Published by arrangement with John Wiley & Sons

Changing surface conditions on Mars during the Hesperian eon (∼3.6–3.0 billion years ago) produced widespread stratal sequences transitioning from clay to sulfate-bearing according to orbital data. Using data collected in situ at Gale crater by the Curiosity rover, we examined both the sedimentology and geochemistry of a 210-m-thick succession across a reference clay-sulfate transition. Four intervals (A–D) are defined based on both sedimentary structures and nodule distribution and composition, reflecting changes in depositional setting and diagenetic parameters. Large trough cross-beds, which become prevalent within interval A and dominate intervals B and C, are interpreted to indicate eolian processes, whereas dark-toned lens-shaped sandstone bodies in interval C point to recurring fluvial incursions. Planar bedding in uppermost interval D suggests damp or wet interdune conditions. ChemCam analyses show nodules are enriched in calcium and magnesium sulfates. The highest observed nodule densities coincides with strata interpreted to reflect damp or wet depositional environments (A, C, D), whereas their near-absence corresponds to the interval interpreted as the driest (B). We propose that this stratigraphic partitioning of the type, density, and sulfate-content of nodules indicates that they mostly formed during early diagenesis via capillary evaporation in the shallow subsurface, with only subordinate late-stage remobilization. The preserved strata record fluctuations in water availability and sediment supply, driven by repeated changes in climate, rather than by a single drying trend. These observations suggest new constraints on the fate of sulfur on early Mars and sulfate evaporite formation within sedimentary basins.

¹Hunter Vannier, ¹Briony H. N. Horgan, ²Michael Phillips, ¹Michael Eddy, ³Rebecca Greenberger, ⁴Arya Udry
Journal of Geophysical Research: Planets, 131, e2026JE009705
Open Access Link to Article [DOI: 10.1029/2026JE009705]
¹Purdue University, West Lafayette, IN, USA
²University of Arizona, Tucson, AZ, USA
³California Institute of Technology, Pasadena, CA, USA
⁴University of Nevada Las Vegas, Las Vegas, NV, USA

Published by arrangement with John Wiley & Sons

Widespread plagioclase detections on Mars using orbital visible to near infrared (VNIR) reflectance spectra have led to multiple interpretations of “feldspathic” terrain, ranging from ancient crustal material and evolved plutons to volcanic lava flows. A systematic, laboratory-based study of plagioclase detectability in whole igneous rocks is needed to contextualize these detections. We analyzed 42 feldspar-bearing igneous rocks (∼50–77 wt.% SiO₂; ∼25–60 vol.% plagioclase) using VNIR and mid-infrared (MIR) laboratory spectra, bulk chemistry/mineralogy, microscopic analyses of rock texture, and plagioclase chemistry to assess the characteristics influencing plagioclase signatures in whole-rock spectra. We find that 1.25 μm absorption bands are common in intrusive samples, and that plagioclase can be spectrally detected at abundances <40 vol.%, even in the presence of ∼20 vol.% mafic hydrous minerals. We find that large (mm-scale) grain size is a driver of plagioclase detection, and that oxides are highly effective at subduing absorption bands. Plagioclase with a wide range of compositions (An_25–47,90) can produce a 1.25 μm absorption, unless iron-depleted (<0.13 wt.% FeO). Alteration can obscure the 1.25 μm absorption, causing rocks with similar plagioclase abundances and chemistries to exhibit different bulk VNIR spectra. Unambiguous detection of feldspathic rocks on Mars is only likely for: (a) plagioclase-rich crust (e.g., anorthosites or other plagioclase cumulates), (b) intrusive felsic rocks with limited alteration and plagioclase with iron >0.13 wt.%, and (c) plagioclase-phyric effusive rocks with little or no mafic phenocrysts. MIR spectra can distinguish felsic (granite, granodiorite, monzonite) and mafic (anorthosite, basalts) rocks with similar 1.25 μm absorptions.