44 research outputs found

    Amazonian-aged fluvial system and associated ice-related features in Terra Cimmeria, Mars

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    The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340 km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between ∼1.8+0.2 −0.2 Ga to 510+40 −40 Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events

    The Hypanis Valles delta: The last highstand of a sea on early Mars?

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    One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment (4.6 x 105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars

    Impact crater degradation, Oxia Planum, Mars

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    The main goal of the European Space Agency (ESA) and Roscosmos ExoMars rover mission is to collect samples from the near-subsurface of Mars. The rover will look for any physical or chemical evidence of ancient life in the near subsurface. This map shows the distribution of impact craters at this proposed landing site in Oxia Planum on Mars. The map records 1199 impact craters > 500 m in diameter in a 5.0° × 2.5° region around Oxia Planum. The impact craters are symbolised based on the way different aspects of their morphology have degraded since their formation. The distribution of degradation and burial morphologies of impact craters can be used to determine where burial and erosion processes have occurred. Because the formation of impact craters is well constrained, occurs instantly and with a predictable flux, future studies could use this knowledge and our dataset to constrain when these events occurred

    A Diverse Array of Fluvial Depositional Systems in Arabia Terra: Evidence for mid‐Noachian to Early Hesperian Rivers on Mars

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    Branching to sinuous ridges systems, 100s 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 datasets 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 multi‐storey channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, that 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 towards 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
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