# Recent aqueous alteration associated to sedimentary volcanism on Mars

M. Pineau, J. Carter, A. Lagain, E. Ravier, N. Mangold, L. Le Deit, C.

Quantin-Nataf, A. Zanella

► To cite this version:

M. Pineau, J. Carter, A. Lagain, E. Ravier, N. Mangold, et al. Recent aqueous alteration associated to sedimentary volcanism on Mars. Communications Earth & Environment, 2025, 6 (1), pp.800. 10.1038/s43247-025-02713-3. hal-05306001

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# Recent aqueous alteration associated to sedimentary volcanism on Mars

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M. Pineau Ⓟ<fnref n="1" />,²✉, J. Carter Ⓟ<fnref n="1" />,³, A. Lagain Ⓟ⁴,⁵,⁶, E. Ravier Ⓟ⁷, N. Mangold Ⓟ⁸, L. Le Deit Ⓟ⁸, C. Quantin-Nataf Ⓟ² & A. Zanella Ⓟ⁷

Sedimentary volcanism, whereby material is brought to the surface by fluid overpressure, has been proposed to explain some of the periglacial landforms, including pitted cones, in the Northern Plains of Mars. However, in the absence of convincing mineralogical evidence, the origin for these deposits has never been conclusively determined. Here we conduct a remote sensing-based mineralogical survey to identify hydrated minerals within the Thumbprint Terrains and neighbouring Vastitas Borealis Formation. We detect several occurrences of hydrated silica along with sulfate salts in candidate mud volcano-like morphologies which likely formed during the Early Amazonian period, supporting the sedimentary volcanism origin. Buoyancy-driven analytical modelling suggests the hydrated silica and sulfate salts are sourced from reservoirs at depths of several 10 s and 100 s of metres, respectively below the Thumbprint Terrains and Vastitas Borealis Formation. The exposed sulfates may have been derived from ancient buried evaporite deposits suggesting, at least locally, a salt-rich aqueous origin for the Vastitas Borealis Formation, and would be consistent with the presence of a past northern ocean on Mars.

The Noachian (4.1–3.8 Ga) is a geological period where comparatively warmer and wetter climates enabled at least intermittently liquid water to chemically modify the crust of Mars<fnref n="1" />⁻³. Around the Noachian-Hesperian transition (3.8–3.6 Ga), Mars has undergone a loss of its atmosphere, declining surface water activity, and experienced increasingly arid and cold climates<fnref n="1" />,⁴. However, there is an emerging perception that the Martian hydrosphere, while waning since the Hesperian, may have been able to persist and occasionally leave behind traces of aqueous activity well into the Hesperian and perhaps even later during the Amazonian (<3.1 Ga)⁵⁻¹³. There is however little indication for late-stage surface water activity, especially in the lowlands and Northern Plains (NPs) of Mars, which are the dominant Amazonian units¹⁴. Exploration of the young NPs has the potential to answer key questions regarding the fate of water on Mars and the timing of its activity, including the presence of lingering subsurface aqueous reservoirs that have not been subject to atmospheric escape¹⁵. Quantitatively, such reservoirs remain poorly constrained for lack of direct evidence. Their ability to have been remobilized in liquid form at or below the surface is also a critical knowledge gap because this would imply a heightened habitability potential for recent Mars¹⁶, as well as provide anchor

points in the Mars timeline with respect to the stability of water in the near subsurface and surface.

To address these questions, we conducted a mineralogical survey of the NPs in search of specific tracers of aqueous activity. We focused our survey on the Late-Hesperian to Early-Amazonian “Vastitas Borealis Formation” (VBF), which has been dated to 3.75–3.40 Ga¹⁷⁻¹⁹ (Fig. 1). The VBF has been interpreted as a depositional unit resulting from outflow channel floods or an ancient hydrological reservoir²⁰,²¹ (Fig. 1A). In regions such as Acidalia, Utopia, Isidis and Chryse Planitiae, the VBF is associated with the striking morphological unit called the Thumbprint Terrains (TT) that exhibits sets of parallel ridges and curvilinear features overprinted by clusters or chains of pitted cones and mounds²²,²³. Several hypotheses have been proposed for the TT formation, among others: explosive volcanism resulting in cinder cones, pseudo-craters²⁴ or glacial processes resulting in pingos and moraines²²,²⁵. Others suggest the presence of mudflows coupled with mud volcanism²⁶⁻²⁹. Impact-generated tsunami deposits in a Hesperian-Amazonian paleo-ocean were also proposed³⁰⁻³³, in agreement with Parker et al. (1993) hypothesis³⁴. While these features are suggestive of water activity, conclusive compositional evidence was lacking as no hydrated minerals were detected

<footnote n="1">¹Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France. ²Univ Lyon, Univ Lyon 1, ENSL, CNRS, LGL-TPE, Villeurbanne, France. ³Institut d'Astrophysique Spatiale, Univ Paris Sud, CNRS, Univ Paris-Saclay, Orsay, France. ⁴Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France. ⁵Aix-Marseille Univ, Institut ORIGINES, Marseille, France. ⁶Space Science and Technology Centre, School of Earth and Planetary Science, Curtin Univ., Perth, Australia. ⁷Laboratoire de Planétologie et Géosciences, LPG UMR 6112, CNRS, Le Mans Université, Univ Angers, Nantes Université, Le Mans, France. ⁸Nantes Université, Univ Angers, Le Mans Université, CNRS, Laboratoire de Planétologie et Géosciences, LPG UMR 6112, Nantes, France. ✉e-mail: maxime.pineau@univ-lyon1.fr</footnote>
**Fig. 1 | Locations of the area investigated in this study at the surface of Mars.** A Global map of Mars showing locations where hydrated phases are detected in this study (red boxes) zoomed in (B). for Acidalia region, and (C). for Utopia Region. Basemap is global MOLA topographic map. Regions mapped in light blue represent the extension of the Vastitas Borealis Formation units¹³⁰. Regions outlined in light grey with dashed outlines are areas with proposed sedimentary volcanism on Mars²⁹.

B Location of CRISM cubes with HySi and PHS detections (white and red circles, associated with CRISM IDs) in Acidalia Planitia. Basemap is THE-MIS Day IR overprinted with geological units from Tanaka et al. (2014)¹⁴. C Location of CRISM cubes with HySi and PHS detections in Utopia Planitia.

Basemap is THEMIS Day IR overprinted with MOLA elevation. In this context, the entire area lies within the same “IHI” geological unit, which is the most widespread in the NPs¹⁴ (also visible in B).

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(Supplementary Text 1). In turn, no precise formation mechanism explaining such morphologies was available.

## Summarized methods

Our survey was driven by remote sensing data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)³⁵ onboard the Mars

Reconnaissance Orbiter (MRO) spacecraft. Expanding from a coarser survey across the entire surface of the planet¹², we relied on high-resolution observations (spatial resolution <40 m/pixel), searching for hydrated mineral spectral signatures as tracers of aqueous alteration. The geomorphological context of each mineral detection was ascertained by combining ortho-rectified CRISM mineral maps with orbital imagery from the Context
<figure><img src="image_5.png" /><figcaption>**Fig. 2** | Examples of CRISM detections of hydrated phases in association with sedimentary volcanism edifices in Acidalia and Utopia Planitia. Mineral detections: cyan for HySi, green for PHS, red for Fe/Mg-clays. Acidalia Planitia detections: A–D. Utopia Planitia detections: E, F. Lat./Long. details: A 41° 38′ N, 5° 20′ W; B 45° 12′ N, 5° 10′ E; C 40° 00′ N, 7° 30′ W; D 44° 40′ N, 8° 27′ E; E 31° 30′ N, 96° 20′ E; F 30°35′N, 97°40′E. White box in A is displayed in Fig. 3 (FRT0000A386 (2) inset).</figcaption></figure>

Black box in **B** is displayed in Fig. 5. Close-up views of the PHS-rich mound and flow features, and HySi-rich cones and ridges present in **F** are displayed in Fig. 7. For each image, background is a combination of CTX image overlined by CTX Digital Elevation Model (increasing elevation from shades of blue to red), except for **B**. where background is a CaSSIS image. North is up in each image.

Camera (CTX)³⁶, the High-Resolution Imaging Science Experiment (HiRISE)³⁷ as well as the Colour and Stereo Surface Imaging System (CaSSIS)³⁸. We also estimate grain sizes at the surface based on models of thermal inertia (TI) of the surfaces derived from Mars Odyssey's Thermal Emission Imaging System (THEMIS)³⁹. Surface ages were also estimated by model age standard crater counting. The methods are detailed in Methods section and Supplementary Text 2.

## Detection of hydrated minerals

In the TT of Acidalia (Fig. 1B), we detected hydrated (opaline) silica (HySi) and some poly-hydrated sulfates (PHS) associated with geomorphologies reminiscent of sedimentary extrusion. Examples of different sites are shown in Fig. 2A–D, with close-up views in Fig. 3 (see Supplementary Fig. 1 for projected CRISM images with minerals detections). CRISM spectra examples are displayed in Fig. 4 (detection description are detailed in Supplementary Data 1). Only one site exhibits a weak Fe/Mg-phylosilicate exposure partially mixed with HySi (Fig. 2A). No site exhibit carbonates, zeolites or other high-temperature hydrated minerals. This contrasts with what is more commonly found within large NP impact craters which have been found to excavate km-deep buried material, and occasionally shown evidence for impact-induced hydrothermal systems⁴⁰,⁴¹. We found no igneous mineral signatures of olivine and pyroxene that would be expected in Mars igneous volcanic settings, which is also supported by the low TI of the features (Supplementary Data 2). The TI values are compatible with fine-grained sedimentary materials²⁶,³¹,³³,⁴².

HySi is found within the TT to be associated with 10 s of cones which are several meters high, and at times feature a pitted summit. HySi is preferentially found on the cone summits (Fig. 2A–D; Fig. 3; Supplementary Fig. 1). Figure 2A also shows HySi as surficial fine-grained materials that are eroded or expelled from the nearby cones. Despite this

example, for most HySi-bearing cones, no obvious extensive flow-like features are observed. While CRISM data do not show systematic detections of hydrated minerals on all cones, the shared similarities between CRISM-based detections and cones and others observed in HiRISE and CaSSIS images (textures, grain-sizes, colour hues) do suggest that many more pitted cones and related surrounding material in the region could contain HySi. In rare cases, small impact craters exhuming the flanks of cones give us a glimpse into their internal hydrated composition (Fig. 3, FRT0000A386 (2) inset).

In contrast to HySi, PHS are located in morphologically young impact craters, where the strongest signatures are in their flanks and ejecta deposits (Fig. 2A, C, D; Supplementary Fig. 1). These craters, ranging from 300 m to 3 km in diameter, generally present lobate ejecta suggesting that they impacted volatile-rich material⁴³. Another context for PHS is illustrated in Fig. 2B which displays PHS detections in association with a large 165 meters-high mound (unpitted) with HySi at its base. At least two well-preserved fractures are observed, out of which material may have spewed downhill from the mound (Fig. 5).

Similar mineralogy with similar associated contexts can be found far apart (7000 km) in Utopia at two locations (Fig. 1C; Fig.2E, F; Fig. 6; Supplementary Fig. 2). Here, PHS are found in association with a large 350 meters-high asymmetric bright-toned and unpitted mound, which summit exhibits meter-scale boulder-rich layering (Fig. 2F; Fig. 7A, B). A specificity here, radial viscous flow-like features that are several kilometres long seem to have spewed from it, and these also exhibit PHS signatures (Fig. 2F; Fig. 7A, C, D, E). By contrast to PHS, HySi detections are located within several neighbouring bright-toned sinuous “curvilinear” ridges. These are several kms long, and exhibit within them chains of pitted cones. These ridges are also associated with a neighbouring pitted cones field exhibiting HySi signatures (Fig. 2F; Fig. 7F, G).
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**Fig. 3** | Close-up views of HySi-rich deposits in the Acidalia Planitia region. For each item, the corresponding CRISM cube is indicated. From top left to bottom right item: FRT0000A1F4, HySi-bearing pitted cones (pointed with black arrows), CRISM HySi detections in cyan overprinted on a CTX image and its associated DTM; FRT0000A386 (1), HySi-bearing pitted cones in a HiRISE image and its associated DTM. Black arrows point toward HySi detection; FRT0000A386 (2), impact crater with a slice in the flank of a pitted cone, allowing observation of the cone's internal structures. Outlined by black dotted lines, these internal structures show boulder-rich materials whose blue-turquoise hues in the HiRISE IRB image may reflect the presence of hydrated materials; FRT00008787, CRISM HySi detections in cyan in

pitted cones (pointed with white arrows) on a CTX image and its associated DTM; FRT000173F1, HySi-rich pitted cones view in a CTX image (pointed with black arrows); HRL0000B4C4, CRISM HySi (cyan) and sulfates (green) detections overprinted on a CTX image in close association with a pitted cone (white arrow) and a tear-shaped butte; HRS0000C189, CTX close-up view of the pitted cone with HySi on its flank (CRISM detection in cyan); FRT00009E68, HiRISE close-up view of the HySi-bearing pitted cones in chains (pointed with black arrows); FRS000363C5, CRISM HySi detection (black arrow) on a pitted cone, overprinted on a CTX image and its associated DTM. North is up in each image.

## In-depth spectral characterization of the minerals

Our main finding is the presence of widespread detections of HySi within and around pitted cones. Their nature and origin can be further inferred from the type of silica and geochemical conditions in which they have formed. To do this, we used spectral discrimination criteria on the CRISM data that are adapted to HySi spectral signature¹⁴⁻⁴⁷: the minima position of their absorption bands, their relative area, and their shape using the Concavity-Ratio-Criterion (CRC) (see Methods and Supplementary Text 3). The results of these spectral criteria can be visualized and readily

interpreted in diagrams as shown in Fig. 8 (details in Supplementary Text 3, 4 and Supplementary Data 1, 3).

In the diagram of Fig. 8A, observations fall within the bottom-left corner that is characteristic of HySi formed through low-temperature (low-T) geological processes (T < 60 °C) such as surface weathering or low-T hydrothermal activity if we consider that the dehydration was limited, which is unfortunately impossible to verify with current orbital instruments. The data also fall in the cluster that is indicative of rather poorly hydrated or dehydrated varieties of HySi.
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**Fig. 4** | Examples of CRISM spectra for HySi-rich and PHS-rich materials in the **Acidalia Planitia** region. For each diagram, CRISM spectra (HySi-rich in blue, diagram A.; PHS-rich in green, diagram B) are compared to terrestrial analogues in black: 1. obsidian, 2. chalcedony, 3. opal-CT, 4. opal-A for (A); 1. jarosite, 2. alunite, 3. bassanite, 4. szomolnokite, 5. kieserite, 6. gypsum, 7. starkeyite for panel B. For each diagram, main diagnostic absorptions of the HySi/sulfate minerals are

indicated as vertical grey lines. CRISM spectra are labelled following corresponding CRISM cube; in A. 1. FRT00009E68, 2. FRS000363C5, 3. HRS0000C189, 4. HRL0000B4C4, 5. FRT00008787, 6. FRT0000A1F4, 7. FRT0000A386, 8. FRT000173F1; in B. 1. FRT0000A386, 2. HRL0000B4C4, 3. FRT0000A1F4, 4. FRT000173F1, 5. FRT00009E68.

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**Fig. 5** | Close-up views of the Acidalia PHS-rich mound. A HiRISE RED & IRB images close-up views of the PHS-rich Acidalia mound (PHS CRISM detections in green) with HySi (in cyan) at its base located at coordinates 45°12′N, 5°10′E. B HiRISE close-up view of the fractures (pointed with white arrows) in close

association with PHS-rich materials. C HiRISE IRB image of the fractures filled with hydrated materials as indicated by blue-turquoise hues in HiRISE IRB image (pointed by white arrows). North is up in each image.

In the truncated ternary diagram in Fig. 8B, HySi detections associated with pitted cones exhibit properties diagnostic of poorly-hydrated silica (e.g., volcanic glasses or chalcedony) and/or moderately to highly dehydrated species (opal-A/CT under Mars atmospheric conditions), the data points have an intermediate position between the two clusters.

Considering these spectral observations, we favour the presence of poorly hydrated HySi varieties, mostly in an amorphous state, such as silica gels, altered volcanic glasses (e.g., fine-grained altered ashes or pumices), or HySi-rich silt-to-sand material that underwent low-T aqueous alteration

and/or water-limited fluid-rock interaction. Essentially, we rule out hydrothermal alteration as their likely origin.

While the detection of PHS-rich deposits associated to impact craters and large mounds is straightforward, it is unfortunately difficult to assess their precise composition. Indeed, PHS spectra observed in the CRISM spectral range lack sufficient features to make a precise identification, other than the generic absorptions at 1.4, 1.9 and 2.4 µm (e.g., ref. 48; Figs. 4, 6). These generally agree with Ca- or Mg-rich poly-hydrated salts. We can confidently exclude Fe-rich salts, hydroxylated sulfates such as jarosite or alunite, or hydrated chlorinated salts.
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**Fig. 6 | HySi and PHS detections in the Utopia Planitia region and corresponding CRISM spectra.** A, B HySi (cyan) and PHS (green) detections in two projected CRISM images in the Utopia Planitia region. For each item, CRISM ID is provided with lat/long coordinates. North is up in each image. Close-up views of the HySi-rich pitted cones field in A. are displayed in Supplementary Fig. 2. C, D. display examples of CRISM spectra for HySi-rich materials (in blue, diagram C) and PHS-rich materials (in green, diagram D) in Utopia. For each diagram, CRISM spectra are

compared to terrestrial analogues in black: 1. obsidian, 2. chalcedony, 3. opal-CT, 4. opal-A for panel C.; 1. jarosite, 2. alunite, 3. bassanite, 4. szomolnokite, 5. kieserite, 6. gypsum, 7. starkeyite for (D). For each diagram, main diagnostic absorptions of the HySi/sulfate minerals are indicated as vertical grey lines. CRISM spectra are labelled following corresponding CRISM cube; in A. 1. to 3. FRT00017498, 4. to 6. FRS0003BE9F; in B. 1. and 2. FRT00017498.

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**Fig. 7 | HySi-rich and PHS-rich geomorphologies in the Utopia Planitia region.**
A PHS (green) and HySi (cyan) detections in the projected CRISM cube FRT00017498 (in Utopia Planitia). B HiRISE close-up view of the PHS-rich mound showing brecciated-like layered materials made of metre-sized boulders. C HiRISE close-up view of PHS detections (black arrows) in a lobate flow-like features W of the PHS-rich mound. D HiRISE close-up view of a similar kilometre-long lobate flow-like feature SE of the PHS-rich mound that also shows PHS detections pointed with

black arrows. E IRB HiRISE close-up view of a portion of the SE flow-like lobe that exhibits possible hydrated debris-rich layers at its base as indicated by blue tones. F HiRISE close-up view of the HySi-bearing pitted cones and HySi-rich sinuous ridge NE of the PHS-rich cone. Black arrows point toward HySi detections. Note that one pitted cone may exhibit PHS occurrence. G IRB HiRISE close-up view of bright-toned pitted cones that sometimes exhibit multiple somital depressions; one pitted cone is HySi-rich (black arrow). North is up in each image.

## Characteristics and origin of sedimentary volcanism

Our datasets demonstrate that the pitted cones, previously interpreted as mud volcano-like structures on the basis of morphology only²⁹, can be confidently linked to the presence of hydrated minerals supporting an origin

by sedimentary volcanism. On Earth, the mineralogy observed at the surface of sedimentary volcanoes depends on the lithology of the buried source (e.g., clay-rich versus sand-rich) and the composition of the fluids accompanying the remobilized sediments. In terms of alteration mineralogy, with a notable
<figure><img src="image_11.png" /><figcaption>**Fig. 8 |** Classification diagrams of the spectral criteria calculated on HySi CRISM detections in Acidalia and Utopia Planitiae. A CRC of the 1.9 µm absorption versus CRC of the 1.4 µm absorption. Small triangles are calculated on individual spectra (error bars = 1 standard error), while large triangles are mean values of criteria on all spectra extracted for the same zone (error bars = 1 standard error).</figcaption></figure>

B Contribution of each absorption band displayed as a ternary diagram. The different fields in the two items were defined on terrestrial analogues⁴⁴⁻⁴⁷ (see Supplementary Text 3). See main text for interpretation. The smaller number of data in the diagram in A is due to the fact that some CRC values have not been kept (two CRC values are required for a data item to be represented in A).

NIR signature, terrestrial mud volcanoes would show a composition dominated by phyllosilicates (micas, smectites, kaolins), carbonates, sulfates and a low-to-moderate amount of amorphous phase (e.g., HySi)⁴⁹⁻⁵¹. Injectites, extrudites and sand volcanoes, with coarser particles, are rather enriched in carbonates, clays, micas, and siliceous cements (e.g., chalcedony, HySi)⁵²⁻⁵⁴. The mineralogy we observe on Mars is devoid of clays and carbonates, thus different from that expected for terrestrial mud volcanoes. We investigate below all stages of the proposed sedimentary volcanism process: the nature and origin of the source material, the intrusion mechanism, and the extrusion conditions.

## HySi formation and source reservoirs depths

In the context of sedimentary volcanism, several hypotheses could explain the HySi occurrence: i) pre-existing and pre-altered buried Si-rich sediments (such as altered ashes or pumices, silts or sands), ii) formation of aqueous minerals through alteration of Si-rich sediments during upwelling, or iii) formation at the surface after emplacement, iv) direct HySi precipitation

from Si-saturated fluids reaching the surface. The process of aqueous alteration may or may not have been coeval with the upwelling process of the fluidized HySi reservoirs.

In the context of continental alteration by surface agents, we would expect the formation of hydrated phases over large areas and not localized in the pitted cones and observed ridges. This hypothesis is not consistent with the observations and therefore is ruled out. Instead, we propose that the surface occurrences of HySi are linked to the upwelling of sediments and fluids to the surface by sedimentary volcanism. This may have occurred from the extrusion of buried HySi-bearing sediments, and/or by direct precipitation of HySi from siliceous fluids.

Although it is difficult to estimate the amount of fluid associated with HySi precipitation, its presence is indicative of siliceous solutions from which HySi gels were formed. It is also possible to propose that pre-existing subsurface HySi-rich materials were extruded. Such types of Si-rich cones may be indicative of clastic pipe-like features³²,⁵⁵,⁵⁶ such as in terrestrial sand-rich sedimentary volcanoes³³,⁵⁷⁻⁶¹ and/or hydrodynamic blowouts⁶²⁻⁶⁵. In the
<figure><img src="image_12.png" /><figcaption>**Fig. 9** | Interpretative sketches displaying the stratigraphic relations between HySi/PHS-bearing cones and surrounding TT-VBF units in Acidalia Planitia (top) and Utopia Planitia (bottom). For the PHS-rich mound with HySi at its base in Acidalia, the proposed scenario is that PHS were extruded from deep VBF layers and incorporated HySi-rich materials or Si-fluid present in the TT lithologies during</figcaption></figure>

their ascent to the surface. The Utopia sites are not associated with TT formation and therefore attest to the presence of HySi-PHS-rich materials or fluids in VBF units too. The proposed scenario is that of upwelling by pure sedimentary volcanism (for cones) or along faults (for ridges) of materials or fluids present in the subsurface as silica-rich reservoirs. Note that for all items, scales are not respected.

latter case the HySi sources are constrained by the thickness of the TT (< 100 m³¹,⁶⁶) and therefore may be shallow.

We assess the depth of the sourced materials using a buoyancy-driven upwelling model applied to sedimentary volcanism⁶⁷,⁶⁸ (see Methods, Supplementary Text 5, and Supplementary Data 4). Given the limits allowed by the assumed thickness of the TT (< 100 m³¹,⁶⁶), and whatever the considered densities for extruded materials and host rocks, we found that HySi-rich materials are sourced from several 10 s of meters underground (between 10 to 80 m), from subsurface reservoirs that are internal to the TT. Regarding other HySi-rich cones outside the TT, depths are less well constrained, but are likely ranging from a few tens of meters to a maximum of 200–300 m. These depths, in agreement with previous estimates⁶⁸,⁶⁹, attest to the presence of HySi-rich lithologies or siliceous aqueous reservoirs within the TT units (Fig. 9, top), but also to a possible presence of similar HySi-bearing sediments in the older VBF units. The latter is based on HySi detections in cones outside the TT, for example in Utopia Planitia (Fig. 9, bottom).

## PHS formation and source reservoirs depths

PHS are in majority associated with impact craters with diameters ~1-3 km or less, and must have been formed through the excavation and subsequent sublimation of salt-rich ice in the regolith⁷⁰. However, such small impacts also excavate materials beyond 80-90 meters depth⁷¹. In this case, the presence of PHS may indicate sulfate-rich reservoirs in the TT subsurface and/or in the surrounding/underlying VBF unit (Fig. 9, top). This could be

inferred from observations where different impacts excavate PHS-rich materials in different settings (Fig. 2A,C,D,F).

PHS are also observed in association with the large Acidalia and Utopia mounds (Fig. 2B, F; Fig. 5; Fig. 7). Following the same rationale as for HySi formation, we rule out sulfate formation from regional continental weathering, and the positive topography excludes playa-like evaporitic settings. We discuss PHS formation through fluid-rich sedimentary volcanism independently for the Acidalia and Utopia edifices.

Regarding Acidalia, no flow feature is observed. Thus, this PHS-rich mound may have formed through sedimentary volcanism involving low amounts of fluid. The presence of surface fractures indicates possible gas-rich extrusion (Fig. 5). This could be indicative of PHS formation in fumarolic-like setting, but this hypothesis is not supported by the amagmatic geological context and mineralogy. Gas is common in terrestrial sedimentary volcanism as fluid overpressure of volatile-bearing sediments will be the main trigger of the extrusion²⁹,⁵⁰,⁵⁵,⁷². Here again, the presence of pre-existing subsurface sulfates that were extruded through gas-rich (possibly explosive but unconfirmed here⁷³⁻⁷⁵) sedimentary volcanism is the most favoured hypothesis (Fig. 9, top). The boulder-rich nature of the materials constituting the mound is also in line with this (Fig. 5). When sedimentary volcanism occurs, it is common to have remobilization and incorporation of the intersected layers by the injected materials, resulting in a brecciated mixture of different lithologies²⁹,⁷²,⁷⁶,⁷⁷. The presence of HySi in the basal part of the cone from silica intake
**Fig. 10** | Normalized probability density function of ages summarizing crater-count dating results for the TT lobes surfaces (Sx) in Acidalia (top) and VBF units in Utopia (bottom) regions. For the Acidalia region, considering larger error bars for lowest model ages, regardless of whether individual surfaces (top diagram) or combinations (middle item) of these are considered, we favour a common formation for all TT lobes towards 2.0–2.6 Ga during the Early Amazonian; the sedimentary volcanism events likely formed later this model age of retention. For the Utopia region, all results (bottom diagram) point toward model age of retention in the middle age of the Early Amazonian period, with model ages spanning from 2.1 to 2.7 Ga. For detailed information see Supplementary Text 6.

<figure><img src="image_13.png" /></figure>

within the rising materials during the sedimentary volcanism activity is a case in point (Fig. 2B; Fig. 9, top).

In Utopia, geomorphological observations support more fluid-rich activity compared to Acidalia. The observation of radially extending surface flow features with PHS detections (Fig. 2F; Fig. 7) may indicate that the sedimentary volcanism context here is accompanied with higher fluid quantities (Fig. 9, bottom). The PHS in the flow features could represent detrital sulfate-rich materials remobilized from the cone or sulfates formed through evaporation of upwelled saline waters stagnating in ponds⁷⁸. We do not observe ponding/evaporitic features such as small depressions or basin-like morphologies that may have been able to sustain stagnant salty waters. A more likely explanation would be that the mound represents upwelled sulfate-rich materials in an intrusive context, indicating that the subsurface may contain a deep salt-rich reservoir⁷⁹⁻⁸¹ (Fig. 9, bottom).

Applying the same buoyancy-driven model to the PHS-rich mounds and cones of Acidalia and Utopia Planitiae respectively, we found that the PHS sources are 100 s meters deeper than the HySi sources, reaching up to a few kilometres. Their origin is therefore linked to deeper geological reservoirs within the VBF units (Supplementary Text 5; Fig. 9). These results are in the predicted ranges for Martian edifices⁶⁹ and would imply the presence of sulfate salt-rich lithologies within the VBF layers (Fig. 9), possibly in the form of ancient evaporites.

## Mechanism triggering sedimentary volcanism

The mechanisms that triggered the sedimentary volcanism responsible for the formation of the pitted cones and mounds remains uncertain. Although this study does not claim to identify a specific process, we do suggest that geothermal activity is unlikely. No igneous volcanic edifice exists in proximity to the sedimentary volcanoes and we do not observe evidence of hydrothermal processes such as found elsewhere at Mars based on the morphology, mineral makeup, and precise composition of the HySi. Further studies, including terrestrial analogue field investigations, will be required to more accurately identify the geological processes responsible for the fluid overpressure and subsequent mobilization of volatile-bearing sediments. Contenders include rapid and sudden sedimentation, long-term load and subsidence, seismic shaking (including impact-induced marsquakes), tectonic shortening (i.e., fractures/faults formation, possibly induced by large-scale sediment compaction), mineral phase changes, permafrost development/destabilization and/or (peri)glacial processes, among others²⁵,²⁷,²⁹,³¹⁻³³,⁴²,⁵⁶,⁶⁹,⁸²⁻⁸⁸.

## Model age measurements suggest ancient sediments in young structures

Crater count-based dating of the Acidalia's TT (see Methods, Fig. 10 and Supplementary Text 2,6) indicate an Early-Amazonian age (2.3 + / -0.3 Ga), similar to what was previously proposed³³. For Utopia, we found similar ages (2.2 + / -0.5 Ga), consistent with the Early Amazonian period. While TT are Amazonian in age, the surrounding VBF terrains are dated back to the Early Hesperian period²⁰. There is a correlation between observed structures, their potential ages of formation, and the hydrated phases extruded by sedimentary volcanism. Indeed, the HySi-bearing cones are related to shallow reservoirs (<100 m) and are mostly associated with the youngest (Early Amazonian) TT. It is important to note that the depths that are suggested here represent first-order minimal depths. Thus, it is possible that even deeper sources are involved⁸⁵, which would then indicate access of even older materials and sediments in these sedimentary volcanoes. Notably, model ages for PHS-rich mounds are Early-Amazonian, but extraction depths indicate that they are able to sample deeply buried and therefore significantly older sediments. This opens the possibility that the extruded PHS-rich material may be relics of old evaporitic sediments that were formed when the VBF itself formed during the Hesperian period.

## Conclusions

The sites reported here exhibit similar morphological and mineralogical characteristics indicating shared geological processes that have long been proposed as being indicative of sedimentary volcanism¹⁸,¹⁹,²⁶,²⁹,⁵⁶,⁷⁴,⁸²,⁸⁸⁻⁹³. This study presents the first evidence for the presence of hydrated phases, namely hydrated silica and sulfates, in association with pitted cones and mounds in the NPs, confirming the sedimentary volcanism origin for these structures. The ages of these landforms imply that Early Amazonian Mars allowed conditions for fluids to reach the surface and flow to some limited spatial and temporal extents. In addition, we demonstrate the existence of buried aqueous reservoirs of both siliceous- and sulfate-rich materials. These were present in the NPs by the Amazonian and Hesperian periods, respectively.

While our study focused on the NPs, we did also look at other geological edifices in other lowlands (including pitted cones) that have been proposed to be Hesperian- and Amazonian-age sedimentary volcanoes. These are located in Chryse Planitia⁹⁴,⁹⁵ (19°8′N; 37°4′W) and Hydraotes Chaos⁸⁷ (0°13′N; 33°49′W). In both cases, the pitted cones exhibit similar HySi detections (Supplementary Fig. 3). This strongly suggests that, in the
same manner, sedimentary volcanism existed even more pervasively during Late Mars (see Supplementary Text 4,5 and Supplementary Data 1,2,4 for details and data).

Our findings may open up new perspectives for future Mars science and exploration missions. Exploring these relatively accessible sediments will enable access to aqueous subsurface reservoirs of the NPs that may resolve the debate about the presence of putative buried ocean-related sediments. This would also provide inputs on climate modelling to understand fluid stability in Late Martian history and to better characterize the nature of these subsurface fluids⁹⁵.

The presence of HySi-rich deposits in such contexts is of major astrobiological relevance. The buried sediments were protected from solar and cosmic radiation for most of Mars' history⁹⁶,⁹⁷. The oldest terrestrial biosignatures have been observed in HySi phases, testifying to silica's great capacity to protect biomolecules over geological time scales³⁷⁻¹⁰. Martian HySi-bearing sedimentary volcanoes therefore represent a double benefit for past water and astrobiological studies.

# Methods

## Mineral identifications at Mars

The primary data source for the Mars mineral detections is from the CRISM instrument onboard MRO³⁵. We processed quasi-nadir CRISM (onboard MRO) TRDR “targeted” observations, with observing modes “FRT”, “HRL”, “FRS” and “HRS” as described in Murchie et al. (2007)³⁵ and on the CRISM website (http://crism.jhuapl.edu/data/publicData.php). These correspond to small areas of Mars (less than 200 km²) mapped at better than 40 m/pixel spatial sampling, and with spectral sampling around 6.56 nm in the NIR range used in this study (1.0–2.6 µm). CRISM also comprises a visible-near infrared “S” channel which was also processed at each location of the Northern Plains (NP) where alteration minerals were found, to search for spectral counterparts in the visible range spectrum.

Lower spatial and spectral resolution “multispectral” CRISM nadir infrared data were occasionally used to search for mineralogy in the largest structures of interest (using observing modes “MSP” and “HSP”), but yielded no additional detections and so were not reported in this study. OMEGA data from Mars Express was also used at its highest achievable spatial resolution, which did not contribute additional detections.

We processed a large fraction of the available CRISM infrared TRDR in the NP. The targeted nature of the CRISM observations does not preclude bias in the sample selection because the NP of Mars are not contiguously covered by CRISM, and certain landforms were likely preferentially targeted. However, over the 100 s of observations analysed, the full range of longitudes and latitudes were investigated, as well as many recognized geological units and landforms, mitigating that bias. It does however imply that the altered landforms reported here are likely many orders of magnitude more common on Mars than detected currently, as they were not mapped with (good quality) CRISM data. We do not report any spectral counterpart in the visible channel of CRISM which correlates uniquely with the alteration signatures reported in the near-infrared channel. In particular, we searched for the crystalline hematite absorption band near 0.88 µm but found none in our detection dataset.

Data processing of the TRDR data follows similar steps as described in Carter et al. (2013)¹⁰. CRISM I/F data was retrieved through the ASU-hosted CRISM portal, then processed to reflectance, by accounting for the incidence angle and atmospheric absorptions using the “volcano-scan” method of Langevin et al. (2005)¹⁰. Our custom data reduction pipeline produces a “flat” spectral cube wherein the neutral mineralogy of the whole cube is assessed and removed at each pixel by a spectral division. The process is described in Torres et al. (2024)¹⁰. The mineral absorption bands are detected both using traditional band ratios and by measuring the spectral angles induced by the bands. Combination of spectral maps are made in order to extract more reliable and specific mineral detections, which produces the mineral maps of this paper, through a process described in Carter et al. (2023)¹² which allows extracting average spectra for each spatially

correlated cluster of detection, so-called “ROI spectra”. These are then compared to laboratory spectra of alteration minerals.

## Terrestrial opaline silica reference samples

To better characterise opaline silica CRISM detections, we compared the extracted spectra with different terrestrial reference samples (terrestrial analogues spectra are available in Supplementary Data 3). We selected near infrared spectra from various studies⁴⁴⁻⁴⁷,¹⁰⁷,¹⁰⁸. The samples were classified according to the type of silica (volcanic glasses, opal-A, opal-CT, chalcedony) and their geological origin (low-temperature surface alteration or continental weathering, high-temperature hydrothermal activity, high-temperature volcanic activity, unknown or uncertain geological origin). Some samples were in the form of powders, others were in the form of polished sections/chips. Depending on the studies, spectra were acquired under terrestrial ambient atmospheric conditions (20–22 °C, 1 bar), or in Mars-relevant atmospheric conditions. Low-pressure experiments were conducted at 20 °C and 1–7 mbar to simulate non-systematic dehydration of silica at the surface of Mars. Low-temperature experiments were conducted at –90 to –50 °C at 1 bar to observe the signature of frozen opals (when structural water molecules turn into ice in cryogenic conditions). We also selected some spectra acquired at very low atmospheric pressure (22 °C; 0.016 mbar) to simulate extreme non-systematic dehydration of silica. The list of all terrestrial samples used as references is available in Supplementary Data 3, where the data are classified according to acquisition procedures and presented along with the calculated values of the various spectral criteria presented below.

## Processing of near infrared spectra for HySi specie identification

Since terrestrial data were not acquired using the same instruments, and therefore not at the same spectral resolutions, all the terrestrial spectra have been degraded to the spectral resolution of the CRISM instrument (≈ 6.56 nm). Then, Martian CRISM data and terrestrial reference spectra were all processed in the same way before any calculation of spectral criteria. First, all spectra were smooth using the Savitzky-Golay method¹⁰⁹,¹¹⁰. Least square polynomial regression of adjacent points was conducted with 3rd-degree polynomial functions and a moving average window of about 7 to 9 points/spectels, up to 12 in rare cases.

After smoothing, the three absorption bands of silica at 1.4, 1.9 and 2.2 microns were isolated from the smoothed spectra using two anchor points for each and fitted using two gaussian functions related to A-type or B-type of water in hydrated silica⁴⁴,⁴⁶,¹⁰⁷,¹¹¹. The anchor points used to truncate each absorption are the following: 1.315 and 1.605 µm for the 1.4 µm band, 1.815 µm and 2.132 µm for the 1.9 µm band, and 2.125 and 2.370 for the 2.2 µm band. To minimise the influence of spectral noise, instrumental artefacts and spike generated by the atmospheric correction in CRISM data, and continuum variations, Gaussian modelling was assisted by manual continuum adjustments, adding anchor points when necessary. Anchor points were added without modifying the shapes and areas of absorption bands.

Each processing step (e.g., smoothing, then modelling) has been tested multiple times by slightly modifying the parameters, while manually checking the obtained results. We found that the processing parameters described above give the best results without significantly and unrealistically modifying the spectra: band shapes, inflection points, local band minima were kept while maintaining a good signal-to-noise ratio, especially for CRISM data. In most cases, and regardless of the chosen parameters, the spectral results were always very close to each other.

## Spectral criteria calculations

**Band minima positions (minimum of reflectance).** The band minima position is useful in defining the type of silica, (de)hydration behaviour, or state of pore water⁴⁴,⁴⁶,¹⁰⁷,¹⁰⁸,¹¹². The more the minimum is shifted at high wavelengths, the more crystalline the silica (opal-CT, chalcedony). Conversely, amorphous silica phases tend to be identified with minima at low wavelengths (opal-A, volcanic glasses). Shifts of the band minima
position are also helpful for tracing any silica dehydration (shifts at lower wavelengths) or crystallisation of ice inside the silica porosity (shifts at higher wavelengths due to water ice signatures). Minimum search was performed over large ranges for the 1.4 and 1.9 µm absorption band to account for possible large shifts due to the presence of ice bands in possibly “frozen silica”¹⁰⁸. Ranges are the following: from 1.34 µm to 1.58 µm for the 1.4 absorption and 1.87 µm to 2.05 µm for the 1.9 band.

Diagrams combining band minima positions of the 1.4 and 1.9 bands are available for terrestrial reference data in Supplementary Text 3. The fields are taken from previous studies⁴⁴,⁴⁶,⁴⁷, refined with the present dataset. Results for CRISM data for the different geomorphological classes and prospected regions are presented in Supplementary Text 4.

**Concavity-Ratio-Criterion (CRC).** Concavity-Ratio-Criterion (CRC) quantifies the shape of the high-wavelength side of the 1.4 and 1.9 absorption bands. This spectral parameter is useful to discern geological origins of opals regardless of their crystallinity. According to previous works⁴⁴,⁴⁶,⁴⁷, high CRC values indicate opals formed by medium-to-high temperature hydrothermal activity (T > 60 °C) whereas low values are mostly indicative of opals formed by low-temperature hydrothermal activity or continental surface alteration (T < 60 °C).

For the 1.4 µm absorption, we chose two anchor points at $λ_S ≈ 1.34$ µm and $λ_L ≈ 1.58$ µm. Then, two band depths were calculated: $BD_C$, the real band depth of the inflection point at ≈ 1.46 µm, and $BD_C^*$, the virtual band depth of the same inflection point using a linear continuum between the band minimum and the anchor point $λ_L$.

CRC_C is calculated as follows:

$$CRC_C = \frac{BD_C}{BD_C^*}$$

The same calculation was applied for the 1.9 absorption, using anchors at $λ_S ≈ 1.84$ µm and $λ_L ≈ 2.11$ µm, and an inflection point at ≈ 1.96 µm.

Error in the CRC calculation was calculated empirically by shifting the two anchor points $λ_S$ and $λ_L$ over +/−9 nm (a range of 18 nm, 6 to 7 spectels). This generates 126 distinct combinations for a single measurement. The CRC was calculated for each combination. The retained value for the CRC is the average of all calculated values, and the error represents the standard deviation (1σ).

The obtained CRC values for terrestrial reference data can be combined with the band minima positions (MIN1.4 vs. CRC1.4 or MIN1.9 vs. CRC1.9) or between them (CRC1.4 vs. CRC1.9). The first combinations are useful to decipher between silica phases using band minima positions and geological origins using CRC values. The second combination is useful to assess geological origins with higher certainties. Note that in both cases, these diagrams can be helpful to determine putative occurrence of dehydrated silica or frozen silica⁴⁶,¹⁰⁸. The obtained diagrams for terrestrial reference data are available in Supplementary Text 3. The various fields defined by previous works⁴⁴,⁴⁶,⁴⁷ were refined in the light of the present dataset. The results for CRISM data for the different geomorphological classes and prospected regions are presented in Supplementary Text 4.

**Relative area of absorption bands.** The area of each absorption band was calculated as the sum of the two gaussian functions used for the fitting process. These areas were then converted into relative areas where the area of a single band is normalised to the sum of all band areas. Relative area contributions were then given in percent. These relative area values were used in the classification of silica-rich materials from Pineau et al. (2020)⁴⁶, which is in the form of a ternary diagram, refined with the present dataset. The various fields obtained using terrestrial reference data are shown in Supplementary Text 3, and the results for CRISM data for the different geomorphological classes and prospected regions are presented in Supplementary Text 4. Note that this diagram is only helpful to decipher silica phases and degree of (de)hydration. No information on

geological origin can be obtained here (except for volcanic glasses that are indicative of volcanic activity at first glance).

**Surface grain size estimates**

We have estimated possible particle size of extruded materials and surrounding embedding units in order to provide lithological constraints on these two. Particle size was estimated from empirical laws and thermal inertia (TI) observations following the method provided by Presley & Christensen (1997)¹¹³. The reasoning and procedure we used is detailed in Supplementary Text 2. The TI of the different surfaces of interest were extracted from TI maps generated from THEMIS data by the Thermo-physical Analysis Tools for Mars Research (MARSTHERM, https://marstherm.psi.edu/) developed by the Planetary Science Institute in Tucson, Arizona, and other institutions¹¹⁴. Several dozen maps have been requested for different areas in Acidalia and Utopia Planitiae, where we detect mineral phases associated with sedimentary volcanism. For each mapped zone, TI are extracted from tables and presented as a +/− symmetrical normal distribution. Three TI values are calculated: an average TI, as well as minimum and maximum values (average +/− 2σ). These values are then injected into the equations provided in Presley & Christensen (1997)¹¹³ to calculate a grain size range (from minimum and maximum TI) and a central mean grain size. TI values and calculated grain sizes are synthesized in Supplementary Data 2.

**Estimating sources depths using a classical Buoyancy model**

In order to obtain information on the units' stratigraphy where hydrated phases were extruded by sedimentary volcanism, we estimated possible depths of the subsurface sources in the Acidalia TT, and in the -presumably-VBF terrains over Utopia Planitia. These depths were calculated using a conventional buoyancy model commonly used in the case of sedimentary volcanism. According to previous studies⁶⁷,⁶⁸,¹¹⁵, source depth D (in metres) is expressed as:

$$D = \frac{H(\rho_m - \rho_{atm})}{(\rho_s - \rho_m)}$$

where: H is the cone/mound height calculated in the ArcGIS software from Digital Elevation Models (DEM) that were generated by MarsSI¹¹⁶,¹¹⁷ (marssi.univ-lyon1.fr), $ρ_m$ is the density of extruded/ejected materials, $ρ_s$ is the density of overlying materials/surrounding plains, and $ρ_{atm}$ is the density of the present Martian atmosphere (fixed at 0.02 kg.m⁻³). Many different $ρ_m$ and $ρ_s$ were tested (see Supplementary Text 2). We also studied the case of sedimentary volcanism taking place in an aqueous medium rather than in a Martian atmosphere; then $ρ_{atm}$ must be changed into $ρ_{water} = 1000$ kg.m⁻³.

All possible results are displayed as synthetic tables that are detailed and discussed in Supplementary Text 5. Full results are provided in Supplementary Data 4.

**Surface model age measurements**

To check whether the sedimentary volcanism events investigated in this study occurred at the same periods on Acidalia and Utopia Planitiae, we carried out crater-count model age dating. We identify the regional units associated with the hydrated minerals local detections presented in this study using THEMIS day/night observations³⁹ and refined crater count areas using CTX V01 mosaics¹¹⁸ [NASA/PL/MSSS/The Murray Lab; https://murray-lab.caltech.edu/CTX/]. We derived their model age as “closest putative age” of sedimentary volcanism and formation of hydrated phases presented in this study. Given that the hydrated phases are observed in these cones/mounds, their exhumation is synchronous with the TT’ sedimentary volcanism. Under the assumption that these phases were therefore present within the TT’ stratigraphy, they predate sedimentary volcanism events and have an age comparable to the deposition age of the TT. It is possible that the massive activity of sedimentary volcanism, aeolian erosion and/or sedimentation may have erased traces of meteoritic impacts since the TT were deposited. Thus, the calculated ages represent a “retention
age”, at best slightly posterior to the initial TT’s deposition, and anterior to the sedimentary volcanic events that extruded the hydrated phases. Further information on how the surfaces have been mapped are provided in Supplementary Text 2.

Areas are too small (<50,000 km²) to have retained enough kilometric craters, thus preventing the use of manual crater databases¹¹⁹,¹²⁰ for age-dating¹²¹. The presence of too many circular structures (i.e., pitted cones and mounds) prevents the use of automatic crater mapping method¹²²⁻¹²⁵ for model age derivation. Moreover, units located in Acidalia Planitia are contaminated by secondary crater clusters originating from Mojave crater¹²⁴. For these reasons, impact craters superimposed on, or whose ejecta overlap the various units, were manually mapped using the “CraterTools” add-on implemented in the ArcGIS software¹²⁶. Crater counts were then processed into the CraterStatsII software¹²⁷, where the crater size-frequency distributions (Crater SFD) were displayed in differential form and fitted with a production function from the Hartmann (2005)'s chronology system¹²⁸ using the Poisson timing analysis method¹²⁹. Crater SFDs, and results summarized in Supplementary Text 6, show a relatively good alignment with a production function (PF) for craters as small as 400-700 metres, with no correlation between the minimum diameter used to fit a PF with the crater data and obtained model ages. No areas smaller than 1000 km² were used to derive model ages as advocated by Warner et al. (2015)¹²¹. Model Age Derivation results are detailed in Supplementary Text 6.

## Data availability

All data used for this work are publicly available. CRISM data can be downloaded from NASA's Planetary Data System (PDS) (https://pds-geosciences.wustl.edu/missions/mro/crism.htm) or on the CRISM website (http://crism.jhuapl.edu/data/publicData.php). The method used to process CRISM data are described in the Method section and follow the same procedures as Carter et al. (2013)¹⁰⁴. The mineralogical survey at a global scale discussed in this study was explained in Carter et al. (2023)¹² and mineralogical maps, available as GIS-raster files, can be downloaded from the MOCAAS project website (https://www.ias.u-psud.fr/moccas/). All HiRISE images analysed in this study are publicly available from NASA/JPL/University of Arizona: https://www.uahirise.org/. The CTX V01 mosaics¹¹⁸ are publicly available from NASA/JPL/MSSS/The Murray Lab: https://murray-lab.caltech.edu/CTX/. HiRISE and CTX Digital Elevation Models (DEM) were generated and downloaded from MarsSI¹⁶,¹¹⁷ (mars-si.univ-lyon1.fr). CaSSIS images are publicly available at https://observations.cassis.unibe.ch/. THEMIS data were downloaded using the NASA's PDS. Thermal inertia maps derived from the THEMIS data were compiled and downloaded from the Thermophysical Analysis Tools for Mars Research (MARSTHERM, https://marstherm.psi.edu/) developed by the Planetary Science Institute in Tucson, Arizona, and other institutions¹¹⁴. CRISM and THEMIS Images IDs are provided in the Supplementary Data 1 and 2 respectively. Spectra of the terrestrial reference samples, compiled from different published works⁴⁵⁻⁴⁷,¹⁰⁸, are available in the Supplementary Data 3. The data that support the findings of this study are available from the corresponding author, M.P., upon reasonable request.

Received: 24 February 2025; Accepted: 18 August 2025;
Published online: 09 October 2025

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## Acknowledgements

This work was supported by the Agence Nationale de la Recherche (ANR, France) under the contract ANR-20-CE49-0013 entitled Paleosilica (https://paleosilica.lam.fr/), the Centre National de la Recherche Scientifique (CNRS, France), the Centre National d'Études Spatiales (CNES, France) through the Programme National de Planétologie. Authors also received support from the French government under the France 2030 investment plan, as part of the Initiative d'Excellence d'Aix-Marseille Université - A*MIDEX AMX-21-RID-O47. This work has also received support from the ERC OCEANID project (Grant agreement ID: 101045260; doi: 10.3030/101045260, https://cordis.europa.eu/project/id/101045260) funded by the Horizon programme from the European Research Council. We also like to thank Cédric Millot (Laboratoire de Géologie de Lyon, France) for useful discussion about formation and associated processes of small impact craters on Mars. Authors would also like to greatly thank Frances Westall (Centre de Biophysique Moléculaire, Orléans, France) and Simon Gouzy (Laboratoire de Planétologie et Géosciences, LPG, Nantes, France) for providing meaningful information about organic matter and biosignatures preservation in silica-rich phases. The authors wish to express their thanks and gratitude to the two reviewers, one anonymous and William Farrand, whose suggestions and pertinent comments greatly improved the quality of the article.

## Author contributions

The conceptualization of this study has been led by M.P. and J.C who both performed CRISM data collection and analysis. These Martian spectral data were compared to terrestrial analogues for which references data collection and analysis has been conducted by M.P. Geomorphological analysis and cartography of the Martian landforms discussed in this study have been performed by M.P., J.C., A.L., N.M, and L.L.D. Crater Count Dating has been conducted by A.L. and M.P. Source depths calculations of the sediments extruded by sedimentary volcanism have been performed by M.P. Main contributors for discussing sedimentary volcanism processes and their implications at Mars are M.P., E.R. and A.Z. Discussions about Martian subsurface and surface aqueous geology arise from the Mars geology expertise of M.P., J.C., A.L., N.M., L.L.D. and C.Q.N. First author M.P. led the writing of the manuscript with all authors providing critical comments and contributing to the discussion of the study. The figures and artwork were completed by M.P., J.C., A.L. and E.R.

## Competing interests

The authors declare no competing interests.

## Additional information

**Supplementary information** The online version contains supplementary material available at https://doi.org/10.1038/s43247-025-02713-3.

**Correspondence** and requests for materials should be addressed to M. Pineau.

**Peer review information** *Communications Earth & Environment* thanks William Farrand and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: Brittany Cymes and Joe Aslin. A peer review file is available.

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