Reconstruction of Northwestern Terra Cimmeria Watersheds
Authors: Cuřín Vojtěch , Markonis Yannis 
Published: September 2022

&lt;p&gt;Abstract&lt;/p&gt;
&lt;p&gt;Northwestern part of Terra Cimmeria displays a wide range of fluvial, lacustrine and glaciofluvial geomorphological features, indicative of presence of liquid water in this area early in the Martian history. These features were previously mapped as part of global studies, but not in relation to the area itself. Here we present our reconstruction of hydrologically correct model of northwestern Terra Cimmeria based on algorithm assisted mapping exercise of unprecedented precision. Based on our findings we are able to contextualize the geomorphological specifics of individual subbasins within the framework of Late Noachian Icy Highlands model and subsequent climatic transition towards the dry and cold state of the Amazonian period.&lt;/p&gt;
&lt;p&gt;Physiographic Characteristic&lt;/p&gt;
&lt;p&gt;Terra Cimmeria is an extensive region of the Martian southern highlands. Its northwestern portion (Northwestern Terra Cimmeria, NWTC) lies in the equatorial area of the planet and likely did so even before the Tharsis-induced true polar wander event (Bouley et al., 2016). It is nested between the volcanic province of Hesperia Planum to the southwest and the Utopia highland-lowland boundary to the north (Skinner and Tanaka, 2007). In the setting of the disputed Arabia Level ocean shoreline (Sholes et. al, 2021 and references therein) NWTC would stand out as the longest peninsula on Mars. The surface of NWTC is dominated by the Late Noachian highland unit with &amp;#8222;undifferentiated impact, volcanic, fluvial and basin material&amp;#8220; (Tanaka et al., 2014). There are several open-basin lakes as mapped by Fassett and Head (2008), craters in different stages of degradation, and numerous valley networks which dissect the terrain (Carr, 1995; Hynek et al., 2010; Alemanno et al., 2018) and few on which terminate as deltaic deposits previously mapped by Achille and Hynek (2010). The variety and density of geomorphological features whose formation is tied to the presence of volatiles suggests a rich history of fluvial, lacustrine, and glaciofluvial activity and importantly fluvially dominated erosion and deposition. We incorporated available imagery and previously derived datasets in our algorithm assisted mapping exercise in order to contextualize the putative sources of the valley carving runoff within the local climatic background.&lt;/p&gt;
&lt;p&gt;Methodology&lt;/p&gt;
&lt;p&gt;NWTC valley networks were mapped several times in different level of detail starting with Carr (1995) who based his mapping on Viking imagery. This initial campaign was followed by Hynek et al. (2010) who utilized THEMIS daytime IR imagery and MOLA DEM and later by Alemanno et al. (2018) who in addition to THEMIS daytime IR and MOLA DEM used the ConTeXt (CTX) camera imagery to improve their recognition capability where the forementioned datasets lacked sufficient resolution.&lt;/p&gt;
&lt;p&gt;Our mapping is based on the high resolution global CTX image mosaic rendered at 5 m/pixel (Dickson et al., 2018), THEMIS nighttime IR dataset, and MOLA DEM with the vectorized valley network dataset of Alemanno et al. (2018) serving as a baseline. We used Whitebox GAT surface flow accumulation model with hybrid breaching-filling sink removal capability (Lindsay, 2015) to digitalize the thalwegs as well as subbasins based on MOLA DEM. The algorithm-derived thalwegs and previously mapped valley networks were used to guide and double check the manual mapping which was based strictly on the CTX and THEMIS nighttime IR mosaics. Subsequently, digitalized subbasin borders were checked against the CTX mosaic and corrected based on the underlaying terrain. Notable geomorphological features were identified and marked as point features and putative headwater areas we delineated based on the previously logged data.&lt;/p&gt;
&lt;p&gt;Results&lt;/p&gt;
&lt;p&gt;We mapped an area spanning more than 8&amp;#10005;10&lt;sup&gt;5&lt;/sup&gt; km&lt;sup&gt;2&lt;/sup&gt; and reconstructed 7 main valley networks. The valley networks were divided into over 80 subbasins based on manual correction of flow accumulation model. We managed to identify and connect seemingly isolated stretches of valleys and incorporate them into their respective networks thus creating a hydrologically correct reconstruction of the area. We identified several headwater-specific geomorphic features, pingos and paleolakes.&lt;/p&gt;
&lt;p&gt;Discussion&lt;/p&gt;
&lt;p&gt;In Noachian NWTC was situated between the equilibrium and terminus lines of a Late Noachian Icy Highlands (LNIH) ice sheet (Fastook and Head, 2015) and as such it would favor the formation of subglacial channels fed by meltwater (Galofre et al., 2020) and accumulation of ice (Wordsworth et al., 2013; Fastook and Head, 2015). The presence of developed dentritic networks which could have been carved by glavial meltwater is proven by our mapping exercise. Head et al. (2022) proposed that the climate of Mars underwent a transitional period during which a decrease in the atmospheric pressure induced a shift from altitude dependent temperature regime typical for the Noachian period (Wordsworth et al., 2013) towards latitude dependent temperature regime of the Amazonian period. This transition would start with ablation and melting of the lower altitude icy deposits and end with desiccation of equatorial ice reservoirs &amp;#8211; both of which are in broader sense applicable to NWTC. In the beginning of this transitional period, meltwater released during the phases of peak temperatures would return to the highland cold traps in the time between these episodes. It is therefore plausible that given the specific combination of altitude, latitude, and location of NWTC, this area could sustain active surface or near-subsurface hydrology for an extended period of time up to 10&lt;sup&gt;6&lt;/sup&gt; -10&lt;sup&gt;8&lt;/sup&gt; years. This is supported by the variety of geomorphic features present in NWTC, but remains to be further tested with buffered crater counting and development of conceptual and hydrological models based on the newly created datasets.&lt;/p&gt;
&lt;p&gt;Acknowledgements&lt;/p&gt;
&lt;p&gt;VC &amp; YM were supported by Czech Science Foundation (#20-27624Y).&lt;/p&gt;
&lt;p&gt;References&lt;/p&gt;
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