• Aram Dorsum: An Extensive Mid‐Noachian Age Fluvial Depositional System in Arabia Terra, Mars

      Balme, MR; Gupta, S; Davis, Joel; Fawdon, P; M. Grindrod, P; Bridges, JC; Sefton‐Nash, E; Williams, RME (American Geophysical Union (AGU), 2020-04-15)
      A major debate in Mars science is the nature of the early Mars climate, and the availability ofprecipitation and runoff. Observations of relict erosional valley networks have been proposed as evidencefor extensive surface runoff around the Noachian‐Hesperian boundary. However, these valley networks onlyprovide a time‐integrated record of landscape evolution, and thus, the timing, relative timescales andintensity of aqueous activity required to erode the valleys remain unknown. Here, we investigate an ancientfluvial sedimentary system in western Arabia Terra, now preserved in positive relief. This ridge, “AramDorsum,” is flat‐topped, branching, ~85 km long, and particularly well preserved. We show that AramDorsum was an aggradational alluvial system and that the existing ridge was once a large river channel beltset in extensive flood plains, many of which are still preserved. Smaller, palaeochannel belts feed themain system; their setting and network pattern suggest a distributed source of water. The alluvial successionis up to 60 m thick, suggesting a formation time of 105to 107years by analogy to Earth. Our observationsare consistent with Aram Dorsum having formed by long‐lived flows of water, sourced both locally, andregionally as part of a wider alluvial system in Arabia Terra. This suggests frequent or seasonal precipitationas the source of water. Correlating our observations with previous regional‐scale mapping shows thatAram Dorsum formed in the mid‐Noachian. Aram Dorsum is one of the oldest fluvial systems described onMars and indicates climatic conditions that sustained surface river flows on early Mars.
    • A Diverse Array of Fluvial Depositional Systems in Arabia Terra: Evidence for mid-Noachian to Early Hesperian Rivers on Mars

      Davis, Joel; Gupta, S; Balme, M; M. Grindrod, P; Fawdon, P; Dickeson, ZI; Williams, RME (Wiley, 2019-07-22)
      Branching to sinuous ridges systems, hundreds of kilometers in length and comprising layered strata, are present across much of Arabia Terra, Mars. These ridges are interpreted as depositional fluvial channels, now preserved as inverted topography. Here we use high‐resolution image and topographic data sets to investigate the morphology of these depositional systems and show key examples of their relationships to associated fluvial landforms. The inverted channel systems likely comprise indurated conglomerate, sandstone, and mudstone bodies, which form a multistory channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, which we interpret as paleolake deposits. Some inverted channels are located within erosional valley networks, which have regional and local catchments. Inverted channels are typically found in downslope sections of valley networks, sometimes at the margins of basins, and numerous different transition morphologies are observed. These relationships indicate a complex history of erosion and deposition, possibly controlled by changes in water or sediment flux, or base‐level variation. Other inverted channel systems have no clear preserved catchment, likely lost due to regional resurfacing of upland areas. Sediment may have been transported through Arabia Terra toward the dichotomy and stored in local and regional‐scale basins. Regional stratigraphic relations suggest these systems were active between the mid‐Noachian and early Hesperian. The morphology of these systems is supportive of an early Mars climate, which was characterized by prolonged precipitation and runoff.
    • Episodic and Declining Fluvial Processes in Southwest Melas Chasma, Valles Marineris, Mars

      Davis, J; M. Grindrod, P; Fawdon, P; Williams, R; Gupta, S; Balme, M (American Geophysical Union, 2018-08-29)
    • Glacial and gully erosion on Mars: A terrestrial perspective

      Conway, SJ; Butcher, FE; de Haas, T; Deijns, AA; M. Grindrod, P; Davis, JM (Elsevier, 2018-05-24)
      The mid- to high latitudes of Mars host assemblages of landforms consistent with a receding glacial landscape on Earth. These landforms are postulated to have formed >5 Ma under a different climate regime when Mars' orbital obliquity was on average 10° higher than today. Here, we investigate the spatiotemporal relationship between gullies and glacial landforms, both common in the mid-latitudes. Gullies are kilometre-scale landforms with a source alcove, transportation channel, and depositional apron. The glacial landforms comprise (1) extant viscous flow features (VFF) that extend from the base of crater walls into the interior of crater floors and are widely interpreted as debris-covered glaciers containing extant ice, and (2) landforms such as arcuate ridges at the base of crater walls that have been interpreted as relicts of more recent, less extensive glacial advances focussed on crater walls. We measure headwall retreat associated with glacial landforms and date their host-craters to constrain minimum headwall retreat rates. We record headwall retreat rates up to ~102 m My−1 for the youngest suite of glacial landforms, equivalent to erosion rates of wet-based glaciers on Earth and to headwall retreat rates associated with martian bedrock gully systems. We find extensive evidence for a single erosional episode dating 5–10 Ma, which postdates emplacement of the majority of VFF but seems to predate formation of the gullies. We propose that the wet-based glacial episode was associated with glaciation focussed on the crater walls rather than melting of the glacial ice deposits on the crater floors (VFF). This is consistent with our observations of crater wall morphologies, including the presence of arcuate ridges consistent with terrestrial glaciotectonic features that require liquid water to form, textural alteration of the eroded bedrock surface consistent with ice-segregation and frost-shattering, and the presence of downslope pasted-on terrain, tentatively interpreted here as glacial till deposits sourced from glacial erosion of the crater wall. The pasted-on terrain is usually interpreted as a thicker, latitude-dependant mantle located on sloping terrain formed from airfall of ice nucleated on dust, but we suggest that it has been reworked by glaciation and is predominantly glacial in origin. Although our results cannot substantiate that gullies are produced by meltwater, the discovery of this wet glacial event does provide evidence for widespread meltwater generation in Mars' recent history.
    • Morphology, Development, and Sediment Dynamics of Elongating Linear Dunes on Mars

      Davis, Joel; Banham, Steven; M. Grindrod, P; Boazman, Sarah; Balme, Matthew; Bristow, Charlie (American Geophysical Union (AGU), 2020-05-24)
      Linear dunes occur on planetary surfaces, including Earth, Mars, and Titan, yet their dynamics are poorly understood. Recent studies of terrestrial linear dunes suggest they migrate by elongation only in supply‐limited environments. Here, we investigate elongating linear dunes in the Hellespontus Montes region of Mars which are morphologically similar to terrestrial systems. Multitemporal, high‐resolution orbital images show these linear dunes migrate by elongation only and that the fixed sediment source of the dunes probably restricts any lateral migration. Some linear dunes maintain their along‐length volume and elongate at rates comparable to adjacent barchans, whereas those which decrease in volume show no elongation, suggesting they are near steady state, matching morphometric predictions. Limited sediment supply may restrict Martian linear dunes to several kilometers, significantly shorter than many terrestrial linear dunes. Our results demonstrate the close similarities in dune dynamics across the two planetary surfaces.
    • Quantified Aeolian Dune Changes on Mars Derived From Repeat Context Camera Images

      Davis, Joel; M. Grindrod, P; Boazman, Sarah; Vermeesch, P; Baird, T (American Geophysical Union (AGU), 2019-12-11)
      Aeolian systems are active across much of the surface of Mars and quantifying the activity of bedforms is important for understanding the modern and recent Martian environment. Recently, the migration rates and sand fluxes of dunes and ripples have been precisely measured using repeat High Resolution Imaging Science Experiment (HiRISE) images. However, the limited areal extent of HiRISE coverage means that only a small area can be targeted for repeat coverage. Context Camera (CTX) images, although lower in spatial resolution, have wider spatial coverage, meaning that dune migration can potentially be monitored over larger areas. We used time series, coregistered CTX images and digital elevation models to measure dune migration rates and sand fluxes at six sites: Nili Patera, Meroe Patera, two sites at Herschel crater, McLaughlin crater, and Hellespontus Montes. We observed dune displacement in the CTX images over long‐term baselines (7.5–11 Earth years; 4–6 Mars years). Bedform activity has previously been measured at all these sites using HiRISE, which we used to validate our results. Our dune migration rates (0.2–1.1 m/EY) and sand fluxes (2.4–11.6 m3 m−1 EY−1) compare well to measurements made with HiRISE. The use of CTX in monitoring dune migration has advantages (wider spatial coverage, faster processing time) and disadvantages (ripples not resolved, digital elevation model dune heights may be underestimates); the future combined use of HiRISE and CTX is likely to be beneficial.
    • Stepped fans and facies-equivalent phyllosilicates in Coprates Catena, Mars

      M. Grindrod, P; Warner, NH; Hobley, DEJ; Schwartz, C; Gupta, S (2017-10-28)