Figure 3 - available via license: Creative Commons Attribution 4.0 International
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Perspective view of the alcove-ridge system in crater B (top) compared to the upslope-facing scarps and concentric crater fill in a recently glaciated Amazonian-aged crater in Newton basin (bottom; e.g., Head et al. 2008; Jawin et al. 2018). Upslope-facing scarps in Amazonian-aged craters represent margins of entrained debris shed by ablating cold-based glacial lobes. Distribution of the proximal ridges in crater B closely matches that of crater wall alcoves and upslope-facing scarps, suggestive of a similar cold-based glacial origin in the Noachian. A ∼15 km horizontal field of view (FOV) with 4× vertical exaggeration (top); ∼5 km horizontal FOV with 2× vertical exaggeration (bottom).
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A body of geologic evidence suggests that Noachian-aged craters on Mars were modified primarily by runoff from rainfall in a warm and wet early Mars climate. Although melting and runoff of frozen water ice have been suggested as plausible alternatives, supporting geomorphic evidence of Noachian glaciation on Mars has been elusive. We previously ide...
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... B, the first CSDB crater we characterized, is located at 20.3° S, 42.6° E and has a diameter of 54 km (Figures 1-3). Perspective view of the alcove-ridge system in crater B (top) compared to the upslope-facing scarps and concentric crater fill in a recently glaciated Amazonian-aged crater in Newton basin (bottom; e.g., Head et al. 2008;Jawin et al. 2018). ...
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... crater B, the scarps and alcoves associated with the abrupt initiation of tributary sinuous ridges (Figures 1-3) led us to hypothesize that the ridges had formed as proglacial outwash channels downslope of a glacial margin during a Noachian paraglacial phase ). One notable difference was the lack of preserved concentric crater fill (CCF) in the floor of crater B, which is a hallmark of Amazonian intracrater glaciation (e.g., Levy et al. 2010;Dickson et al. 2012;Fastook & Head 2014). ...
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... the melting evidenced by the large inverted fluvial channel networks and paleolake basins within crater B (Figures 1-3) suggests a more extensive paraglacial episode without CCF preservation than is known from the Amazonian. This model of Noachian cold-based glacial melting and removal in crater B can therefore be used to search for other instances of Noachian cold-based crater wall glaciation and proglacial fluvio-lacustrine activity. ...
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... to the south, two sinuous ridge networks are stacked on top of one another (Figure 13), a configuration that we did not previously observe in crater B (Boatwright & Head 2021). ...
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... lower ridges have a simple scarp planform, while the higher ridge has a complex scarp planform. The stratigraphic-planform coupling observed here is consistent with the stacked ridges observed elsewhere in the crater ( Figure 13). A third type of ridge in the chaotic terrain forms pit boundaries with steeper sides facing inward toward pit floors; these typically have a sinuosity index (SI) of 1.4 (Figure 16), which is higher than that of the tributary ridges we have hitherto characterized as "sinuous" (SI 1.1). ...
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Citations
The evolution of the climate and hydrochemistry of Mars is still a mystery but it must have been at least occasionally warm and wet to have formed the ancient fluvial and lacustrine landforms observed today. Terrestrial examples and geochemical modeling under proposed early Mars conditions show that zeolite minerals are likely to have formed under alkaline (pH > 8) conditions with low water/rock ratio and surface temperatures below 150°C. The identification and spatial association of zeolites on the surface of Mars could thus be used to reconstruct the paleoclimate, paleohydrochemistry, and geological evolution of some locations on Mars. Previous studies identified the zeolite analcime and discuss the difficulties of identifying other zeolite species on the surface of Mars using orbital spectroscopy. We used published global mineralogical, geological, geomorphological, hydrological, physical, and elemental abundance maps and the locations of hydrous minerals detected and mapped using orbital data to create a map that delineates favorable areas to look for zeolites on Mars. We used the data‐driven fuzzy‐based Weights‐of‐Evidence method to identify and map favorable areas for zeolites on the surface of Mars up to ±40° latitude toward the poles. The final map shows that the eastern and western Arabia deposits, some sites in the Medusae Fossae formation, and some areas within and near Valles Marineris, Mawrth Vallis, highlands north of Hellas, and the Terra Cimmeria and Terra Sirenum regions would be favorable areas to look for zeolites using targeted orbital spectral analysis or future in situ observations.
Long-standing paradigms of early Mars have posited that the ambient climate must have been temperate enough to support flowing liquid water at the surface for hundreds of millions of years. While runoff from rainfall is usually considered to be the most likely mechanism of fluvial erosion in the Noachian, the possibility remains that fluvial erosion could have occurred through the melting of snow or ice in a subfreezing ambient climate. We previously characterized two Noachian closed-source drainage basins, or CSDBs, in the Terra Sabaea region of the southern highlands. These CSDBs displayed evidence for glacial melting in crater interiors that led to hydrologically isolated fluvial and lacustrine activity in crater floors, which is distinct from previously identified crater basin lakes on Mars that have primarily external drainage sources. Here, we describe the results of a survey across a ∼800,000 km² region of Terra Sabaea in which we searched for similar geomorphic signals of ancient glaciation in the southern highlands. We identified 42 inverted fluvial channel networks occurring within crater floors and enclosed topographic basins whose formation is consistent with runoff derived from top-down glacial melting. The altitude distribution of host crater rim crests (+1.1 to +3.3 km) indicates the potential for proglacial fluvial and lacustrine activity in these locations that is consistent with evolving glacial ice stability in the Late Noachian to Early Hesperian as predicted by climate models. We provide additional evidence that these features are likely to have formed in a “cold and icy” early Mars climate that was dominated by an adiabatic cooling effect and widespread glacial ice cover in the southern highlands.
Inverted fluvial channels are widespread on Mars, and along with valley networks, they provide evidence of flowing liquid water in the early period of the planet's geologic history. We previously described tributary ridge networks within a closed‐source drainage basin crater in the southern highlands, which we interpreted as inverted fluvial channels that were fed by meltwater from the surface of cold‐based glaciers located in crater wall alcoves. Here, we estimate both the paleodischarge within the inverted channels and the necessary melting rates for discharge sources in glacial alcoves. We find that paleodischarges of up to ∼7,000 m³/s were possible with melting rates exceeding 2,000 mm/hr in an extreme warming scenario, with lower rates potentially representing more gradual glacial ice loss. These end‐member estimates can provide key constraints for further early Mars climate and landform evolution modeling.
Pit-floored craters (PFCs) have been observed in the highlands surrounding the Hellas impact basin on Mars. The pits consist of large irregularly shaped depressions (∼10s of km wide and ∼100s of m deep), often with steep layered walls and terraced interiors. We analyze a previously recognized population of circum-Hellas PFCs and nearby layered terrains using high-resolution visible imagery and stereo topography data and compare them to current models of Noachian–Hesperian geologic and climatic evolution. We find little evidence for regionally integrated fluvial runoff or crater rim breaching; crater interiors instead display fine-scale layering potentially related to pyroclastic, aeolian, or glacial deposition. Steep pit scarps, terraced pit floors, and a lack of traditional sediment transport pathways implicate sublimation of ice and removal into the atmosphere as the major pit-forming process. Radiating ridges interpreted as inverted fluvial channels emanating from raised pit boundaries further suggest water ice as a dominant crater floor fill material. Latitudinal distinctions in PFC morphology and evidence for both recent and past crater mantling and degradation events suggest a climate-controlled origin and evolution of circum-Hellas layered terrains dominated by the emplacement and removal of snow and ice.
Hundreds of ancient lake basins detected on Mars via orbital remote sensing represent rare oases of hydrosphere–atmosphere–lithosphere interactions with great astrobiological potential. These palaeolake basins, and associated lacustrine deposits, could preserve evidence of biogenesis on Mars, and their geology, mineralogy and geochemistry place strong constraints on past climate. Most Martian palaeolakes date to the Noachian (>3.7 Gyr ago (Ga)) and probably lasted ~102–106 years, representing only a small fraction of the ~400 Myr of Noachian time. However, some palaeolakes occurred during the Hesperian (3–3.7 Ga), and it is likely that many shallow thermokarst lakes occurred in the Amazonian (<3 Ga) but left few traces. Noachian lacustrine deposits contain detrital Fe/Mg-rich clay minerals as well as authigenic Fe/Mg carbonates, sulfates, silica, chlorides and clay minerals that potentially preserve the characteristics of the ancient atmosphere and climate. While Martian palaeolakes are undeniably among the top targets for future surface exploration and sample return, many questions surrounding prospects for biogenesis and biological productivity in short-lived lakes and transient warm climates on an otherwise cold planet remain. Martian lakes also provide tremendous comparative value for reconstructing the geology and geobiology of inland waters on the Archaean Earth. Mars hosted hundreds of lakes, most of which formed earlier than 3.7 billion years ago and lasted only a limited amount of time. This overview of their characteristics and mineralogy highlights the importance of the Martian lakes as a record of ancient climate and potential for biogenesis.
