Geologic map of the Terra Cimmeria-Nepenthes Mensae transitional zone, Mars – 1:1.45Million

ABSTRACT A 1:1.45Million geologic map of NW Terra Cimmeria and SE Nepenthes Mensae (-5°31’–5°38’ N, 119°20’–129°55’ E) is presented here, displaying one of the highland-lowland transitional zones of Mars with greatest contrast and diversity. The Terra Cimmeria-Nepenthes Mensae Transitional Zone comprises two complex and poorly studied geologic domains bounded by the dichotomy escarpment. The map produced in this work displays nineteen geologic units and numerous geomorphic features. Detailed mapping, morphologic and morphometric analyses and Poisson model-derived ages have permitted to constrain the stratigraphy of this transitional zone and reconstruct more accurately its geological history from the Early Noachian to recent times, suggesting a significant period of fluvial activity within the Early Amazonian. The map provides insight into the processes involved in the origin and development of this transitional zone and offers a reference geologic framework for future studies in the region.


Introduction
Studies carried out in the highland-lowland transitional zone of Mars permit us to shed light into the geologic processes involved in the origin and evolution of the dichotomy boundary and its nearby areas, as well as to improve our understanding of the early history of Mars (e.g.Levy et al., 2007;McGill & Dimitriou, 1990;Watters, 2003aWatters, , 2003b;;Watters & McGovern, 2006).This work focuses on one of the most contrasting highland-lowland transitional zones: the ancient and densely-cratered highland plateaus of the northwestern part of Terra Cimmeria, south of the dichotomy boundary, and the relatively young and poorly-cratered lowland plains of the southeastern area of Nepenthes Mensae, north of Terra Cimmeria, mapped as Middle Noachian highland unit (mNh) and Hesperian and Noachian transition unit (HNt), respectively (Tanaka et al., 2014) (Figure 1).These geologic domains in the equatorial region of Mars are bounded by the dichotomy escarpment with a local relief of ∼2 km.The Terra Cimmeria-Nepenthes Mensae Transitional Zone (CNTZ), which remains as a complex and poorly studied area (e.g.Skinner & Tanaka, 2018), is characterized by: (1) tectonically-contracted areas as inferred by the occurrence of lobate scarps, ridge crests and wrinkle ridges in the Terra Cimmeria (e.g.Watters, 2003b;Watters & Robinson, 1999) and Nepenthes Mensae regions; (2) fracture-controlled linear troughs in the vicinity of the dichotomy escarpment, probably generated by extensional tectonic deformation and/or lateral spreading along the escarpment (e.g.Irwin III et al., 2004); (3) interconnected NW-SE-trending closed depressions at the foot of the dichotomy, probably related to extensional tectonics (Watters, 2003a;Watters & McGovern, 2006); and (4) pervasive residual reliefs probably related to mass-wasting processes and 'basal sapping of volatiles' in Nepenthes Mensae (Tanaka et al., 2005).Fluvio-lacustrine activity seems to have played a fundamental role in the configuration of the CNTZ, as indicated by the presence of ancient V-shaped fluvial valleys in the Cimmeria region (e.g.García-Arnay et al., 2018b;Goudge & Fassett, 2018;Irwin & Howard, 2002), as well as moderately preserved Gilbert-type deltas and alluvial fans at their mouths (e.g. de Pablo & Pacifici, 2008;García-Arnay et al., 2018a, 2018b;García-Arnay & Gutiérrez, 2020, 2023;Irwin et al., 2005;Rivera-Hernández & Palucis, 2019).Furthermore, the occurrence of putative deltas and paleoshore platforms spatially associated with closed depressions in Nepenthes Mensae suggest the presence of paleolakes (García-Arnay & Gutiérrez, 2020).The study area has been included over time in multiple geologic maps produced by the United States Geological Survey CONTACT Ángel García-Arnay arnay@unizar.esGrupo Procesos Geoambientales y Cambio Global, IUCA, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain This article has been corrected with minor changes.These changes do not impact the academic content of the article.
Supplemental data for this article can be accessed here https://doi.org/10.(USGS) (e.g.Greeley & Guest, 1987;Hiller, 1979;King, 1978;Scott & Carr, 1978;Tanaka et al., 1992;Tanaka et al., 2005;Tanaka et al., 2014).However, the scale of these maps precludes the representation of important features.Recently, several regional-scale geologic maps have been produced surrounding the CNTZ: the transitional zone between Terra Cimmeria and Utopia Planitia by Skinner and Tanaka (2018), northwest of the study area, providing a reference framework to compare with the CNTZ, and Aeolis Dorsa by Burr et al. (2021), southeast of the mapped area in this work.Furthermore, García-Arnay and Gutiérrez (2023) carried out a local-and regional-scale geological study in the central sector of the CNTZ, representing about 35% of the area mapped in this work.This study provided insight into the endogenic and exogenic processes involved in the configuration of this part of the CNTZ, including a geological-geomorphological map that comprises 18 geologic units.This work presents a detailed regional-scale geological map of NW Terra Cimmeria and SE Nepenthes Mensae providing insight into the processes involved in the configuration of this transitional zone, focusing on (1) the identification, description and interpretation of the different geologic units and geomorphic features; (2) the estimation of the chronology of the main surface units; and (3) the reconstruction of the protracted geological-geomorphological history.

Imagery and topographic data
The utilized visible imagery comprised the global CTX image mosaic acquired by the Context Camera (CTX, 5-6 m/pixel) (Dickson et al., 2018;Malin et al., 2007), and additional images from the High Resolution Imaging Science Experiment (HiRISE, ∼25-50 cm/pixel) (McEwen et al., 2007), both instruments on board NASA's Mars Reconnaissance Orbiter.Infrared imagery included the daytime infrared image mosaic obtained by the Thermal Emission Imaging System (THEMIS, 100 m/pixel) (Christensen et al., 2004(Christensen et al., , 2013)), on board NASA's Mars Odyssey.The qualitative mosaic of the THEMIS-based thermal inertia (TI) (Fergason et al., 2006), which is derived from THEMIS nighttime infrared images, was used to differentiate surface materials (Figure 1(c)).
Topographic data were extracted from Digital Elevation Models (DEMs) derived from the Mars Orbiter Laser Altimeter (MOLA, 463 m/pixel) (Zuber et al., 1992), on board NASA's Mars Global Surveyor, as well as from the High Resolution Stereo Camera (HRSC, 50-75 m/pixel), on board ESA's Mars Express.A HRSC and MOLA blended DEM (Fergason et al., 2018, ∼200 m/pixel) was used to cover areas where HRSC data are not available.In order to map the geologic units and landforms, establish their geometrical relationships, and carry out morphological and morphometric analyses, data were integrated into a Geographic Information System (Esri's ArcGIS 10.5.1) and projected into the geographic coordinate system 'GCS_Mars_2000_Sphere', with an equidistant cylindrical projection and a central meridian of 125°E.

Mapping methods
The geologic map was produced applying methodologies and techniques widely used in planetary geological mapping (e.g.Greeley & Batson, 1990;Wilhelms, 1990), and in geological mapping of Mars (e.g.Skinner & Tanaka, 2003;Skinner & Tanaka, 2018;Tanaka et al., 2014).Visible and infrared imagery together with topographic data were used to identify, interpret and correlate the surface units, largely on the basis of their primary surface features (Skinner & Tanaka, 2003).The THEMIS daytime infrared images were used as a primary base map, whereas CTX and HiRISE images, as well as the TI mosaic, were used as supplementary datasets.The name of the mapped units was based on their geographic location, where applicable, prevalent features and/or origin, as well as stratigraphic relationships (Hansen, 2000;Skinner & Tanaka, 2018;Tanaka et al., 2005).The drainage network was drawn automatically applying the 'Hydrology' toolset in ArcGIS, and later improved by removing manually artifacts using visible imagery and TI data.The proximal edges of fan-shaped features were delineated where the paleoflows debouching from the valleys used to become unconfined (García-Arnay & Gutiérrez, 2020).All crater rims >5 km in diameter have been mapped.The different preserved components of craters ≥13 km in rim diameter were depicted in the map.However, the 'Crater unitundivided', which comprises well-preserved crater materials with rim diameters between 5 and 13 km, does not distinguish among crater-related components due to their relatively small size compared to the map scale.Azimuth data from selected mapped landforms were plotted on rose diagrams with the GeoRose 0.5.1 software (Yong Technology Inc.) (Figure 3).

Chronology of surface units
The chronological ascription of map units was addressed from the formation age estimates derived from crater size-frequency distributions and their geometrical relationships (see Figure 4).Crater populations for each unit of interest were mapped and computed using the 'CraterTools' toolset for Esri's ArcGIS (Kneissl et al., 2011).All primary craters larger than 50 or 100 m in rim diameter with centroids within the count area were mapped.Crater-counting areas larger than 1000 km 2 were selected, where possible, to minimize the potential bias related to the variable cratering pattern (Warner et al., 2015).Surfaces occupied by well-preserved ejecta blankets were excluded from the count areas, except when it was necessary to estimate the formation age of the associated impact event.Cumulative crater size-frequency diagrams for each sampling area were generated using the CraterStats2 software (Michael & Neukum, 2010), and the absolute model ages were derived from chronology and crater production functions defined by Hartmann (2005).Age estimates were determined using a different method from the one applied in García-Arnay and Gutiérrez ( 2023) to obtain more confident results, mostly with model ages derived from smaller counting areas.This approach uses the Poisson timing analysis technique, which expresses the result as a probability function that incorporates inherent uncertainty, as well as the μ function (Michael et al., 2016), instead of the binning/best-fit approaches used by García-Arnay and Gutiérrez (2023).

Geologic units of the CNTZ
The map differentiates 19 units (18 out of them previously described by García-Arnay & Gutiérrez, 2023) that have been grouped according to their geographic distribution (see the geological map in 'Supplementary material').Three units have been identified in the Cimmeria region of the highland province: The Cimmeria dissected units include two welldifferentiated members with rugged and heavily cratered surfaces dissected by V-shaped valleys (e.g.Skinner & Tanaka, 2018;Tanaka et al., 2005Tanaka et al., , 2014)).Member a (Nhcd a ) occurs in the topographically higher sector, whereas member b (Nhcd b ) crops out in the plateau situated south of the dichotomy, at lower elevation than member a, forming residual reliefs (knobs and mesas) in the transitional province (Figure 2(a)).Member a (Nhcd a ) shows a higher crater density than member b, NW-SE-striking lobate scarps, and less commonly ridge crests (Figure 2 Three units have been recognized in the Nepenthes Mensae region of the transitional province: The Nepenthes knobby plateau unit (Ntn kp ) is a moderately cratered unit that occurs in the inter-crater plateaus of Nepenthes Mensae, characterized by knobby terrains with residual hills made up of materials of the unit Nhcd b and mass-wasted materials (e.g.Tanaka et al., 2005) (Figure 2(c)).This unit, with a gradational boundary with the older unit Nhcd b and the younger unit HNtn b , shows NW-SE-trending lobate scarps and yardangs with pervasive NW-SE orientation.The Nepenthes basin unit (HNtn b ) crops out in the NW-SE-trending closed depressions at the foot of the dichotomy escarpment, which used to host paleolakes (García-Arnay & Gutiérrez, 2020; Rivera-Hernández & Palucis, 2019), as well as on floors of poorly-preserved impact basins.The Nepenthes basin unit, which overlies unit Nhcd b , is characterized by a lower crater density than unit Ntn kp , and relatively smooth terrains locally interrupted by residual reliefs, wrinkle ridges, pitted cones and small tholi.The Nepenthes ridged plain unit (AHtn rp ) that occurs in the northeast sector of the map exhibits undulating, low-lying plains with pervasive NW-SE-oriented wrinkle ridges and scattered knobs of unit Nhcd b (Figure 2(d)).This unit, which is less-cratered than units Ntn kp and HNtn b , overlies unit Nhcd b and grades into the older unit Ntn kp .
Seven impact crater units have been distinguished.Well-preserved craters with rim diameter between 5 and 13 km were mapped as the crater unit-undivided (AHc u ).This unit is frequently characterized by hummocky crater floors with rare occurrence of central peak or pit, and lobate ejecta deposits.The preserved morpho-structural components of moderately to well-preserved impact craters with rim diameter ≥13 km were mapped: The crater floor unit (ANc f ) is characterized by smooth, near-planar surfaces, frequently displaying a central peak and/or pit in the center of the crater (Figure 2(b)).The crater peak unit (ANc p ) shows hills with irregular and grooved surfaces, and frequent occurrence of central pits.The crater wall unit (ANc w ) comprises scarps, discontinuous terraces, blocks, and rockfalls with locally rugged surfaces.The rim crater unit (ANc r ) is formed by inwardfacing scarps frequently dissected by gullies.The crater ejecta units include two morpho-facies: (1) the crater ejecta unit-facies a (ANce a ), which represents the inner unit characterized by rugged lobes with flowbands, and (2) the crater ejecta unit-facies b (ANce b ) corresponds to the distal deposits that are formed by smooth flow-oriented lobes (Figure 2(e)).
Six spatially-dispersed units have been mapped: The volcanic flow unit (ANv f ), which crops out in the deeper areas of the depressions of Nepenthes Mensae, and locally in the highlands near the dichotomy.It exhibits smooth to rugged, poorly-cratered surfaces, often with channels, overlapping lobes, and NE-SWstriking wrinkle ridges (Figure 2(f-i)).This unit locally grades into the coeval unit ANv e , locally overlies units HNtn b and Nhcd b , and underlies unit ANf.The volcanic edifice unit (ANv e ), which is laterally associated with unit ANv f , is characterized by isolated and coalesced raised fissures with sloping, and rugged to smooth surfaces, as well as small cone-and moundshaped features (Figure 2(i-k)).The valley unit (ANv) that is carved in units Nhcd a and Nhcd b , and rarely in unit Ntn kp displays smooth deposits underlying the low-TI valley floors (Figure 2(k, l)).The fan unit (ANf), which is laterally associated with unit ANv, is related to fan-shaped deposits with smooth to corrugated surfaces due to differential erosion (Figure 2

Geomorphic features
The main landforms that occur within the geological units have also been mapped.Two types of scarps were differentiated: (1) Lobate scarps are linear to sinuous, NW-SE-oriented ridge-like landforms (Figure 3  (2) Ridge crests are ridges that display a near-symmetric transverse profile (e.g.Watters et al., 2009).They frequently occur in units Nhcd a and Nhcd b with a dominant NE-SW orientation, and a secondary NW-SE trend (Figure 3(c)).( 3) Volcanic ridges are linear to curvilinear ridges related to fissure vents in unit ANv e that display smooth to rugged slopes, and weak NE-SW and NW-SE prevalent orientations.(4) Channel ridges, often known as 'inverted channels', related to relief inversion by differential erosion are characterized by a sinuous pattern and scarcely occur in valley floors and fans (e.g.Burr et al., 2010).
Four types of negative relief morphologies were distinguished: (1) Troughs are linear to curvilinear steepwalled depressions (Figure 2(a)).These landforms, which form a distinctive polygonal pattern with a dominant NW-SE orientation and a secondary NE-SW trend (Figure 3(d)), occur in the vicinity of the dichotomy cutting into unit Nhcd b .(2) Valleys are networks of V-shaped, steep-walled depressions with linear to sinuous trace and dendritic to trellis pattern (Figure 2(k, l)).Their path seems to be locally controlled by lobate scarps, ridge crests and troughs, with evidence of deflections.(3) Channels are linear to sinuous, shallow and narrow depressions occurring in the valley floors, locally with positive relief sections.The channel networks mostly occur in units Nhcd a and Nhcd b and scarcely in unit Ntn kp .They exhibit an orthogonal pattern with a dominant NE-SW orientation, and a secondary NW-SE trend, probably controlled by fractures.It is common the occurrence of knickpoints, as well as defeated and beheaded channels.(4) Pit craters are elongated, closed depressions with scarped boundaries (e.g.Parenti et al., 2020).The major axis of these features that locally occur in unit ANv f display a predominant NW-SE orientation.
Two types of mound-and cone-shaped landforms associated with unit ANv e were mapped: (1) Pitted cones are conical hills with smooth slopes and central pits (e.g.Skinner & Tanaka, 2018) (Figure 2(i, j)).These landforms occur in unit ANv f , and less frequently in units Ntn kp and HNtn b .(2) Small tholi, which generally occur in unit ANv f and rarely in unit HNtn b , are mounds often exhibiting central peaks and subtle outward-facing slopes bounded by marginal scarps (e.g.Skinner & Tanaka, 2018).
The obtained age estimates using the Poisson timing analysis method are generally younger and have larger error ranges compared to those estimated in García-Arnay and Gutiérrez (2023) for smaller counting areas (e.g. the fan unit).In contrast, age estimates obtained for larger counting areas generally show consistency with both approaches.

Interpretation and correlation of map units
The interpretation of the geologic units and landforms and their chronological ascription, based on both geometrical relationships and crater counts, is summarized here (see Figures 4 and 5).

Early to Middle Noachian epochs
The documented stratigraphic record of the CNTZ began in the Early to Middle Noachian, with the emplacement of units Nhcd a and Nhcd b in the Cimmeria region, interpreted as moderately to heavily degraded undifferentiated highland materials related to impact, volcanic, basin-fill, and fluvial processes.Both units form part of the unit mNh (Middle Noachian) defined by Tanaka et al. (2014).The unit Nhcd b possibly also correlates with unit Nhc 1 (Early to Middle Noachian) mapped by Skinner and Tanaka (2018).The widespread occurrence of lobate scarps related to thrust faults (e.g.Watters & Robinson, 1999) suggests that these units were affected by NE-SW-oriented tectonic shortening (García-Arnay & Gutiérrez, 2023).

Late Noachian epoch
In the Late Noachian, uncertain-origin depressions inset into unit Nhcd a were filled by sediments to form unit Nhc b , consisting of slightly to moderately degraded undifferentiated deposits probably related to fluvial, basin-fill and impact processes.This tectonically contracted unit, as inferred by wrinkle ridges attributed to thrust faults (e.g.Andrews-Hanna, 2020), likely correlates with unit lNh (Late Noachian)  defined by Tanaka et al. (2014).The Nepenthes Mensae region is characterized by knobby terrains, probably generated by basal sapping and mass-wasting processes (Tanaka et al., 2005), as well as a belt of large extensional depressions and troughs (e.g.Watters, 2003a).The unit Ntn kp is probably formed by undifferentiated materials attributed to volcanic and impact products, and mass-wasted deposits forming aprons around knobs and mesas of the unit Nhcd b .This tectonically contracted unit, with morphotectonic features indicating a NE-SW shortening trend, was formed during the Late Noachian.According to García-Arnay and Gutiérrez (2023), the extensional tectonics, which seems to begin during the Late Noachian, probably led to the development of: (1) the 2km-high dichotomy boundary interpreted as a fault scarp related to a master normal fault.(2) The system of interconnected NW-SE-trending closed depressions in Nepenthes Mensae.These basins appear to correspond to keystone grabens associated with the master fault of a larger half-graben morpho-structure featuring a rollover anticline.(3) The plateau located to the south of the dichotomy boundary in Terra Cimmeria with down-to-the-north topographic drops associated with secondary normal faults.(4) The fissure-type volcanism in the deepest areas of the depressions in Nepenthes Mensae.(5) The mega landslides derived from the dichotomy escarpment.

Hesperian period
The locally contracted unit HNtn b , that is probably underlain by lacustrine, fluvial, and mass-wasted materials ascribed to the Late Noachian and Early Hesperian, is related to the paleolake basins (e.g.García-Arnay & Gutiérrez, 2020).The units Ntn kp and HNtn b are integrated into unit HNt (Noachian and Hesperian periods) by Tanaka et al. (2014).The units Nhc 2 (Middle to Late Noachian) and HNhc 3 (Late Noachian to Early Hesperian) defined by Skinner and Tanaka (2018) may correlate with the mapped units Ntn kp and HNtn b , respectively.

Early Amazonian epoch
From the Late Noachian, fluvial activity started to carve units Nhcd a and Nhcd b to form the valley networks and associated putative deltas and alluvial fans corresponding to units ANv and ANf, respectively, most probably lasting up to Early Amazonian times, as suggested by the formation ages obtained for the most of the analyzed fans/deltas.These age estimates are younger in comparison with those published by García-Arnay and Gutiérrez (2023).Fluvial valleys are locally disrupted by thrust faults and transformed into beheaded drainages.The unit AHtn rp , formed during Late Hesperian to Early Amazonian times, consists of tectonically contracted materials related to impact, mass-wasting, fluvio-lacustrine and volcanic processes.It likely correlates with the unit eHt (Early Hesperian) defined by Tanaka et al. (2014).The units ANv e and ANv f are ascribable to different types of volcanic edifices and high-TI lava fields, respectively.Pitted cones exhibit a geometric shape similar to mud volcanoes reported in the northern plains.However, their spatial association with the volcanic flow unit (ANv f ) and fissure vents suggests a hydrovolcanic origin (e.g.tuff cones), as also indicated by Brož and Hauber (2013) in and around Nepenthes Planum region.These genetically-linked units, which are integrated into unit HNt of Tanaka et al. (2014), were coevally emplaced from Late Noachian to Early Amazonian times, suggesting that the extensional phase may have even been active until Early Amazonian times.

Middle to Late Amazonian epochs
The unit ANl consists of deposits related to large landslides (e.g.rock spreads, slumps and falls) that were probably accumulated from the Late Noachian to the Middle Amazonian.Through the Amazonian period, eolian activity formed the dune fields of unit Ae, as well as erosional landforms like yardangs and wind streaks, indicating a persistent SE-directed wind.

Conclusions
The production of the 1:1.45M geologic map of the NW Terra Cimmeria and SE Nepenthes Mensae has permitted to (1) constrain the stratigraphy of this poorly explored highland-lowland transitional zone of Mars, differentiating nineteen geologic units that include a wide variety of geomorphic features; and (2) reconstruct its long-term geological history that ranges from the Early Noachian to recent times.The Poisson model-derived ages generally show consistency with those estimated by binning/best-fit approaches for larger counting areas.In contrast, significant younger age estimates were obtained for smaller counting areas.The mapping has also shed light on the role played by the inferred compressional and extensional tectonics, as well as the fluvio-lacustrine activity on the configuration of the landscape in the CNTZ from Late Noachian to Early Amazonian.This work provides a detailed geologic framework for future studies within this transitional zone, of special interest from the paleohydrological perspective and for understanding the evolution of early Mars.

Software
Esri's ArcGIS 10.5.1 was used for mapping, performing multiple analyses and generate the layout of the map.The final editing of the map was carried out using Adobe Illustrator CS6 and Adobe Photoshop CS4.Azimuth data were plotted with the GeoRose 0.5.1 software (Yong Technology Inc.).'CraterTools' toolset for Esri's ArcGIS (Kneissl et al., 2011) and 'CraterStats2' software (Michael & Neukum, 2010) were used to map and compute the crater populations, and generate the crater size-frequency diagrams, respectively.

Figure 1 .
Figure 1.(a) Colorized elevation model (km above Martian datum, a.m.d.) derived from HRSC-MOLA blended data over a mosaic of THEMIS-IR day images, with the study area framed by a red rectangle.White polygons and squares indicate the location of the images of Figure 2. (b) Study area with black polygons indicating the crater-counting areas selected for dating the main surface units (Figure 4(a)).The white line indicates the trace of the geological cross-section (A-A') (Figure 5).(c) Qualitative THEMIS-derived TI mosaic of the study area over THEMIS-IR day images.
(b)).Member b (Nhcd b ) with a gradational boundary with the older member Nhcd a is characterized by localized NE-SWoriented ridge crests, and scarce occurrence of lobate scarps with NW-SE orientation.It shows deeper valleys with a dominant NE-SW orientation, and a secondary NW-SE trend near the dichotomy boundary.The Cimmeria basin unit (Nhc b ) is a moderately cratered unit that occurs in depressions inset into member Nhcd a , exhibiting smooth surfaces, wrinkle ridges, and absence of channels (Figure 2(b)).

Figure 2 .
Figure 2. CTX images showing remarkable landforms in the CNTZ (locations indicated in Figure 1(a)).(a) Mesa-like landform in a megalandslide dissected by troughs related to fracture-controlled gravitational extension.(b) SW-facing lobate scarp attributable to a surface-rupturing thrust fault occurring in unit Nhcd a .(c) Knobby terrain of unit Ntn kp displaying wind streaks.(d) Tectonicallycontracted plains of unit AHtn rp exhibiting wrinkle ridges and knobs.(e) Morpho-facies ANce a and ANce b related to the crater located at 129°E, 1°N.(f-h) Volcanic plains of unit ANv f exhibiting probable collapse lava tubes.(i) Volcano-like pitted cones of unit ANv e and probable collapse lava tubes of unit ANv f .(j) Volcano-like pitted cone of unit ANv e and dark-tone barchan dune fields of unit Ae. (k) Putative Gilbert-type delta and volcanic features such as fissure vents and lava fields.(l) Paired terraces in Licus Vallis.North is up in all images.
(k)).The landslide unit (ANl) mostly occurs associated with the dichotomy escarpment locally overlying units Nhcd b and HNtn b .It is characterized by rugged, rolling, and hummocky terrains.The eolian unit (Ae) consists of dark-tone, barchan and longitudinal dune fields occurring near the foot of the dichotomy, and locally overlying units ANv f , ANc f , ANv, HNtn b and Nhcd b (Figure 2(j)).

Figure 3 .
Figure 3. Rose diagrams displaying the distribution of the orientation of lobate scarps (a), wrinkle ridges (b), ridge crests (c), and troughs (d).n: number of features.

Figure 4 .
Figure 4. (a) Diagram showing age estimates (red and blue boxes for formation and resurfacing ages, respectively), and their error bars (vertical black lines) from the crater size-frequency diagrams for the main mapped units (see Figure A1).(b) Correlation of map units based on ages estimated by crater counting and geometrical relationships between units.Hachured polygon borders indicate possible, extended durations.Horizontal continuous and dashed lines indicate the boundaries between the Martian geological periods and epochs, respectively(Michael, 2013).

Figure 5 .
Figure 5. Geological cross-section A-A' (see location in Figure 1(b)) constructed on the basis of cartographic relationships and crater-counting-based ages (Figure 4).