Comparitive Study of the Geomorphological Characteristics of Valley Networks between Mars and the Qaidam Basin

The complex valley networks that cross the Martian surface offer geomorphologic evidence of the presence of liquid water at some point in its history. However, the derivation of both temporal and hydrological dimensions of this climate phase is far from settled. Studies comparing terrestrial fluvial networks of known formation environments with those on Mars can be used as a key to unlock the past. This work represents an analogy study and comparison between the river networks in the Qaidam Basin and those on Mars. As the Martian valley networks formed in different geologic periods with characteristic and unique features, three cases from the Noachian to the Amazonian were selected to be compared with streams in the Mangya area, where the climate is extremely arid. In terms of the maturity of the dendritic river system, shape, concave index, and branching angle (BA), the valley network in the Mangya area is comparable to Naktong Vallis, dated to the Hesperian. We also calculated throughout the valley networks on Mars the parameters of the BA and the concave index, both of which are important climatic indicators. The results show that the climate on Mars became progressively more arid, starting from the Noachian up to the Amazonian.

Inverted Fluvial Channels in Terra Sabaea, Mars: Geomorphic Evidence for Proglacial Lakes and Widespread Highlands Glaciation in the Late Noachian

<p>Most Noachian-aged craters on Mars have distinctive morphologic characteristics that suggest they were modified by runoff from rainfall in a predominantly warm and wet early Mars climate. However, melting and runoff of frozen water ice (snowmelt) represents a plausible alternative for fluvial erosion in the Noachian. In recent work, we described a "closed-source drainage basin" (CSDB) crater in Terra Sabaea that contained inverted fluvial channel networks and lacustrine deposits. The crater is not breached by fluvial channels and lacks depositional morphologies such as fans or deltas, which sets it apart from previously described open- and closed-basin lakes on Mars that are hydrologically connected to their surroundings. The lack of hydrologic connectivity, along with additional evidence of remnant cold-based glacial morphologies within the crater, led us to hypothesize top-down melting of a cold-based crater wall glacier as the source of runoff and sediment for the fluvial and lacustrine deposits, which produced one or more proglacial lakes within the crater.</p><p>Here, we describe the results of a follow-on survey of the region within 500 km of the first CSDB crater. We searched for examples of features that could be interpreted as inverted fluvial channels regardless of their location. Of the 42 inverted channel networks we identified, 19 are located within unbreached craters; 17 are within breached craters with at least one inlet but no outlets; and 6 are located in the intercrater plains. The features are not randomly distributed; rather, they form two distinct groupings, one in the southwest of the study area and another in the east, with very few in the north or west. All but one occurs within an elevation range of 0 to +3 km. There are several previously identified closed-basin lakes within the study area, but none contained inverted channels.</p><p><span>The 42 inverted channel systems represent a wide variety of geologic and hydrologic settings. The region has distinctly low valley network density, and the few mapped valley networks in the region are clustered around +2 km elevation. If the fluvial regime were controlled primarily by elevation, and assuming no significant sequestration, lower elevations should have greater overall runoff production due to the accumulation of flow from upslope. The difference between breached and unbreached craters could therefore represent glacial melting occurring within craters (higher elevation) as opposed to significantly upslope of them (lower elevation), which would instead promote runoff and breaching of craters by valley networks.</span></p><p>We previously described a single CSDB crater that showed evidence for cold-based crater wall glaciation, sedimentation and proglacial lake formation, but this new work adds a significant body of evidence that such processes were operating at much greater regional scales. While runoff from rainfall is usually considered the most likely mechanism of fluvial erosion in the Noachian, the possibility remains that fluvial erosion could have occurred via snowmelt in a subfreezing ambient climate. We have provided compelling evidence that fluvial and lacustrine features could have formed in such a climate and that Noachian Mars may have been colder than previously believed.</p>

Discordance Mapping of Argyre Basin: An Insight into the Fluvial and Subglacial Origin of Valley Networks in the Argyre Basin Region

<p><strong>Introduction:</strong>  Martian valley networks are evidence for surface run-off and past water cycles on ancient Mars. Many of the networks resemble terrestrial precipitation-fed systems; however, recent analysis has found that the geometries and morphological characteristics of some valley networks are more comparable to subglacial valley formation. Subglacial valleys have morphological characteristics that make them distinct from fluvial valley systems (i.e., those formed via precipitation or sapping erosion). Unlike fluvial valley networks, which follow the surface slope of the underlying topography, sub-glacial networks are orientated in the direction of the surface slope of the overlying ice-sheet. Therefore, subglacial valleys may have orientations that are discordant with the underlying topography. Discordance analysis, a technique that compares the valley paleoslope direction and topographic slope direction, has been applied to Mars to determine areas that have undergone topographic modification since valley formation. This technique could also be a tool for identify valleys with potential sub-glacial origins.</p><p>In this study, we mapped and applied discordance analysis to valley networks in and around Argyre basin. Detailed analysis was performed on four valley networks on eastern Argyre, to determine whether their characteristics are indicative of a fluvial or sub-glacial origin.</p><p><strong>Results:</strong> 2669 V-Shaped valleys (total length = 36155.5 km) and 45 U-Shaped valleys (total length = 2683.5 km) were identified. Most V-Shaped valleys dissect the eastern and northern rim of Argyre Basin, with fewer in the south and west. The densest northern valley networks have values up to 0.098 km<sup>-1</sup>, compared to the densest in the south with values of only 0.040 km<sup>-1</sup>. U-Shaped valleys are prominent along the south/south-west rim, but are lacking along the northern rim of Argyre.</p><p>Most valleys (47.8 %) are concordant (< 45° discordance) with present slope direction. Two dense groups of discordant valleys are present adjacent to Hale Crater and Nia Vallis. These areas display features associated with the presence of an ice-sheet/glacier – e.g., glacial moraines and eskers. Additionally, the morphology of these valley systems are consistent with a subglacial origin.</p><p>Fento Vallis and the Darwin Crater valley system are concordant with present topographic slope, and are in close proximity to one another; however, their morphologies differ greatly. Fento Vallis consists of 25 valleys (total valley length of ~ 690 km) and drainage density of 0.019 km<sup>-1</sup>. The Darwin Crater valley network consists of 49 valleys (total valley length of ~ 1351 km) and drainage density of 0.048 km<sup>-1</sup>. Fento Vallis displays features (e.g., inner channel eskers) indicative of a subglacial origin. Alternatively, the Darwin Crater System has a planform associated with fluvial activity and originates from cirque like depressions. Although the Darwin Crater system appears to have a fluvial origin, less than 100 km to the east is Pallacopas Vallis, which displays inner eskers indicating that it has a subglacial origin.</p><p>Three of the networks analysed, which are > 1000 km apart from one another, are likely subglacial in origin. Their occurrence indicates that an ice-sheet or multiple ice-sheets were present along the eastern region of Argyre throughout its history.</p>

The global distribution of depositional rivers on early Mars

Sedimentary basins are the archives of ancient environmental conditions on planetary surfaces, and on Mars they may contain the best record of surface water and habitable conditions. While erosional valley networks have been mapped, the global distribution of fluvial sedimentary deposits on Mars has been unknown. Here we generated an eight-trillion-pixel global map of Mars using data from the NASA Context Camera (CTX), aboard the Mars Reconnaissance Orbiter spacecraft, to perform the first systematic global survey of fluvial ridges—exhumed ancient deposits that have the planform shape of river channels or channel belts, but stand in positive relief due to preferential erosion of neighboring terrain. We used large fluvial ridges (>70 m width) as a conservative proxy for the occurrence of depositional rivers or river-influenced depositional areas. Results showed that fluvial ridges are as much as 100 km long, common across the southern highlands, occur primarily in networks within intercrater plains, and are not confined to impact basins. Ridges were dominantly found in Noachian through Late Hesperian units, consistent with cessation of valley network activity, and occurred downstream from valley networks, indicating regional source-to-sink transport systems. These depositional areas mark a globally distributed class of sedimentary deposits that contain a rich archive of Mars history, including fluvial activity on early Mars.

Fluvial incised networks on top of late Ordovician interglacial valley buried hills as the result of post glacial isostatic rebound; 3D seismic input

<p>It is classically assume that prior to deep glacial valleys incision below large scale ice cap, often interpreted as the results of ice flow melting during tidewater period, the initial glacial topography was flat or very low angle and created during a major phase of cold glaciers advance as suggested by quaternary studies. Therefore up to now we have assume that the top of late Ordovician buried hills separating major glacial valleys was the remains of this flat surface truncating the pre-glacial Ordovician Hawaz series, later on flooded by the Lower Silurian. Surprisingly by reinterpreting 3D seismic cubes using spectral decomposition technics on the Murzuk basin in SE Libya, it appears that the top of buried hills are not at all characterized by a flat erosional surface, but it is strongly irregular and shows the development of narrow valley networks displaying the classical dendritic erosional pattern diagnostic of fluvial erosion. These small valleys are organized into a tributary network and don’t flow toward the ice margin, i.e. toward the N-NW but most of the time flow at right angle toward the adjacent main glacial valleys which are pointing toward the NW. These narrow valley networks in this context could be either glacial tunnel valleys located at the periphery of the ice cap in close relationships with glacial fronts (their common settings) or could correspond to fluvial valleys developed later on, in a subaerial setting at some distance from glacial fronts; we retain this second interpretation because in addition to the geomorphic features: (1) they flow parallel to the fronts that we have already recognized, Moreau et al. (2005), Rubino et al.  2007 and (2) they are suspended in the sense that these lateral networks do not reach the bottom of the main glacial valley but, they appear to be connected within the upper part of the glacial infill, immediately below the early Silurian post glacial flooding characterized by the well-known Rhuddanian hot shales. As a result, the incision of the valley network appears quite late in the ice cap melting history. It is why we tend to interpret these valleys erosion as the result of post glacial melting during ice retreat at some distance from the ice front and strongly enhanced by isostatic rebound. Some possible modern analogs of such valley fringing highs may exist in Artic Canadian islands.</p>