The subsurface as the key to surface on Martian gullies

Post by Dr. T. de Haas, Department of Geography, Durham University.

Martian gullies are composite landforms that comprise an alcove, channel and depositional fan. They are very young geological features, some of which have been active over the last million years. Water-free sediment flows, likely triggered by CO2 sublimation, debris flows, and fluvial flows have all been hypothesized to have formed gullies. These processes require very different amounts of liquid water, and therefore their relative contribution to gully-formation is of key importance for climatic inferences. Formative inferences based on surface morphology may be biased however, because of substantial post-depositional modification (Images 1-3).

Image1

Image 1: Morphometry, morphology and stratigraphy of depositional landforms in Galap crater. (a) Overview and digital elevation model of Galap crater. (b) Detail of northwestern slope showing gradients of catchment and depositional fan. (c) Detail of proximal fan surface. (d) Detail of distal fan surface. (e) Detail of fan surface with incised channels; the dashed line indicates the rockfall limit. (f) Example of stratigraphic section. (h) Same stratigraphic section as in f, but with optimized contrast in the section. Arrows denote downslope direction. HiRISE image PSP_003939_1420.

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Sedimentology and Hydrology of an Amazonian paleo-fluivo-lacustrine systems on Mars (Moa Valles)

Post contributed by Francesco Salese from IRSPS/Dipartimento INGEO, Università D’Annunzio, Pescara, Italy.

Mars, is one of the planetary bodies where water flowed and where it may transiently flow today under certain conditions. Many martian paleodrainage systems and well-preserved fluvial and lacustrine deposits have been recognized and studied in the last two decades (see further reading). Widespread dendritic valley networks and the presence of extensive fluvial features on ancient martian terrains suggest that a relatively “warm and wet” climate was prevalent early in the planet’s history (about 3.7 Ga). This is in stark contrast with the hyper-arid, extremely cold climate that is thought to have persisted from 3 Ga until the present (Amazonian Era). The subject of this post is Moa Valles [Salese et al., 2016], which is a 2 billion year old paleodrainage system (Figure 1) that is nearly 300 km long and is carved into ancient highland terrains of Tempe Terra in the northern hemisphere of Mars. Understanding the origin and evolution of this type of complex and interconnected paleo-fluvio-lacustrine system is critical for understanding the early martian climate.

Figure2

Figure 1: The upper panel shows the THEMIS-VIS daytime mosaic of Moa Vallis system.The lower panel is a line drawing showing the channel system in blue lines, red dotted lines represent wrinkle ridges, the drainage basin is delimited in grey, and fan-shaped and deltaic deposits in orange. The total mapped length of the channel as shown here is ~325 km, and the flow direction is towards the east.

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Experimental Delta Formation in Crater Lakes

Post by G. de Villiers, Faculty of Geoscience, Utrecht University.

Fan-shaped deposits have been identified on the surface of Mars (Image 1). These sediment bodies often occur within impact craters and, specifically in the cases of fan deltas, suggests that these craters were once lakes early in Martian history. Fan delta morphologies are indicative of upstream (e.g. flow discharge and sediment properties) and downstream (e.g. basin characteristics) parameters, from which the hydrological conditions at the time of formation can be inferred (e.g. Kleinhans et al. 2010).

IAGFigure1

Image 1: Examples of fan delta deposits on Mars, formed in enclosed impact crater or rift basins. A) Single-scarped, branched prograding delta (PSP_006954); B) Single-scarped, smooth prograding delta (I10805012); and C) Multiple-scarped, stepped retrograding delta (V17040003). White line is approximately 5 km.

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