Icarus 245 (2015) 122144Contents lists available at ScienceDirect

Icarus

journal homepage: www.elsevier .com/ locate/ icarusAmazonian modification of Moreux crater: Record of recent and episodicglaciation in the Protonilus Mensae region of Marshttp://dx.doi.org/10.1016/j.icarus.2014.09.0280019-1035/ 2014 Elsevier Inc. All rights reserved.

Corresponding author at: PLANEX, Physical Research Laboratory, Navrangpura,Ahmedabad 380 009, India. Fax: +91 79 2631 4407.

E-mail address: murty@prl.res.in (S.V.S. Murty).Rishitosh K. Sinha, S.V.S. Murty PLANEX, Physical Research Laboratory, Ahmedabad 380 009, India

a r t i c l e i n f oArticle history:Received 19 December 2013Revised 12 September 2014Accepted 15 September 2014Available online 22 September 2014

Keywords:MarsIcesMars, climateMars, atmosphereMars, surfacea b s t r a c t

Morphologic characteristics of ice-rich landforms in the martian mid-latitudes record evidence for signif-icant modification of the landscape in response to spinaxis/orbital parameter-driven shifts in the LateAmazonian climate. These landforms are spatially distributed across the mid-latitudes and their co-exist-ing presence has so far not been observed from a single crater to infer how exactly a terrain has beenmodified while Mars was undergoing majormoderateminor shifts in its Late Amazonian climate. Wehave therefore carried out an in-depth investigation of Moreux crater (135 km, centered at 41.66N,44.44E in the Protonilus Mensae region) for identification of features associated with recent and episodicglacial events and for emphasizing the role played by these glacial events in the modification of the cra-ter. Evidence for extensive modification of the surfaces over crater rim/wall and around central peak byemplacement of multiple scales of ice-rich landforms that represents large history of glacial activities wasfound. From our results we document phases of majormoderateminor glacial activities within the cra-ter as: (1) piedmont lobes/lobate debris aprons/linear valley fills (1 Ga100 Ma), (2) viscous flow fea-tures (300.1 Ma) and (3) gullies/thermal contraction crack polygons (2.10.4 Ma). The form anddistribution of the random valleys observed within Moreux suggests their formation by pressure-inducedmelting and flow occurring beneath an extensive layer of ice. We also suggest that central peak of Moreuxprobably acted as the locus for accumulation of ice/snow and the diversity of glacial/periglacial featureswithin the crater was possibly controlled by differences in the amount of accumulated ice/snow and therate at which the terrain responded to the shifts in climate during subsequent periods of obliquitychanges. Taken together, these ice-rich deposits within Moreux suggest that sequential modification ofthe crater surfaces over the rim/wall and around central peak has occurred over the last tens of millionsof years of martian history. This new evidence thus adds another well-documented case to rapidly accu-mulating evidences for widespread glacial activity in the middle latitudes of Mars in recent martianhistory.

2014 Elsevier Inc. All rights reserved.1. Introduction

There exist definite geomorphic evidences in the mid-latitudesof Mars that substantiate onset-and-completion of multiple epi-sodes of ice-rich processes during the Late Amazonian geologicalhistory (Carr and Schaber, 1977; Squyres, 1979; Lucchitta, 1981;Squyres and Carr, 1986; Kargel and Strom, 1992; Kargel et al.,1995; Carr, 1996; Baker, 2001; Kargel, 2004; Dickson et al., 2008;Baker et al., 2010; Head et al., 2006, 2010; Hubbard et al., 2011;Sounness and Hubbard, 2012; Sinha and Murty, 2013a, 2013b;Fastook and Head, 2014). These glacial activities have likelyresulted from the accumulation and compaction of snow and iceon plateaus as well as in alcoves within the plateau walls and cra-ter slopes during periods of higher obliquity excursions (Laskaret al., 2004; Head et al., 2003; Forget et al., 2006; Milkovichet al., 2006; Fastook et al., 2011; Dickson and Head, 2009). A vari-ety of glacial/periglacial landforms have been observed between30 and 50 latitude of both the hemispheres, as an outcome ofpertinent glacial processes during the past 1.0 Ga0.4 Ma(Milliken et al., 2003; Neukum et al., 2004; Arfstrom andHartmann, 2005; Milkovich et al., 2006; Dickson and Head, 2009;Baker et al., 2010; Levy et al., 2007, 2009; Morgan et al., 2009,2010, 2011). More than a decade of analyses of these landformsusing multi-resolution images from post-Viking missions hashelped to characterize the extent of glacial processes and theirorigin. Together, these observations have suggested thick deposits

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R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 123of non-polar ice impounded below a surface wrap in these regionsfrom the past hundreds of millions of years, and preserved to date(Holt et al., 2008; Plaut et al., 2009). Therefore, the studies of inter-relationships between these small-large scale glacial/periglaciallandforms, amount of ice/snow involved for their formation, andthe extent of modification they caused have always been givenpreference for understanding the role they played in modifyingthe regional mid-latitude terrain.

Global maps of these glacial/periglacial features from the mid-latitude terrain integrated with the modeling-based predictionsof possible scenario for past deposition of ice/snow have impli-cated the following sources for ice/snow: (1) direct condensationand compaction of seasonally deposited ice/snow (Squyres,1978), (2) remnants from the pre-existing aquifers (Lucchitta,1984; Carr, 2001), and (3) obliquity driven precipitation of snowfrom the atmosphere (Forget et al., 2006; Head et al., 2006). Theatmospheric emplacement of ice/snow during the past higherobliquity excursions, which is the most favored scenario for accu-mulation and compaction of ice/snow, was observed to be mainlyfocused in individual alcoves within the plateau/crater walls orthey were deposited as kilometer-thick latitudinal scale cold-basedice sheets (Dickson et al., 2009a; Fastook et al., 2011). The intermit-tent ablation of these exposed or accumulated packs of ice/snowvia sublimation/localized melting have resulted in chronologicalformation of landforms that includes, (1) lobate debris aprons/lin-ear valley fills (LDA/LVF) (1 Ga100 Ma) (Levy et al., 2007;Morgan et al., 2009; Baker et al., 2010), (2) concentric crater fill(CCF) (30060 Ma) (Levy et al., 2010), (3) viscous flow feature(VFF) (300.1 Ma) (Milliken et al., 2003; Arfstrom andHartmann, 2005), and (4) young gullies/thermal contraction crackpolygon (TCP), etc. during the recent glacial epoch (2.10.4 Ma)(Head et al., 2003; Levy et al., 2009; Morgan et al., 2010). Theremarkable fact is that co-existing presence of all these conven-tional landforms has not been observed so far from a single cra-ter-like template or a confined region in the mid-latitude. Aunique combination of different types of features can lead to aholistic understanding of how exactly a terrain has formed or mod-ified while Mars was undergoing significant shifts in its climateduring the past (Kargel and Strom, 1992; Kargel, 2004). These land-forms are rather scattered and largely dependent on the orienta-tion of host surfaces, elevation of the terrain/crater on/in whichthey have formed, and its location in both the hemispheres(Dickson et al., 2007, 2012). As a function of latitude, they are dis-tributed, (1) mainly at the northwestern foot of the Tharsis andOlympus Mons (45) (Milkovich et al., 2006; Head and Marchant,2009; Dickson et al., 2012).

In mid-latitudes of both the hemispheres, Mars has alreadybeen shown to have preserved water ice in its subsurface as wellas experiencing controlled (seasons and obliquity) accumulationand compaction of ice/snow during the past (Head et al., 2003;Laskar et al., 2004; Forget et al., 2006; Holt et al., 2008; Plautet al., 2009). The modified form of impact craters in this regionof Mars would definitely demonstrate the collective influence ofgeomorphic processes, mostly the potential role of glaciation thathas contributed to their modification (Kumar et al., 2010). Theexact nature of relationships between the changes in the surfacemorphology of craters (rim, wall, central peak and floor) andchanges in the extent and style of glacial activities are still notentirely clear. Therefore, it becomes essential to demonstratethe sequential transition of martian surface while it was respond-ing to the periodic changes in obliquity and associated accumula-tion, flow and ablation of ice/snow. In view of this, we havechosen Moreux crater (135 km, centered at 41.66N, 44.44E)(Fig. 1) for identification of diagnostic signatures associated withspecific geomorphic processes and comparing the previouslyobserved glacial/periglacial features to what is observed for con-straining the relative importance of the recent and episodic gla-cial processes and their contribution to the modification of thecrater surfaces.2. Geological context and objective of study

Geomorphic signatures of ice-related flow have long been rec-ognized in the martian mid-latitudes and quoted as evidence forextensive glaciation (Carr and Schaber, 1977; Lucchitta, 1984;Kargel and Strom, 1992; Baker, 2001; Kargel, 2004; Head et al.,2006; Levy et al., 2007; Dickson et al., 2008; Baker et al., 2010;Sinha and Murty, 2013b). Moreux crater is among one of the larg-est craters in the DeuteronilusProtonilusNilosyrtis Mensae fret-ted terrain zone, where presence of subsurface ice and atmosphericaccumulation of ice/snow have already been reported (Plaut et al.,2009). The dichotomy boundary that divides the planet into twounequal halves is one of the most important geological and geo-physical constructs of ancient Mars (Wilhelms and Squyres,1984; McGill and Squyres, 1991; Sleep, 1994; Citron and Zhong,2012). Moreux crater has significantly modified this boundary asmore than half of its portion from south was superimposed onthe regional scarp. Perhaps the southern portion of Moreux rimin fact represents the dichotomy at that place (Fig. 1) and subse-quently the majority of pre-existing mesas that characterizes thedichotomy boundary along this region have been densely obliter-ated (Marchant et al., 2006). Only the western-most rim of Moreuxrepresents its actual rim in terms of its elevation at the time of for-mation, as from other three (NSE) sides it has unequal shape andelevations due to impact over a pre-existing undulated topogra-phy. The western rim that has maximum slope while trending fromtopbottom is elevated at height of 3 km from the floor of crater,whereas the other parts of the rim and floor are relatively undu-lated and are elevated at unequal heights from floor to rim(Fig. 2a and b). Along the southern portion of crater floor, near toits rim, there exists a large heap of deposited materials sourcedfrom the glacial valley at the head of rim. From all the other por-tions, several flow features that certainly bear a resemblance toflow of ice/snow rich materials in the form of channels and lobe-like impression are scattered over the surface at the proximity ofrim/wall. Otherwise, the crater floor is relatively less altered fromthe portions between the rim and central peak. At the central peak,the flanks and their margin are mostly surrounded by long andlarge lobate flows that appear to originate from the varying sizealcoves at the top of central peak. The 3 km tall original centralpeak and the proximal surface have undergone heavy modification,leaving behind cluster of multiple small-elevated mountains onwhich glacial flows have draped, folded and merged into largerlobes at flanks (Fig. 3). Overall, glacial folding/flow, channelizedflows from top of rim, incision of floor and rim by valleys, and flowof ice-rich debris from adjacent plateaus in the region appear asthe prime causes that have contributed in modification of the cra-ter surfaces over rim/wall and around central peak.

In this paper, we primarily aim to address the processes andextent of crater modification by the analysis of geomorphic signa-tures extracted from rim, wall, floor, and central peak of crater fordemonstrating the periodic changes (recent and episodic) in gla-cial/periglacial activities from past 1 Ga0.4 Ma (Fig. 4). A geo-morphic map was prepared based on identification of landformsassociated with ice-rich processes, which are then analyzed withMOLA topography to assess their downslope flow characteristicsand stratigraphic relationships. This has enabled us to assess theevidence for multiple shifts in martian climate that led to inducevariation for ice/snow accumulated during this period and their

Fig. 1. Location map showing major geographic features. Moreux crater is in the center of the figure displayed within the white box. Map shows the superposition of crateronto the dichotomy boundary escarpment (blue dashed line) between Protonilus Mensae and Ismeniae Fossae and its global location. Location of other features near Moreuxare labeled. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. (a and b) Mars Orbiter Laser Altimeter (MOLA) data displaying topographicvariations across NS and WE portions of crater. Transect of the profiles are shownin Fig. 4.

124 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144subsequent ablation. From the geomorphology of examined land-forms, we attempted to separate and classify the landforms thatbear implications for understanding the role of slow and fastresponse in climate change on the modification of craters. In thisprocess, we searched for those sites within the crater where youn-ger and older glacial/periglacial features were coexisting at thesame place. This has helped in constraining whether the surfacesthat have modified earlier were only prone for further modification(during 1 Ga0.4 Ma) or there were new sites that only modifiedlater (during the recent glacial epochs;

Fig. 3. Graphical representation of small-large mounds/blocks around central peak using MOLA gridded topographic data.

Fig. 4. CTX mosaic of Moreux crater displaying location of other figures in textshown as labeled boxes.

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 1254. Observations: geomorphic discrimination of Moreux units

Geomorphic discrimination of the landforms observed fromthe crater is important for our clear understanding of geologicevolution of the surface within the crater. The identificationof features and their relationships with terrestrial analogs fur-ther provide a basis on which to assess whether ice/snow waslikely to have reshaped the geomorphology of the post-impactcrater terrain. In this section, we provide geomorphic detail ofcrater to build on the importance of stratigraphic relationshipsamong different scale of features observed within Moreux incontext of inferring episodes of glaciation on Mars. For this pur-pose, a geomorphic map of Moreux was prepared for outliningthe distribution of important features possessing similarities toglacial features mapped elsewhere on Mars and on terrestrialglacial systems (Fig. 5). Different scale of glacial features weredelineated that includes LVF, LDA, VFF, lobate flow features,valleys, gullies and polygons at the rim, wall surface, andaround central peak of crater. The extents of LVF/LDA/VFF unitswere determined based on the texture of emplaced debris thattransformed into linearcircular ridges while flowing down-slope or draping around the obstacles in vicinity of crater wall.Around the central peak, we observed large-scale lobate flowfeatures flown from alcoves at the top of central peak whoseflow characteristics displayed typical similarities to lobesobserved near Surprise Fjord in the southern part of Axel Hei-berg Island, Canadian Arctic (79.80N, 91.20W). Features asso-ciated with recent phases of glacial modification (past 2.10.4 Ma, i.e. gullies and polygons) were observed and includedin the map based on their location within or around Moreux(Head et al., 2003). Another interesting example includes thepresence of a large valley breaching the southern portion ofcrater, sets of inverted valleys at the base of northern wall,and several smaller valleys, which rapidly bend along the slopeand merge to flow over the wall surface. At most places, theexistence of smaller valleys had been overprinted by the down-slope flow of eroded debris as well as most of them vanishedbefore converging over the floor. Regions associated with mod-ification processes (i.e. aeolian activity) that had formed dunesover the crater floor were outlined in mapping, but excludedfrom the analysis.

In two portions taken from northern and western part of Mor-eux using merged product of CTX and MOLA datasets, we couldobserve that LVF and LDA resulted from downslope flow of glacialice (Fig. 6a and b). The morphological analysis of the flow patternof these features helped in outlining many similarities to typicalcharacteristics shown by ridges formed by flow of ice mixed deb-ris in terrestrial valley glaciers. These include formation of ridgeswhile: (1) downslope flow of LVF controlled by obstacles, (2)downward exit of LVF between obstacles, (3) flow of LVF aroundor obstructed by obstacles, (4) flow of LVF within narrow spaceand depressions between obstacles, (5) emerging in linearcircu-lar patterns away from the base of massifs, (6) drape of LVF overtopographic obstacles, (7) folding and tightening alongside obsta-cles, and (8) opening, merging and broadening during obstacle-free flow over undulated wall-floor topography. Taken together,the presence of these types of features over the wall-floor surfacefurther highlight on the role of ice to induce different stages dur-ing which integrated glacial systems formed within Moreux; sim-ilar to the classical flow characteristics displayed by terrestrialdebris-covered glaciers (Barsch, 1971; Whalley, 1974). Further-more, analysis of lobate flow features around central peak of cra-ter emanating from alcoves and proximal massifs offered anopportunity to explore the intriguing flow patterns and theirinter-relationships with terrestrial lobate flow features. Weexpand the prior documentation of such lobate flow features fromour detailed analysis of these uniquely positioned features withinMoreux.

Fig. 5. Morphological map of study region based upon mosaic of CTX images. The multitude scales of landforms observed within Moreux are mapped along with changes inthe height of the surface over which they are emplaced. The red line contours are derived from MOLA gridded topographic data. (For interpretation of the references to colorin this figure key, the reader is referred to the web version of this article.)

126 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 1221445. Interpretation of landforms

5.1. Modification of central peak

Mapping of features around central peak (Fig. 7) of Moreux sug-gested that this portion presumably altered into small-largemounds/blocks by major and moderate accumulation of ice/snowresulting in integrated flow patterns larger than tens of km andmultiple LVF lobes. Of a more recent and less intense nature, fea-tures similar to gullies were observed from a small portion. Inte-grating the scale of observed features from central peak indicatesthat this region probably acted as the locus for accumulation ofice during the past, closely resembling the typical mid-latitude cra-ters with landforms of sequences as described below.

5.1.1. Coalesced flowsThe process of coalescing inmartian glacial landsystem has been

recognized as a key process in forming large valley glaciers thattend to emerge from merging of the growing LDAs, which formLVF-like textures while flowing down gradient (Carr and Schaber,1977; Kargel, 2004; Head et al., 2006, 2010). Coalescing of downslope flows are mainly observed at places where multiple alcove-fed flows flowing around obstacles, undergo folding, compression,and deform for longer distances, which terminate forming con-vex-up lobes at the base of the slope (Dickson et al., 2008, 2009a).From the portion of central peak investigated in this study, the coa-lesced flows were observed at the base of high-standing (3.0 km)peak of Moreux (Fig. 7a). The central peak originally consisted ofmultiple and varying size alcoves from where flow would haveemerged forming LDAs subsequent to ice/snow accumulation, ero-sion, and down gradient flow of debris. As the emerging LDAs grew,they coalesced, merged, and began to flow away from the centralpeak, down gradient with LVF-like textures on its surface, forminglarge and integrated glacial valley systems. The majority of coa-lesced flow features were observed at the southwestern end ofthe central peak that extended to 5 km from the base towardthe crater wall. Flow of debris along the base of central peak, in con-cert with sublimation of dirty ice, produced classic rock-glacier likecharacteristics (Wahrhaftig and Cox, 1959; Barsch, 1971, 1977;Whalley, 1974; Humlum, 1999; Whalley and Azizi, 2003; Kband Reichmuth, 2005; Giardino et al., 2010).5.1.2. Tributary debris-covered piedmont glacierIn terrestrial glacial systems, piedmont glaciers are often

observed at the base of mountain ranges as a rounded and flat gla-cier that likely resemble downslope spread out of debris from steepvalley glaciers into several integrated small-large C-V shaped lobes(Manohar, 2011). On Mars, piedmont lobes are formed when theturn and downslope flow of circumferential LDAs often merge withthose from neighboring massifs to create LVFs that extend, flowand spread downslope into significantly larger lowland(Milkovich et al., 2006). Piedmont-like lobes are more commonat places where extended flows of LDAs have encountered localdepressions. The large alcoves at the top of central peak of Moreux,during the period of higher spin/axis obliquity excursions experi-enced major accumulation of ice/snow, resulting in multiple top-down flows of ice-rich materials (Fig. 7b). The coeval flow anddeposition of ice-rich debris fed from alcove has spread compoundLVF lobes in the lowland region, which coalesced to form largepiedmont-like lobate terminations in the adjacent lowlands. Thetopographic profile of this piedmont-like flow feature maintainsa convex-up profile at the toe and display typical top-down flowcharacteristics similar to the profile of terrestrial debris coveredglacier flow. In the latter case, the topographic profile appears tobe uniform with limited changes in slope, whereas in the formercase the profile significantly lowers while approaching the erosion(E) zone and toward the transportation (T) zone. The past flow ofice along with debris from this martian alcove might have loweredthe surface topography of the lobe due to sublimation andenhanced slope-fed erosion. In the case of terrestrial glacier, theprofile indicates the surface topography of the top layer of the rockglacier plus the accumulated ice pack. It may be possible that theoverall flatness in the profile is due to uniformity in accumulatedice over the rock glacier beneath and caution has to be taken beforemisinterpreting it to indicate minor level of erosion. However, it isimportant to mention that in terrestrial glaciers sufficient lubrica-tion is provided to the debris while its downslope flow duringmelting of accumulated ice packs, whereas in case of Mars, accu-mulated ice packs underwent sublimation instead of melting. Itis expected that from loosening of debris along the slope and theirflow in absence of meltwater, an enhanced level of erosion mightbe active during the past that increased the level to which debriswere removed and emplaced at the base.

Fig. 6. (a and b) The merged products of CTX and MOLA (V.E.: 10) illustrate the relationships among components of downslope flow features observed within the studyregion. The flow pattern of these features display typical characteristics shown by ridges formed during flow of ice-mixed debris in terrestrial valley glaciers. The black andwhite downward oriented arrows in both the figures a and b shows the direction of flow of LVF materials.

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 1275.1.3. Superposed LVF lobeA similar lineated lobe has formed just to the east of piedmont-

like lobe, from flows emerging from a comparatively small alcovethat eroded, transported and deposited ice-rich materials downgradient into lobate terminations (Fig. 7c). In this case, emergenceof linear LDA formed LVF, which in turn coalesced to form lobe asthe LVF flowed downslope and out onto the surrounding plains.This lobe stratigraphically superimposes on the older coalescedflows and emphasizes on the importance of difference in periodand extent of ice/snow accumulation to produce such varying mor-phology. The flow of debris and formation of ridges in this case andin the interpreted terrestrial analogs are controlled by the topo-graphic obstacles aligned parallel to the direction of flow at boththe sides. Such an example of lobate flow within Moreux and onEarth strongly implicate that topographic obstacles played a keyrole in shaping the glacial geomorphology of terrains on Mars.5.1.4. Draped flowsConsistent with converging and diverging patterns of LDA and

LVF are draped flows that occur at the base of central peak, wheredifference in flow velocities caused draping of flow lineationsaround local blocks/mounds that opened in patterns resemblinglarge viscous flows. Such type of flows were facilitated by accumu-lation of ice/snow at the top of central peak that gained velocitieswhile traveling longer distance from topbottom, progressing withtightening and folding, forming larger tributary valleys containingcoalesced LVFs which originated from individual alcoves (Fig. 7d).The flow has terminated while extending and spreading up to theobstacles in the flat lowlands that progressively deformed fromzones originally rich in snow and ice, subsequently sublimatingand leaving combination of circular and elongated depressionson its surface. Such draped flow features clearly demonstratemajor late Amazonian glacial activity that involved considerablylarger amounts of glacial ice/snow producing numerous LVFs thathave modified major portions around central peak.5.1.5. GulliesSubsequent to the formation of alcove-fed LDA and LVF at several

portions of central peak, the major alcoves that facilitated accumu-lation of ice have undergonefine-scale erosion at their topmargin toform smaller alcoves at that place. During the most recent glacialepoch, i.e. 2.10.4 Ma, due to localized accumulation of ice/snowand their ablation via melting during extreme summer afternoonsled to formation of very narrow shortened gullies at those places

128 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144(Costard et al., 2002; Christensen, 2003; Head et al., 2003; Dicksonand Head, 2009). The gullies that have formed appear to have crosscutting relationships with the pre-existing fractures, implying pos-sible difference for glacial ice/snow accumulation controlled by pastspin/axis obliquity variations and climate changes (Fig. 7e (i)). Theobserved characteristics of these gullies do not match with thoseof typical martian gullies previously identified elsewhere and evendo not bear the traditional alcovechannelfan relationship (Fig. 7e(ii)) (Mangold et al., 2010;Morgan et al., 2010). Despite having asso-ciation among these morphological units (alcove, channel, and fan)in the gullies we observe here, they presumably seem to haveundergone fair erosion before they were left undisturbed (Fig. 7e(i and ii)). The likely resemblance of formation process to thosedefined in the previously published literature probably imply thatgullies observed here and elsewhere have indeed formed duringsimilar obliquity and climatic conditions that induced similar fash-ion of accumulation and ablation of glacial ice/snow (Costard et al.,2002; Christensen, 2003). The presence of gully-like features at thecentral peak of Moreux and the obvious superposition relationshipsamong other features lend support to our suggestion that the craterunderwent episodic modifications from the late Amazonian to therecent past.

5.2. Modification of rim/wall surfaces

Several questions remain in the understanding of the sequenceof crater modification with respect to changes in past spin/axisFig. 7. Region of interest around central peak of Moreux and location of other figures frextending from base of central peak of crater. Note the complex flow pattern of ice-richglacier-like characteristics. (b, i) A piedmont-like lobe around the central peak of crater aDistance is in arbitrary units. (b, ii) A similar piedmont-like lobe near Surprise Fjord in theGDEM profile extracted along topbottom of the lobe (A: accumulation zone; E: erosionwithin the gap between obstacles. The example of terrestrial LVF lobe is from a region neexample of drape of ice-related flows from the top of peak base while flowing along the spattern of flow while it drapes around the obstacle and extend into larger lowland, formdisplay evidence for accumulation of ice/snow over the surface of flow in form of large chprofile along AA0 was extracted using MOLA datasets. Distance is in arbitrary units. (e,Moreux that formed gullies around a small portion. Note the relation between older fraobliquity excursions and overall influence of climatic shifts thatform glacial/periglacial landforms over the rim and base of a craterwall. They are: (1) Is there a relation between climate evolution,topography and emplacement of LDA/LVF in multiple scales alongrim and wall of craters? (2) What is the proportion of ice remainingin the VFFs, which is regarded as best indicator for representingglacial action? (3) Had the accumulated packs of ice/snow everundergone melting and formed valley/channel even at elevationshigher than the interior of crater? (4) What were the scale, timingand duration of erosional processes and how they contributed inmodification and resurfacing of the crater? and (5) How the rateof response to martian paleoclimate conditions has controlled theformation of glacial/periglacial landforms? With the observationand analysis of glacial/periglacial features over rim/wall surfacesof Moreux and their interpretation in context of modification ofcrater, we aim to address these questions in the following sections.

5.2.1. Emergence of LDALDAs on Mars have been commonly perceived as having glacial

origin due to their consistent down-slope flow characteristics (Carrand Schaber, 1977; Squyres, 1979; Squyres and Carr, 1986; Kargeland Strom, 1992; Kargel, 2004; Baker et al., 2010; Head et al., 2006,2010; Hubbard et al., 2011; Sounness and Hubbard, 2012). Itevolves in linear and circumferential patterns from crater wallsand theater-shaped depressions of rim and terminates in lobateshaped pattern surrounding scarps and massif at the base of wall(Baker et al., 2010). LDAs within the Moreux bear major signifi-om this region shown as labeled boxes and dots. (a) Coalesced flows in the regionmaterials that formed multiple lobes while flowing down-gradient resembling rocknd the corresponding MOLA profile extracted from top-down of a section from lobe.southern part of Axel Heiberg Island, Canadian Arctic and the corresponding ASTERzone; T: transportation zone). Distance is in arbitrary units. (c) LVF lobes emergingar Surprise Fjord in the southern part of Axel Heiberg Island, Canadian Arctic. (d) Anteeper topography. The flow interacts with obstacles in the region that controls theing lobate terminations. The kettle-like morphology formed in the lower portions

unks that left hollows after sublimation of ice/snow from that place. The topographici and ii) Evidence for a relatively younger stage of glaciation around central peak ofctures in this region and fresh gullies that incised them while flowing topbottom.

Fig. 7 (continued)

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 129cance in modification of crater as multiple patterns of LDAs haveoriginated and deposited massive aprons at the base of wall, atmost from all the sides of rim. In the mapped region, numerouslocal alcoves seemed to be the source of multiple flows thatemerged away from the crater wall toward the floor resulting inLDA deposits (Fig. 8af) (see Fig. 9, for a closer view). The synthesesof these LDAs clearly indicate significant crater surface modifica-tion along the rim/wall in the following manner: (1) larger amountof ice/snow packs accumulated on crater wall or trapped into the-ater shaped depressions of rim during the late Amazonian, (2) abla-tion of ice/snow, erosion of debris, and the top-down layered flowfrom crater wall/rim similar to flow of debris covered glaciers(Fig. 10), (3) lateral to circular emergence of debris flow from theseportions that converged, folded and merged at the base of wall

Fig. 7 (continued)

130 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144(Fig. 10), (4) these LDAs underwent compression between obsta-cles and distorted while flowing down-gradient to form LVFs thatlater fed the regional LDA in the downstream region, and (5) theflow of LDAs from wall of crater lastly superimposed on the craterhost materials and resurfaced the exposed geologic assemblages.

5.2.2. Emplacement of LVFTheater shaped depressions in the wall of crater are common

locations fromwhere LVFs confined within topographic heads orig-inate in the form of narrow and long parallel ridges that resembletop-down flow of glacial ice mixed with debris during the lateAmazonian (Levy et al., 2007; Morgan et al., 2009; Baker et al.,2010). In general, LVF is emplaced away from the crater wall andit follows the local topographic gradient to create flow along thevalley (Fig. 11), where it undergoes complex folding and appar-ently terminate in tongue shaped lobes (Baker et al., 2010). WithinMoreux, LVFs derived from majority of alcoves within walls andmassifs rapidly deformed, compressed between obstacles in startof its way down gradient and evolved as complex narrower foldsto emplace integrated LVFs in the proximal parts of original LDAs(Fig. 12ai) (see Fig. 13 for close-up view). The unusual folds andcomplex divergingconverging flow patterns of LVFs suggested

Fig. 8. Examples of patterns of LDA emergence within Moreux. (a) Convergence of a LDA between topographic obstacles that stack up and hanged above an obstacle whileflowing down gradient to merge with regional LDA. (b) Linear LDA that eroded and incised an obstacle and flowed down gradient to merge with regional LDA. (c) Linearcircular emergence of LDAs from crater wall that formed lobe-shaped terminations with multiple flow-ridges on their surface. Note the erosion and modification of crater wallcaused by successive flows. (d) Linear LDAs emerging from flows along crater wall and converging within obstacles. (e) Drape of linear LDAs on obstacles that transitioned toLVF on extension of flow. (f) LDA merging and distorting down gradient to form patterns similar to LVF.

Fig. 9. Sketch map of the CTX image displaying an integrated flow emerging from alcoves in the northern wall of crater that compressed while flowing around obstacles andmerges with the main LDA as suggested by the downward continuity of the flow. The thick and fine lines represent the major and moderate flow ridges in the region.

Fig. 10. Sketch map of CTX image of top-down layered flow emerging from crater wall/rim similar to the flow characteristics of debris covered glaciers. The thick and finelines represent the major and moderate flow ridges in the region.

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 131

Fig. 11. Sketch map of the CTX image displaying example of a LVF emplaced away from the crater wall that follows the local topographic gradient to create lobate flow alongthe valley. The thick and fine lines represent the major and moderate flow ridges in the region.

Fig. 12. Examples of emergence of LVF from alcoves in wall of crater. (a and b) Flow of linear LDA that gets confined to the topographic obstacles on extension and form LVFlobe at the base. Note the similarity pattern of top-down flows. (c) Multiple flows from alcoves merge to form a single LVF that follows the steep slopes over which it drapesand form a single lobe with multiple flow ridges on its surface. (d) Merging of LDAs from different directions to form a single LVF lobe. (e) An example of multiple flows fromthe top of wall initially in form of LDA, which extends to form LVF and these LVF extends downslope to merge with and feed the regional LDA. (f) Typical example of a viscousLVF lobe originating from an alcove at the top of wall. Note the pattern of curvilinear flow ridges on the surface. (g) An example of LDA on interacting with an obstacle thatbends, widens, and extends the flow over a steeper topography. (h) Convergence of bidirectional flows between obstacles to form a LVF lobe. (i) Flow of curvilinear LDAs thatextend to form typical moraine characteristics such as loop, bending and outflow on interaction with flow from adjacent alcoves and obstacle.

132 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144that their formation involved significant ice, which later termi-nated close to the rim and wall, forming lobe shaped fronts. Thetopographic profile of these LVF features corresponds to simpleprofiles with their typical top-down movement aided by the grad-ual changes in slope (Fig. 14ac). The examples of topographic pro-files include LVFs showing flow over obstacle, convergence of flowfrom multiple massifs to singular lobate front, and flow betweenobstacles. These profiles and the consistent lobate shapes of LVFs

Fig. 13. Sketch of CTX image displaying downslope flow of LVF away from the crater wall, compressed between obstacles, which evolved as complex narrower folds toemplace integrated LVF in vicinity of the main LDA. The thick and fine lines represent the major and moderate flow ridges in the region.

Fig. 14. (a and b) MOLA based topographic profiles of LVF features displaying typical top-down flow aided by the gradual changes in slope. Distance is in arbitrary units.

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 133confirm that they were derived from top-down flow of debris fromthe massif. The overall absence of superimposed impact craters onthe surface of LVF hinted that the deformation of these features hasbeen minimal within Moreux since their emplacement, implicatingit as a prime candidate for modification of craters surface. Anotherpoint to ponder for absence of craters over LVF surface could beepisodic modification by flow of viscous ice-rich materials overthe LVF surface during the period of less extensive glaciation.Therefore, whatever craters currently remain intact on the surfaceof LVF may have formed later to the modifications by viscous flowfeatures. Such evidence takes us closer to our argument that Mor-eux could be that geologic template where the key morphologiesdeveloped during most of the recent and episodic glacial events(1 Ga0.4 Ma) could be perceived.

5.2.3. Viscous glacial-flow featuresSimilar to the large-scale flow features, such as LDA/LVF; VFFs

on Mars have characteristics including surface lineations, compres-sional ridges and flow fronts that implicate flow of near surface icein their formation (Milliken et al., 2003; Arfstrom and Hartmann,2005). The VFFs generally bear a relatively smoother texture sur-face on which it is superimposed. They consist of linear to circularflow ridges following the steeper topography, primary and second-ary tongue shaped lobate fronts, and tend to undergo compressionor extension while flowing over or around the obstacles. Com-monly, a distinct boundary divides the constructed VFF from theadjacent material that appears to be stratigraphically lower thanthe VFF flow ridges. Moreux hosts classical small-scale glacier-likeflow features that apparently resemble VFFs observed elsewhereon Mars (Fig. 15af). The observed VFFs consist of primary and sec-ondary lobes, confined within rigid and thick frontal ridges thathosts multiple compressional and extensional ridge on its surface.In addition to these small scale VFFs, we observed evidence for alarge-scale (16 km long and 6 km width) viscous flow featurealong the southern rim of crater (Fig. 16). The flow appeared tobe much larger than initially flowed, away from the crater wall,while draping over it and spread as a large flat lobe on the craterfloor. The emplaced lobe uniquely consists of multiple linearcir-cular narrower sublimated faces, which could be an indicationfor some amount of ice still being present beneath these VFFs.

Fig. 15. (af) Examples of VFFs within Moreux crater that resemble typical top-down flow characteristics and terminate in lobe-shaped fronts while flowing around obstacles.Note the pattern of flow, perseverance of these morphologies within Moreux, and presence of extensional and compressional ridges on the surface of VFFs.

Fig. 16. An example of a large VFF in southern portion of crater. Note the presenceof sublimated units on the surface of VFF that helps substantiate that these featuresstill contain an amount of ice/snow preserved beneath a lag deposit.

134 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 1221445.2.4. Valley networksOn Mars, the mid-late Amazonian has had a prevailing climate

where the mean annual temperature has been far below the triplepoint, wherein liquid water has primarily not been stable onthe surface (Ingersoll, 1970; Costard et al., 2002). There have beenanomalous conditions when liquid water has been stable and mayremain stable, but these anomalies pertain to special locations atspecial latitudes and elevations and particular phases of theobliquity cycle, or for special aqueous chemical solutions (Clow,1987; Haberle et al., 2001; Hecht, 2002; Laskar et al., 2004; Toscaand McLennan, 2006; Dickson et al., 2007, 2009a, 2009b;Marion and Kargel, 2008; Williams et al., 2009; Kereszturi andRivera-Valentin, 2012; Marion et al., 2009, 2013; Martnez et al.,2013). Therefore, the mechanisms and the associated environ-ments for the formation of valley networks remain discontented.However, it has been the consensus by a large group of scientiststhat water in some way has played a key role in the formation ofmost of the valleys (Gulick, 2001; Craddock and Howard, 2002;Hynek and Phillips, 2003; Howard et al., 2005; Ansan andMangold, 2006; Hynek et al., 2010). This is despite the fact thatthe present environment or of the recent past had been adversefor allowing water to flow downhill as streams. Beyond this, therehave been several times when possible flow of water without con-necting it to the processes relying on environmental conditionshave been accounted (Newsom, 1980; Brakenridge et al., 1985;Clow, 1987; Gulick, 1998; Malin and Carr, 1999; Fassett andHead, 2008; Jones et al., 2011; Mangold, 2012; Kite and Manga,2012). Among them, one of the scenarios seeks to describe thepossible formation of valley networks by flowing water whileimplicating impact-heat related hydrothermal activity to aid inmelting of ice and flow of meltwater (Newsom, 1980; Joneset al., 2011; Mangold, 2012). From Moreux, something what weknow for sure is that ice has accumulated at nearly all the facesof wall and at/around central peak, and by looking at the multitudescale and variety of landforms it is also worth emphasizing thatMoreux had experienced extensive ice accumulation over itssurface for a long lasting period.

In Moreux, the small valleys, typically 20200 m deep and50300 m wide, consistently narrowed at the end, with numeroustributaries, occur mostly on the wall of the crater. These valleystypically extend from below the rim crest; however, in somecases the flow is from the top of rim. From our observations,we found that these valleys are distinctly associated withthe suite of glacial features (such as LVF/LDA/VFF) found withinthe crater (Fig. 17). At all the places where valley and LVF/LDA

Fig. 17. Sketch map of CTX image illustrating associations between valley extending from top of the rim with the LVF flows at the base of wall. The dashed line represents theridges over LVF surface.

Fig. 18. (a and b) Examples of valley networks within Moreux crater. Both the images display randomly distributed complex valley network systems and superpositionrelationships among valleys and LVF/LDA features.

Fig. 19. Sketch map of CTX image showing a set of confined valleys at the base of northern portion of wall that underwent filling at a later stage by the LVF materials. Furtheraeolian erosion of the valleys resulted in impressions similar to inverted valleys on Mars.

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 135are in stratigraphy, the valleys are superimposed by LVF/LDA(Fig. 18a). Most of the valleys have been filled as they reach thesurface level from where LVF/LDA started to form and in somecases when valleys have reached near to the floor, they have beenmasked by downslope flow of debris from top (Fig. 18b). In anotherexample, we could observe that a set of confined valley underwentinfilling by the LVF materials, which was further modified by aeo-lian erosional processes to give impressions similar to the invertedvalleys on Mars (Fig. 19) (Williams et al., 2009). What is clear fornow is that these valleys formed earlier to the formation of LVF/LDA during the late Amazonian history of Mars. Furthermore,although the width and depth of these valleys are not largeenough, the length of these valleys are substantially large, extend-ing up to tens of km from the rim. The water that might have flownhad at least a fair length of run within the crater than it could erodethe underlying surface. Such a long run of flowing water on Mars isexpected to be possible under an insulating layer that protected itto loss from evaporation. As on its exposure to the air, it will beginto simultaneously boil and freeze (Conway et al., 2011). Analysis ofcertain conspicuous valley networks and drainage patterns withinMoreux sometimes indicate that heat generated by the impact pro-cess might have melted the accumulated ice/snow to flow down-slope. However, within the crater we do not see any pervasivesignature of igneous activity as well as if there was any persistenteffect of heat followed by impact, the valleys should be more con-centrated near the central peak than the rim/wall (Barnhart et al.,

Fig. 20. (a) CTX mosaic of the eastern portion of the crater demonstrating the breach of crater wall/rim from southeast portion by flow of LVF materials from the adjacentmassifs. The breach of rim has deposited large amount of LVF materials over the floor of Moreux thus resurfacing the crater surfaces. (b) Mosaic of nighttime THEMIS IRimages of the same portion of the crater. The THEMIS datasets display difference in the thermal properties of the LVF materials and adjacent massifs outlining the flow. Therelatively darker pixels of LVF materials from that of massif correlates to low thermal inertia and temperature, which we interpret to represent relatively finer materials in theLVF materials to that which comprises the massif. Letters a and b in (a) represents locations of the features shown in Fig. 21a and b.

Fig. 21. Evidence for brain-terrain like texture from surface of LVF materials flown from the mesas shown in Fig. 20a and b. Brain-terrain like features are generally anoutcome of enhanced induced thermal stress, contraction and sublimation over LVF deposits. The locations of both the figures are highlighted in Fig. 20a.

Fig. 22. MOLA based topographic profile of the surface over which LVF materialseroded from adjacent mesas flown inside the crater. Note the absence of anysignificant obstacles in the overall path over which the flow has taken place.Transect of the profile is shown in Fig. 20a (AA0). Distance is in arbitrary units.

136 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 1221442010). Additionally, if the ejected materials had to act as heatsource for the melting of initially available ice deposits, then thevalleys had to be present outside the crater than being present overthe rim/wall surfaces. It is also worth emphasizing that the maxi-mum formation age of LVF/LDA or any potential glacial landformonMars is1 Ga, which shows a major time lag between the craterformation age (1.31 Ga) and the time of accumulation of ice toform such valleys. However, if substantial amounts of ice were ini-tially present, either out/near the rim or beneath it, then possiblehydrothermal activity or at least formation of gully-like channelscould have taken place on interaction of ice with warmed rockon the crater floor and in the walls. Nonetheless, from our exten-sive survey of glacial/periglacial features over/around the wall/rim of crater we could not extract any such evidences. Thus, thisprovides a significant support for our assumptions that impactheating might not be responsible for the formation of valleynetwork at least within Moreux. Perhaps, it is very complicatedto tag a single process that can explain formation of bulk of thesevalley networks observed at different locations on Mars. In order toexplain formation of valleys within Moreux we envisage thefollowing scenario: (1) ice/snow started to accumulate over therim/wall of crater as well as outside the rim during the early stagesof an extensive glaciation period, (2) the accumulation during thatperiod led to assimilation of regionally extensive layer of ice/snowover those surfaces (Kargel and Strom, 1992; Kargel et al., 1995;Head et al., 2003), (3) any amount of meltwater generated frommelting of ice at the top of this layer would have evaporated read-ily from boiling (Conway et al., 2011); however, some may havesurvived that generated from melting beneath this thick ice layer(Hobley et al., 2014), (4) its the weight of the overlying ice layerthat guided in downslope flow of meltwater that plausibly formedbeneath the ice layer during a pressure-melting scenario, and (5) as

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 137the valley progressed downslope, it narrowed, shortened, and itsdepth decreased. This is supported from our observations thatthe floor of crater does not show any pervasive glacial feature,which possibly corresponds to a less extensive layer of ice overthe surfaces away from rim/wall that was insufficient to exertthe required pressure to melt the ice. However, it is yet to be clearon how much was the required pressure to melt the ice beneaththe regional layer. It is important to mention that our explanationsare limited to our best possible understanding of the supportingclimatic environment inferred from published literature, andgeomorphic impressions and stratigraphic relationships extractedfrom the images.

5.2.5. Erosional featuresAlthough formation of glacial/periglacial landforms involve ero-

sion of the landscape on which they originate, an additional evi-dence that indicate major erosion of crater rim was observed(Fig. 20a). From a set of massifs lying in the northeast portion ofthe crater, it was observed that a large amount of LVF materialshave flown inside the crater while breaching the rim of crater.The surface textures of the LVF material show distinct presenceof brain-terrain like features as seen from MOC (1.512 m/pixel)and HiRISE (2550 cm/pixel) images (Fig. 21a and b). The presenceof brain-terrain features is commonly seen over the surface of LVF/LDA/CCF in other regions of Mars, which could be indirectly used asa proxy to confirm that the flown materials are glacial in origin(Levy et al., 2010). In addition to this, the LVF materials also showdifferent thermal properties in THEMIS IR mosaics than the adja-cent massifs lying along the sides (Fig. 20b). The massif-pixelsare brighter than the pixels of LVF materials indicating relativelyhigher nighttime temperatures, which also correspond to higherthermal inertia than that of the LVF materials flown toward thecrater (Christensen, 2003). This difference in the thermal propertycould be correlated to interpret the grain size of LVF materials,implying that LVF materials represent relatively finer material tothat which comprises the massifs (Christensen, 2003; Morganet al., 2009). Furthermore, the elevation difference between theupper limit and the crater rim is sufficient to direct the downwasted materials toward the rim, as well as the lateral down-valleycontaining the LVF materials is an obstacle free zone to provide anFig. 23. Example of polygons in a small portion within Moreux crater. Note the rigidand crisp nature of polygons that have formed, which indicates presence of ice/snow in the substrate during the past.unobstructed flow in that region (Fig. 22). Consistent with thisobstacle-free flow of eroded materials and general lowering of sur-face toward the rim has resulted in extensive breaching of the rimaffecting at least 10 km2 of the rim area. The rim has been trans-formed subsequent to its erosion into two large cliffs of 4 and2 km separated by a distance of 6 km between each other.There also exists an evidence for presence of large amount of sed-iments driven from the adjacent massifs lying over the floor of cra-ter at the vicinity of the eroded portion. This observation suggeststhat late Amazonian glaciation that produced majority of LDA/LVFin this region possibly invoked large amount of glacial erosion ofthe craters outside to which highstand massifs and related flowsare existing.

5.2.6. Polygons and cracksPolygons have been best utilized in previous work for demon-

strating climate-driven morphological evolution of the surfaceand for understanding the substrate properties, depth and contentof subsurface ice (Levy et al., 2008). The identification of thermalcontraction crack polygons across mid-latitudes in both the hemi-spheres of Mars has strengthened the evidence for presence ofshallow ground ice that eventually evolved to indicate vital cli-matic shifts within the past 2.10.4 Ma (Levy et al., 2008,2009). In consonance with the general fracturing of the terrainguided by series of thawingfreezing processes or sublimation, ina localized manner, the terrain has been significantly lowered withhigh marginal troughs, carved and reworked. Analysis of the topmost portions lying outside the northern rim of crater has revealedthe presence of well-developed polygons with marginal troughsthat randomly vary in its size and geometry throughout that region(Fig. 23). We could identify at least two classes among the poly-gons from those identified by Levy et al. (2009) in their global sur-vey of mid-higher latitudes for detection of polygons. They are: (1)high relief large (4050 m) polygons, and (2) flat top small (510 m) polygons. A sharp delineation of transition of characteristicsamong small and large polygons was not observed and larger poly-gons self-contained further smaller polygons bounded by relativelysmaller marginal troughs. The coexisting presence of these multiscale glacial/periglacial features within Moreux belonging to differ-ent time scales of late Amazonian martian history lend strongFig. 24. Expanded view of slumped deposits from the valley in the southern portionof Moreux. The deposit has ruptured into two unequal halves on change in theoverall slope as it flowed from wall toward floor. This has led to form typical crackssimilar to crevasses in the terrestrial glaciers. Note that the regional LDAssuperimpose these large deposits.

138 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144support to our argument that Moreux was certainly reworked by aseries of episodic and recent glacial processes.5.3. Modification of floor

We have analyzed the emplaced deposits and LVF materialsfrom the valley located around southern portion of crater and fromthe breached rim to highlight on the extents of floor modificationand resurfacing. Apart from these features, almost half of the por-tion of floor between central peak and rim/wall landforms have notshown any sign of pervasive resurfacing from glacial-like flows andeven seem to have survived refolding of terrain from glacial activ-ities. It was observed that due to prevailing wind action around thehigh standing central peak this region is densely covered with darkdune material (Cardinale and Komatsu, 2010).5.3.1. Valley and erosional depositsOne of the most interesting features along the southern portion

of Moreux rim was a large valley that incised more than 3 km ofthe rim and slumped large ice-rich materials on the floor of the cra-ter (Fig. 24). This large scale slumping provides a handle to estab-lish strong time-relation between the formation of LDA/LVF withinMoreux as it is observed that the emerged LDAs have superim-posed on the slumped materials. The deposit overlaps more than200 km2 of the craters floor with surface texture varying from asmooth terrain to cracks of width ranging within 10400 m. Theplanimetric view of the deposited materials present a divide thatdistributes the deposit into nearly two equal halves. The half por-tion near to the crater wall appears to have a smoother surfacewith very narrow random fractures whereas the other half has sub-merged on the steeper side, while being away from wall towardthe center. The portion away from wall consists of large fracturesthat typically resemble crevasses in terrestrial glacier landsystem.Probably due to relatively faster slumping of materials over theundulated floor, fractures resulted in the portion that was laid overa rather steeper portion of the floor, or it may be the effect of sub-limation to which the surface cracked on losing the ice from it.

Another layer of eroded materials spread over the floor of Mor-eux is visible in the northeast portion (Fig. 20a). The adjacentFig. 25. (a) Map of the crater-counting area on the adjacent plateau. The area of the counfor the age of the crater from count of 1894 craters over the surface of adjacent plateauhistory of Mars.mesas lying northeast of crater floor in that portion have alreadybeen demonstrated to breach a larger portion of Moreux wall inresponse to the flow of LVF materials from the mesas. This breach-ing of rim as well as flow of debris from adjacent mesa toward thecrater has eventually resulted in accumulating LVF materials over alarge portion of the crater floor. Extensive amount of materialswith rough/knobby surface texture have flowed along the steeptopography that overprint a large portion of crater floor. Therough/knobby surface textures of these materials reveal distinctpresence of brain-terrain like features (Fig. 21a and b). The pres-ence of brain-terrain corresponds to onset of an effect that inducedthermal stress, contraction and sublimation of the LVF depositsduring the past 10 Ma (Levy et al., 2009). An important fact thatemerges from this observation is that the overall surfaces ofemplaced materials originated from adjacent mesas, bear compar-atively lesser number of craters than on the preexisting floor ofMoreux, assigning a younger age to the superimposed LVF materi-als and the glacial processes. This helped us to establish that Mor-eux impact predates the formation of mesa/LDA/LVF in that regionand the major processes responsible for modification along thisregion is the episodic glacial action that prevailed through thosemesas.6. Crater sizefrequency distribution results

6.1. Age of Moreux crater

In the mid-latitude of Mars, various scales of glacial/periglaciallandforms resulting from multiple episodes of glacial activity sug-gest that the climatic conditions were suitable for multiple timesfor formation of debris covered glacier and flow of ice-related fea-tures during the past 1 Ga0.4 Ma. Marchant et al. (2006) haveobserved that in the north and south of Moreux, ejecta from theimpact can be identified on the summits of plateau and on the pla-teau, whereas in all other places across/within the crater LDA/LVFevidently postdate the ejecta. Concurrent to this we also observedthat the integrated flow patterns of LDA/LVF and other ice-relatedfeatures have clearly superimposed on the craters wall and floor.Of more significance is the transport of sediments from adjacentt surface is 3587.3401 km2. Background is THEMIS VIS datasets. (b) Crater count plot. The 1.31 Ga age of Moreux corresponds to its formation during mid-Amazonian

Table 1Age estimates of glacial features on Mars reported in literature and for the LVF/LDA/VFF features observed within Moreux. Note that the age of glacial features dependsignificantly on extent of erosional and depositional activities during different episodes of glaciation.

Landform Location Description Estimated age Principle Chronology Reference

LVF/LDA North of IsmeniaeFossae

LVF/LDA surrounding two largeplateaus

Best fit age of90 Ma

Count of all craters on allLVF/LDA surface

Hartmann (2005) Baker et al.(2010)

LVF/LDA DeuteronilusProtonilus Mensae

LVF/LDA in vicinity of Sintoncrater

>100500 Ma Count of all identifiablecraters >100 m

Hartmann (2005) Morganet al. (2009)

LVF/LDA Nilosyrtis Mensae LVF/LDA in northwest of ArabiaTerra

100 Ma1 Ga Count of craters >250 m overregional LVF

Hartmann (2005) Levy et al.(2007)

Piedmontlobes

Olympus Mons Lobate deposits at the base ofOlympus Mons scarp

130280 Ma Count of craters on majorlobes

Hartmann and Neukum(2001)

Neukumet al. (2004)

CCF Northern mid-latitudes

Concentrically-lineated, crater-filling deposits

60300 Ma Crater counts on ejectablankets of filled and unfilledcraters

Hartmann (2005) Levy et al.(2010)

VFF Northern andSouthernhemispheres

Glacier-like features withmoraine-like ridges

8 Ma Craters counted on surface ofa LDT

Hartmann (2005) Morganet al. (2011)

TCP Between 30 and 80in both thehemispheres

Latitude dependent mantlesurface patterned by polygons

1.5 Ma Count of craters on latitude-dependent mantle surfaces

Hartmann (2005) Levy et al.(2009)

Gullies Noachis Terra Gullies on pole-facing slopeswithin the Asimov crater

0.52.1 Ma Based on predicted values ofsurface temperatures overpole-facing slopes

1D version of theLaboratoire deMtorologieDynamique GCM

Morganet al. (2010)

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 139mesas in the northeast portion of the crater that has breached anddeposited large amount of LVF materials over the crater floor. Thisindicates that glacial activities from these mesas have not takenplace before Moreux impact, suggesting Moreux to have formedat least before 1 Ga. However, unless the crater is not stampedby counting the impact craters over an undisturbed region adja-cent to it, it is difficult to relate the superposition relationshipsamong landforms and ages for glacial/non glacial activities toderive the age of crater. Thus, in order to determine an upper ageboundary that marks the maximum potential age of the crater,we have measured the crater distribution over a proximal massiflying over southwest of Moreux. An outline of the area where cra-ters were counted and plot of the crater sizefrequency distribu-tion is given in Fig. 25a and b. From the landform evidences, wehave already demonstrated that this crater has substantially pre-served glacial/periglacial features that formed during the 1 Ga0.4 Ma history. Data from the crater sizefrequency distributionplot suggest that the Moreux impact occurred in the mid-Amazo-nian (1.31 Ga), coinciding with our discussions that the impactpredates the period of LVF/LDA formation on Mars. Such a config-uration for the age of crater thus qualifies to host landforms result-ing from majormoderateminor periods of glacial activities onMars.Fig. 26. Plot of the crater-size frequency distribution for all the craters (232)observed on all LVF/LDA/VFF surfaces mapped within the crater. Comparison withHartmann (2005) yields a best possible age of 1530 Ma. Since, formation of VFFover the LVF/LDA surface during a later, less extensive glacial phase has modifiedthe crater emplaced over the surfaces of LVF/LDA; this age is best applicable for theformation age of VFF within the crater.6.2. Age of glacial landforms

To address the question of timing of the glacial landforms, wehave counted craters on all the surface of LVF/LDA/VFF delineatedin the geomorphic map (Fig. 5). Within Moreux, we have identifieda multitude of distinct scales of ice/snow related landforms. Whentaken together, these landforms point toward distinct set of obliq-uity parameters, insolation and climatic conditions for their forma-

140 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144tion. For example, mapping of LVF/LDA in other regions of Marsand count of craters on their surfaces have suggested their periodof formation to be different from time-scales during which polygonand gullies have formed (Levy et al., 2007, 2009; Morgan et al.,2009, 2010; Baker et al., 2010). This is also consistent with ourunderstanding that LVF/LDA is compatible with periods of excesssnowfall, accumulation and flow of ice-rich deposits during periodsof higher obliquity, whereas gullies are a resultant of minor accu-mulation and snowmelt occurred during periods of moderateobliquity in the recent past (Head et al., 2008; Morgan et al.,2011). The landforms mapped within Moreux have been observedin different regions of Mars in the previous studies and simulta-neously formation ages of these landforms have been estimated(Table 1). The key is that Moreux holds evidence for presence ofall those glacial landforms that has been at least once observedin different glaciated regions on Mars. To estimate age of cratersurfaces occupied by LVF/LDA/VFF, we have counted all the possi-ble craters that were visible on their surface. As Moreux landformsprovide evidence for recent as well as episodic events of glaciation,the craters formed on the surface of LVF/LDA were modified by theformation of viscous flow features consistent with a later, rela-tively less extensive glaciation in the region. According toHartmann (2005) production function, the craters counted on allmapped LVF/LDA/VFF surface yield best possible age of 1530 Ma (Fig. 26). The younger age for surfaces combining LVF/LDAwith VFF could be possibly related to provide evidence for multipleglacial episodes within the crater (Baker et al., 2010). It is possiblethat the post-LVF/LDA glacial activities, consistent with a lessextensive glaciation in the region, emplaced relatively young lobeswith multiple parallelconcentric lineations over the regional LVF/LDA (Baker et al., 2010). Therefore, the age estimated from the cra-ter size bins is assumed to best represent the age for viscous flowactivities in the crater. Nevertheless, the 1530 Ma age for all cra-ter groups on all mapped LVF/LDA/VFF units is consistent with theages derived for other glacial-like VFFs mapped in mid-latitudes ofnorthern and southern hemisphere (Milliken et al., 2003).7. Discussions

From the morphological observations demonstrated in the pre-vious sections, we can suggest that formation of glacial/periglacialfeatures over the rim/wall surface and around central peak of thiscrater played a major role in its modification. Knowing that ice/snow accumulation was prevalent during the past 1 Ga0.4 Ma,we can confidently envisage that the periodic accumulation andablation of ice/snow within and around Moreux resulted in forma-tion of multi-scale glacial/periglacial features. In the following sec-tions, we discuss the major implications of our study for improvingour understanding of ice-related processes recorded within Mor-eux and their relationships with past climate shifts, and takingtogether, for emphasizing upon the fact that they lead to periodicmodification of the crater surfaces.7.1. Evidences for shifts in climate: oldestolderyounger glacialfeatures

Having briefly outlined the morphological characteristics ofsmall-large landforms observed within Moreux, it is now essentialto document the relationships between periods of past climatechanges and observed ice-related landforms for highlighting onthe climatic shifts. On Mars, the multiple shifts in mid-latitude cli-mate or episodes of valley glacier activity has been demonstratedbased on the documentation of stratigraphic relationships betweensmall-large scale ice-related flow features (Levy et al., 2007; Raacket al., 2011; Sinha and Murty, 2013a). Regional surveys of differentscale of mid-latitude glacier-like features have suggested that theextent of flow of these features were largely controlled by the sur-face topography and the amount of accumulated ice/snow(Dickson et al., 2007; Sinha and Murty, 2013a). The accumulationof ice/snow was mainly dependent on the spin/axis obliquity vari-ations during the past and the changes in climate have controlledthe removal of this either by sublimation or by localized melting,contributing to their formation at different scales. Since glacialactivities in the mid-latitudes of Mars was extensive during theLate Amazonian (1 Ga0.4 Ma), we are interested to decipherand present the evidences for shifts in climate for the undocu-mented Moreux crater during this period.

The glacier-like features (LDA/LVF/CCF/piedmont lobes) thattend to have large-scale integrated pattern extending for tens tohundreds of kilometers and their surface ages in excess of1 Ga60 Ma are interpreted to be related to a period when therewas major accumulation and ablation of ice/snow (Neukum et al.,2004; Levy et al., 2007, 2010; Morgan et al., 2009; Baker et al.,2010). The moderate phase of glaciation on Mars (300.1 Ma) isinterpreted to have occurred in a climate compatible with accumu-lation and ablation of ice/snow marginally above the requiredthreshold that formed landforms similar to VFFs (Milliken et al.,2003; Arfstrom and Hartmann, 2005). Under conditions duringthe last few million years (2.10.4 Ma), which likely yielded rel-atively small-scale flow features (similar to gullies, polygons, etc.),it is interpreted that the obliquity variations and climate haveresulted in localized and minor accumulation/ablation of ice(Head et al., 2003, 2008; Levy et al., 2009; Morgan et al., 2010).Taken together, the glacial/periglacial landforms, age, scale andstratigraphic relationships and the predictions from climate mod-eling attempts lend strong support to suggest that certain multipleshifts in the climate may have occurred over the last tens to hun-dreds of millions of years of martian history.

Among the oldest glacial/periglacial features, Moreux holds evi-dence for emergence and emplacement of large-scale of LDAs andLVFs from rim and wall of the crater (Figs. 8af and 12ai). There isevidence for large-scale erosional action resulting in removal oflarge portion of rim, breaching it, and initiating deposition over lar-ger portion of the floor (Fig. 20a). The ice-related flow features atthe base of central peak demonstrate how extensive the glaciationmay have been at that stage so we observed large integrated pat-tern of debris flow that draped, folded, and compressed before ter-minating with convex upward lobe-shaped fronts (Fig. 7b and e).Further evidence of regional reduction in the accumulation andablation of ice/snow or glacial action includes the presence of VFFsthat were observed in consensus to the LVFs over and at the base ofwall of the crater (Fig. 15af). Inspection of VFFs revealed charac-teristics similar to those of LVFs; however, there was apparentchange in the scale of these features. The flow pattern of VFFs wererelatively less complex and integrated, of smaller size and extent,as well as were found superimposed over the surface of regionalLVF, since the emplacement of VFFs were at a different time periodin the martian history (Fig. 15af). We interpret the apparentchange in the pattern of LVF and VFF as further reduction in theaccumulation of ice/snow into relatively smaller alcoves and con-sequent decrease in the level of sublimation and deflation thatindirectly helps us to focus on distinguishing the shifts in the cli-mate as evidence of transition from major to moderate period ofglacial activity. The recent glacial period on Mars is one of thewell-studied events (Head et al., 2008; Dickson and Head, 2009;Morgan et al., 2010), since this has made it possible to interpretand learn the build-up of the most recent climate developmentof Mars. The onset and culmination of this recent glacial periodhas emplaced landforms analogous to terrestrial gullies beingreferred to a period on Mars when accumulated ice/snow packshave undergone sufficient melting (Costard et al., 2002;

R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144 141Christensen, 2003) (Fig. 7e (i and ii)). This even involved formationof complex pattern of closed network of cracks termed as polygons,which is being attributed to patterned sublimation of the ice/snowfrom an unstable surface devoid of lag deposits (Levy et al., 2008)(Fig. 23). Understanding the amount of ice/snow involved in theformation of these glacial/periglacial features and the formationmechanisms are essential to interpret the difference in climaticconditions under which these features have formed. Nonetheless,it is well known from the previous studies that formation of thesesmall-scale ice-rich features on Mars was prevalent during themost recent phase of high obliquity (Costard et al., 2002; Headet al., 2003; Laskar et al., 2004). We interpret the observed changesin morphology as a certain shift in the climate of Mars that transi-tioned from a period of moderate accumulation and formation ofice-related VFFs to a period of minor accumulation and ablationvia sublimation/or melting and formed polygons and gullies duringthat time. Contrasting to these glacial/periglacial features and theirrelative times of formation, we have also observed dense networkof conspicuous valleys around many portions within and outsidethe Moreux crater (Fig. 18a and b). Based on the superposition rela-tionships, pattern, and width, we have interpreted that their originbelongs to a period when the overlying ice layer has induced pres-sure-based melting of the ice layer beneath, which then has flowndownslope to form such valleys. The uncontrolled formations ofthese channels may not relate with the heat aided by the impact;however, a regional climate change during that time in the historymight have played a substantial role in their formation (Hobleyet al., 2014). Based on comparison of observed landforms withinMoreux to similar landforms observed elsewhere on Mars andfrom previous attempts of climate modeling and estimating ageof these features via count of craters on their surface, our presentresults suggest that multiple phases of climatic shifts haveoccurred on Mars during the late Amazonian to the recent glacialperiods (1 Ga0.4 Ma) of Mars.

7.2. Effect of slow and fast response of climate change

Glacier land systems on Earth as well as on Mars have longserved as excellent indicators of climate change because variationin climate controls the accumulation and ablation of ice causingglaciers to advance or retreat. The continued monitoring of glacialsystems have helped in inferring short as well as long term climaticvariation at a regional or global scale because of their distributionin latitudinal location and different extents. In this attempt, weused our observations within Moreux to infer the effect of slowand fast changes in climate on local and regional build up of thesedifferent morphological features. This could be established onunderstanding the past spin/axis variations that involved accumu-lation of required amount of ice/snow to produce such morphologyand the time-frame during which the onset and completion of for-mation would have taken place during the past in martian history.We are aware that the actual examination of climate responseinvolves wide range of radiative forcings, including changes ofsolar irradiance, atmospheric influences, clouds, aerosols, surfacealbedo, surface elevation differences, and other spatial and tempo-ral parameters (Hansen et al., 1997). However, the type of datasetsutilized in this study can only give a plausible explanation to theseeffects while linking the explanations to the morphological obser-vations. From the previous studies carried out in view of preparingrobust climate models/GCM, it is understood that the obliquityvariations during >10 Ma were chaotic enough. Therefore, ourunderstanding of how the periods of glacial activities have variedin the past is limited (Laskar and Robutel, 1993; Jakosky et al.,1997; Madeleine et al., 2009). The promising traditional landformsthat have developed within the past 10 Ma in Moreux are TCPsand gullies (2.10.4 Ma). Gullies are an outcome of suddenoutburst of fluid due to melting of accumulated ice/snow in alcovesand its rapid flow over a steeper topography incise the top surfacedeep enough to carve channels that ends at the base or flatterzones where it deposits the eroded materials in form of fans(Costard et al., 2002; Christensen, 2003). According to the model-based studies, it was mainly during the mid-day of summer sea-sons that the temperature rose above the melting point of waterand led to the formation of these gullies. This has suggested thatthe conditions favorable for forming gullies were achieved onlyfor some shorter duration during a day (Costard et al., 2002;Martin et al., 1979). Had a gully formed during the past, the melt-ing of accumulated ice/snow could have happened during specificclimatic conditions and the outburst of melted ice could haveoccurred suddenly. If our interpretation is correct, then it impli-cates that the formation of gullies were an outcome of fasterresponse of the surface over which gully has formed respondingto the changes in climate. Similarly, it is commonly understoodthat polygons on Mars are an outcome of freezing and thawingor sublimation of the accumulated ice/snow into the top layer ofthe substrate (Mangold, 2005; Kreslavsky et al., 2008; Levy et al.,2008). To form one closed network of polygons over martian sur-face, a cycle of freezing and thawing process has to complete, dur-ing which, if the strain of the top soil overcome the stress providedby the expanded volume of ice, it cracks and thus the polygonalnetwork forms (Mellon, 1997; Mellon et al., 2008; Levy et al.,2008, 2009). The symmetry of crack formation in the polygonal ter-rain shows that the observed features are an outcome of a longer-term of ice accumulation and ablation on/from the surface withinthis realm. Our interpretation thus implies that formation of TCPsis an outcome of relatively slow response to the changes in climate.We thus hypothesize that gullies and polygons are an outcome oftwo different rates of response (fast and slow) to the changes in cli-mate over a region.

7.3. Older and newer modification sites

Within Moreux, the glacial/periglacial features were observedonly at those sites where accumulation/ablation of ice/snow andflow of ice-debris have taken place. This raises the questionwhether these ice-related features have formed only at some spe-cific sites wherein all the epochs of ice/snow accumulation havetaken place, or there were new sites that received ice/snow onlyduring the recent (minor phase) glacial epoch. If the glacial/peri-glacial features of all the three phases happen to be present at allthe sites of glacial activity within Moreux, then it is difficult to dif-ferentiate the distribution of landforms and answer this question.The best way would be to investigate the plains that are devoidof LDA/LVF-like features (outcome of a major glacial period) andto examine the crater for sites that only bear either the VFFs (out-come of a moderate glacial period) or the polygons/gullies (out-come of a minor glacial period). From our observations, we wereable to demarcate several sites within Moreux fromwhich we havedocumented evidence for isolated occurrence of VFFs and poly-gons/gullies. This indicated that the accumulation of ice/snow con-tinued to vary among different sites within Moreux and newerlandforms gradually developed at newer sites during the majormoderateminor glacial epochs (1 Ga0.4 Ma) (Figs. 7e, 8af,12ai, 15af and 23), aiding in modification of the crater.

7.4. Glacial modification of Moreux

We have presented evidence for recent and episodic modifica-tion of the crater from our observation of geomorphic features overits rim/wall surface and around central peak. In addition, theselandforms imply significant role of ice-rich processes that havealready happened on Mars during different periods of the late

142 R.K. Sinha, S.V.S. Murty / Icarus 245 (2015) 122144Amazonian history. Taken together, to represent the nature ofmodification of craters surface during the past glacial episodeswe envisage four different stages, namely (1) during formation ofLVF/LDA (1 Ga100 Ma), when mobilization of accumulated icepacks had flown debris away from the base of wall or proximalmassifs, forming curvilinear parallel arcuate ridges over the surfacethat terminated as lobe shaped features (Levy et al., 2007; Morganet al., 2009; Baker et al., 2010); (2) during formation of piedmontlobes and lobate flow features around and/or at base of centralpeak (130280 Ma), when glacial ice accumulated within largeralcoves eroded and transported debris downslope as a result ofice sublimation, forming lobate shaped confined flow features thatlastly culminated into a piedmont lobe depending upon the con-finement of the distal margins (Neukum et al., 2004; Milkovichet al., 2006); (3) during formation of viscous flow features (300.1 Ma), when ice accumulated during a less extensive glacial per-iod into alcoves that initiated downslope flow according to thelocal topography, or around or over the topographic obstacles,which lastly terminated with lobe-shaped fronts including pres-ence of linearconcentric ridges on their surface (Milliken et al.,2003; Arfstrom and Hartmann, 2005); and (4) during the recentglacial epoch (2.10.4 Ma) that formed gullies and polygons asa result of minor accumulation and ice/snow melt over smallerportions within/around crater (Head et al., 2003; Levy et al.,2009; Morgan et al., 2010). Since Moreux impact took place onthe dichotomy of Mars, it is expected that the overall shape ofthe crater will not be as consistent as other impact craters formedover topographically flat surfaces. Therefore, the landform evi-dences presented here are only focused to display the modificationof the post-impact surface, i.e. rim/wall surface, floor, and surfacearound central peak, caused by pertinent glacial processes duringthe past 1 Ga0.4 Ma.

8. Summary and conclusions

Our in-depth investigation of a previously undocumented craterprovided convincing evidence for episodic and recent glacial activ-ities in the Protonilus Mensae region and helped us to demonstratethat the different phases of glaciation have played a key role inmodification of the crater surface over the rim/wall and aroundcentral peak. Our key findings are summarized as follows:

1. We found abundant evidence for emplacement of LDA and LVFin different scales within Moreux. Their integrated flow pat-terns are related to the local topography and changes in climateconditions during the major phase of glacial activity (Figs. 8afand 12ai). This is supported by both LDA/LVF types that showtop-down integrated flow patterns from/within alcovesemplaced at top of wall and the observations that they formedduring past 1 Ga100 Ma, corresponding to major phase ofice/snow accumulation.

2. The intriguing lobate flow features at/around the central peakdisplay strong morphological similarities to the features thatare present near Surprise Fjord in the southern part of Axel Hei-berg Island and display a unique example for integrated glacialsystems on Mars.

3. We interpret possibilities for presence of clean glacial ice buriedunder the surface of VFFs interpreted in the region (Fig. 15af).The possible presence of ice is supported by presence of subli-mation tills distributed randomly over the surface of VFFs(Fig. 16). It is expected that ice may be preserved under thosefaces where lag deposits are sufficient to prevent sublimation.

4. We have not found any evidence of channeled flows withinMoreux similar to proglacial valleys or the traditional flowchannels observed elsewhere on Mars. This shows that at theelevation of Moreux in the global Mars, ice has not undergonesufficient melting to induce formation of typical sinuous chan-neled flows. The type of disintegrated ice-related valleysobserved at portions over/around rim/wall of crater (Fig. 18aand b) is believed to have originated under the influence ofthe pressure generated by the overlying ice layer accumulatedduring periods of extensive glaciation.

5. We present evidence for transport of ice-related materials fromadjacent high standing mesas; the flow of LVF materials haveeroded a large portion of Moreux rim and deposited the erodedmaterials onto the floor (Fig. 20a).

6. We suggest that the difference in morphological makeup oflandforms within Moreux has been substantially controlled bythe effect of different rates at which the accumulated ice/snowpacks, at different periods during the past, has responded to theshifts in climate.

These findings from our study lead to the following conclusions:

The surface of Moreux crater over the rim/wall and around cen-tral peak has undergone sequential glacial modification after itsemplacement over the martian dichotomy. The modificationhas been in the form of erosion, transportation, and depositionby both accumulated ice/snow during a large history of Marsand by flow of ice-rich materials in response to ablation and lossof ice/snow pack characterized by climatic changes of a morevarying pattern and shorter duration.

The present character of Moreux indicates periodic phases of icedeposition and glaciation in Protonilus Mensae region. From ourobservation of multitude scale of glacial features within thiscrater, we could suggest that this region is among one of thoseunique sites on Mars where one could analyze all the possibleepisodes of glaciation happened during the past 1 Ga0.4 Ma.

From the trends we observed in the flow characteristics of thelandforms and their typical superposition and stratigraphicrelationships, we conclude that microclimatic shifts played amajor role in reshaping the martian surface and in distributingnumerous glacial/periglacial features that reflect the overallconduct of martian climate and differences in their majormod-erateminor glacial periods.Acknowledgments

We thank Dr. J.S. Kargel and an anonymous reviewer for thecritical reviews, which led to great improvement in the presenta-tion. We thank Vijayan S. for assisting in interpreting crater countinformation. Financial support for this work has been provided byDepartment of Space, Government of India.References

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