Ilaria Di

Antoine Séjourné

François Costard

Marta Ciążela

J Alexis

Palmero Rodriguez

Evidence of mud volcanism due to the rapid compaction of Martian tsunami deposits in southeastern Acidalia Planitia, Mars

Thumbprint terrain was first recognized in Viking Orbiter data and described as sets of alternating continuous parallel ridges and depressions up to several tens of kilometres in length, with high and low albedo respectively. We performed a geomorphological analysis of these features using both Context Camera and High Resolution Imaging Science Experiment images, as well as topographic profiles based on Mars Orbiter Laser Altimeter data, with the aim to provide an origin for thumbprint terrain and constrain the geological evolution of southeastern Acidalia Planitia. The identification of runup lobate deposits, coupled with the putative presence of a Late Hesperian ocean in the northern lowlands, led to speculations that evidence of tsunamis may be present in the geologic record of the area. There are several hypotheses that have been proposed previously to explain the origin of thumbprint terrain and include ice-related, volcanicrelated, liquefaction and mud-volcanism driven processes. However, a tsunami-related origin provides a strong geological framework for the energy required for the associated lobes to flow uphill and leaving peripheral termination ridges as a result of viscosity.

Numerical simulations indicate that -prior to their emplacement -the lobes sustained high velocities, thereby lending further support to the tsunami hypothesis and their origin from the Lomonosov crater impact. Wave interference patterns, formed during the propagation of the tsunamis over and around prominent topography, likely explain the thumbprint terrain spatial arrangement. The thumbprint terrain sedimentary cones are, herein, considered mud volcanoes related to a tsunami that occurred in southeastern Acidalia Planitia.

Introduction

The presence of a Hesperian ocean within the northern plains is one of the most debated issues of the Martian geology [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Head | Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data[END_REF][START_REF] Head | Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF][START_REF] Tanaka | Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data[END_REF][START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. Its presence would imply that northern lowlands gathered a large quantity of water and sediments. Outflow channels, carved by large-scale floods [START_REF] Carr | Formation of martian flood features by release of water from confined aquifers[END_REF], are commonly thought to have served as the primary supply of water which may have filled the northern lowlands in the Late Hesperian [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Baker | Ancient Oceans, Ice Sheets and the Hydrological Cycle on Mars[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. The ocean-hypothesis is supported by several flat surfaces that can be observed spanning thousands of kilometres and marking distinct units in the peripheral northern lowlands. These limits have been interpreted as paleo-shorelines [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF]; for example, the Deuteronilus contact is characterized by very slight topographic variations (-3792 ± 236 m), which are strikingly consistent with the paleo-shoreline hypothesis [START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF][START_REF] Perron | Evidence for an ancient martian ocean in the topography of deformed shorelines[END_REF][START_REF] Citron | Timing of oceans on Mars from shoreline deformation[END_REF]. On the other hand, some limits (i.e., Arabia contact) have topographic amplitudes of up to several kilometres that have initially been used against the ocean hypothesis [START_REF] Head | Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data[END_REF][START_REF] Head | Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data[END_REF]Carr and Head,2003). However, recent studies proposed that these limits represent deformed paleo-shorelines as the result of deformation related to true polar wander occurring before and during the massive Tharsis volcanic rise [START_REF] Citron | Timing of oceans on Mars from shoreline deformation[END_REF][START_REF] Zuber | Oceans on Mars formed early[END_REF] or after the formation of Tharsis region [START_REF] Perron | Evidence for an ancient martian ocean in the topography of deformed shorelines[END_REF]. Several studies have also showed that there could be a large reservoir of water/mud in the deepest portions of the Utopia basin during the Hesperian [START_REF] Ivanov | Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean[END_REF][START_REF] Ivanov | Evidence for large reservoirs of water/mud in Utopia and Acidalia Planitiae on Mars[END_REF]. This may potentially represent the remnant of a larger standing body of water, further supporting the presence of an ocean within the northern plains [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Head | Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data[END_REF][START_REF] Head | Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF][START_REF] Tanaka | Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data[END_REF][START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. Thumbprint terrain (represented hereafter as TT) was previously recognized and described as continuous parallel and curvilinear ridges at regional scale (Fig. 1A white arrow) on the basis of Viking Orbiter data [START_REF] Lockwood | Thumbprint Terrain on the Northern Plains: A Glacial Hypothesis[END_REF]. However, the wealth and increasing resolution of remotely sensed imagery showed it is comprised of both randomly (Fig. 1A black arrow) and highly organized (Fig. 1A white arrow) spatial patterns of individual pitted cones/small mounds that lie above lobate deposits.

Thumbprint terrain overlies millions of square kilometres primarily in the northern plains between 30°N and 50° (e.g., Acidalia Planitia, Utopia Planitia, etc…), although they also occur in a large area near the Martian equator (i.e., Isidis Planitia). Several hypotheses have been proposed for the origin of thumbprint terrain; with the majority of them involving the presence of ice/water. The individual cones were first interpreted as possible pseudo-craters formed by explosions associated with lava emplacement over wet ground [START_REF] Frey | Subkilometer Martian volcanoes: Properties and possible terrestrial analogs[END_REF][START_REF] Carr | Mars -a Water-Rich Planet[END_REF], cinder cones [START_REF] Scott | Map of Mars showing channels and possible paleolake basins[END_REF], pingos, ice-cored ridges [START_REF] Lucchitta | Mars and Earth: Comparison of cold-climate features[END_REF][START_REF] Rossbacher | Ground ice on Mars: Inventory, distribution, and resulting landforms[END_REF], moraines [START_REF] Lucchitta | Mars and Earth: Comparison of cold-climate features[END_REF][START_REF] Scott | Mottled Terrain -a Continuing Martian Enigma[END_REF][START_REF] Kargel | Ancient Glaciation on Mars[END_REF][START_REF] Lockwood | Thumbprint Terrain on the Northern Plains: A Glacial Hypothesis[END_REF], or mounds formed by the disintegration of stagnant ice covers [START_REF] Grizzaffi | Isidis Basin -Site of Ancient Volatile-Rich Debris Layer[END_REF]. According to the most recent hypotheses, they are interpreted as mud volcanism-driven deposits [START_REF] Tanaka | Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data[END_REF][START_REF] Salvatore | On the origin of the Vastitas Borealis Formation in Chryse and Acidalia Planitiae, Mars[END_REF], liquefaction deposits [START_REF] Skinner | Evidence for and implications of liquefaction in the Vastitas Borealis Marginal Unit in southern Utopia Planitia, Mars[END_REF][START_REF] Skinner | Contrasting Flow Events in Chryse and Acidalia Planitiae, Mars, as Determined Through Landform Mapping and Spatial Analyses[END_REF] or related to impact-generated tsunami lobate deposits [START_REF] Rodriguez | Tsunami waves extensively resurfaced the shorelines of an early Martian ocean[END_REF][START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF][START_REF] Costard | The Lomonosov crater impact event: A possible mega-tsunami source on Mars[END_REF].

On Earth, the most common triggers of tsunamis are earthquakes, subaqueous landslides, and volcanic activity. Only on rare occasions meteorite crashes give rise to tsunamis, thus terrestrial impact-induced tsunami deposits are sparse [START_REF] Paris | Tsunamis as geomorphic crises: lessons from the December 26, 2004 tsunami in Lhok Nga, west Banda Aceh (Sumatra, Indonesia)[END_REF][START_REF] Bryant | Tsunami: The Underrated Hazard[END_REF]. Conversely, on Mars, impact-generated tsunamis seem to be a plausible trigger mechanism. The study area (SE Acidalia Planitia) is uniquely positioned in that numerical modelling and geologic investigation tie an asteroid impact (e.g., Lomonosov crater) to the generation of a tsunami wave [START_REF] Iijima | Hydrodynamics of impact-induced tsunami over the Martian ocean[END_REF][START_REF] Rodriguez | Tsunami waves extensively resurfaced the shorelines of an early Martian ocean[END_REF][START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF][START_REF] Costard | The Lomonosov crater impact event: A possible mega-tsunami source on Mars[END_REF] that extended to the areas covered by thumbprint terrain. These numerical predictions, combined with geologic observations, demonstrate the importance of the study area and provides a convincing scenario for thumbprint terrain origin.

Here, we focused on thumbprint terrain (or TT), i.e. alignments of cones or mounds, in the southeastern Acidalia Planitia near the dichotomy (43°-53° N 0°-22° E; Fig. 1B), in an effort to: (i) characterize their geographical distribution; (ii) describe their morphology and relationship with former/underlying topography around the dichotomy and (iii) discuss their origin considering evidences and regional geological context. We will refer to alignments of cones/mounds simply as "thumbprint terrain" or "TT"; while we will refer to both thumbprint terrain and underlying associated lobate deposits as "lobate TT unit".

Although lobate deposits were not the focus of this study, it is useful to have a terminology that indicates both thumbprint terrain and underlying lobes when discussing the overall evolution of the area since target morphologies (TT) are closely related to lobate deposits in SE Acidalia Planitia.

Stratigraphy

The Vastitas Borealis Formation is the most widespread formation in the northern lowlands [START_REF] Greeley | Geologic map of the eastern equatorial region of Mars[END_REF][START_REF] Tanaka | Geologic map of the polar regions of Mars[END_REF]. Many different hypotheses have been proposed to explain its origin, supporting either a sedimentary processes related to outflow channels [START_REF] Kreslavsky | Fate of outflow channel effluents in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water[END_REF] or a volcanic process [START_REF] Catling | Does the Vastitas Borealis Formation contain oceanic or volcanic deposits?[END_REF]. [START_REF] Kreslavsky | Fate of outflow channel effluents in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water[END_REF] asserted that a sedimentary section of the Vastitas Borealis Formation formed as a residue when water from the outflow channels settled, quickly froze, and then sublimated. However, recent studies suggested that portions of Vastitas Borealis Formation were emplaced and/or modified while still saturated with liquid water [START_REF] Mcgill | Origin of Giant Martian Polygons[END_REF][START_REF] Tuckwell | The control of stress history and flaw distribution on the evolution of polygonal fracture networks[END_REF][START_REF] Buczkowski | Formation of double-ring circular grabens due to volumetric compaction over buried impact craters: Implications for thickness and nature of cover material in Utopia Planitia, Mars[END_REF][START_REF] Cooke | Basement controls on the scale of giant polygons in Utopia Planitia, Mars[END_REF][START_REF] Mcgowan | The Utopia/Isidis overlap: Possible conduit for mud volcanism on Mars[END_REF][START_REF] Buczkowski | Giant polygons and circular graben in western Utopia basin, Mars: Exploring possible formation mechanisms[END_REF]. Regional geologic mapping [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]; Fig. 2) separated the Vastitas Borealis Formation into two distinct units: the interior (ABvi) and the marginal unit (ABvm). the ABvi unit is the more extensive of the two units and hosts most of the diagnostic Vastitas Borealis Formation morphological features [START_REF] Salvatore | On the origin of the Vastitas Borealis Formation in Chryse and Acidalia Planitiae, Mars[END_REF]. Data from Mars Orbiter Laser Altimeter (MOLA) derived Digital Elevation Model (DEM) and several 100-m/pixel-resolution Thermal Emission Imaging System images (THEMIS) reveals that the ABvi unit is rougher and has a higher thermal inertia than the ABvm unit (Tanaka et al., 2005, and references therein). The ABvi unit also consists of relatively bumpy, plains-forming material [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF] that covers most of the northern plains including Vastitas Borealis and Utopia, Acidalia, and northern Arcadia Planitiae. The outer parts of the ABvi unit include the lobate TT unit (Fig. 2), as well as random clusters of hills mostly <1 km across [START_REF] Frey | Subkilometer Martian volcanoes: Properties and possible terrestrial analogs[END_REF][START_REF] Grizzaffi | Isidis Basin -Site of Ancient Volatile-Rich Debris Layer[END_REF][START_REF] Scott | Map of Mars showing channels and possible paleolake basins[END_REF]. Approaching the edge of the unit, cones/mounds tend to decrease in quantity, occuring in random and small groups until their complete disappearance [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF][START_REF] Salvatore | On the origin of the Vastitas Borealis Formation in Chryse and Acidalia Planitiae, Mars[END_REF].

Conversely, the ABvm unit outcrops surround the ABvi in Utopia Planitia, along Arabia Terra, in southern Acidalia Planitia, north of Alba Patera, and in western Arcadia Planitia. At lower latitudes (< 25° N), it appears smoother, exhibits a higher albedo and lower thermal inertia than both the ABvi unit and surrounding materials in THEMIS daytime infrared images. This means that the ABvm unit is warmer, which may indicate a relatively fine-grained material compared to adjacent materials [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF].

Parts of the ABvm are buried by Amazonis and Elysium provinces materials. The ABvm unit also includes systems of fretted valleys that are a few kilometres wide and tens of kilometres long [START_REF] Squyres | Martian fretted terrain: Flow of erosional debris[END_REF][START_REF] Carr | The Martian drainage system and the origin of valley networks and fretted channels[END_REF][START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. These features have no clear terrestrial analogues and they have previously been compared to glacial moraines and kame complexes [START_REF] Lucchitta | Mars and Earth: Comparison of cold-climate features[END_REF], glacial tunnel valley and esker features [START_REF] Kargel | Evidence of ancient continental glaciation in the Martian northern plains[END_REF], or soft-sediment deformation structures [START_REF] Tanaka | Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data[END_REF]. The Vastitas Borealis marginal and interior units generally have a poorly defined contact and post-emplacement material evolution. In addition, the southern limit of the collective outer margin of both Vastitas Borealis units is fairly constant in elevation (~ -3900m ± 70m) and close to the mean elevation of the Deuteronilus contact (see section 1), hence it may indicate the presence of an ancient standing body of water [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Head | Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF]. In our study area, the Vastitas Borealis Formation approaches the Noachis Terra unit (Nn) (Fig. 2) and to a lesser extent the Deuteronilus Mensae 1 unit (HBd1; [START_REF] Mangold | Experimental and theoretical deformation of ice-rock mixtures: Implications on rheology and ice content of Martian permafrost[END_REF] (Fig. 2). The Noachis Terra unit is Middle to Late Noachian in age and represents mostly heavily cratered terrain [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. Most of the unit displays layering [START_REF] Malin | Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission[END_REF], in MOC narrow-angle data. Elevation ranges between -2,000 and -5,000 m within the northern plains across Orcus Patera and Acidalia Mensa [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF]. [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF] Lobate TT unit extension is marked by the orange polygons and covers an area bigger than 10 5 km². Red frame indicates the area of quantitative thermal inertia analysis (See section 3). Elliptical domes related to the thumbprint terrain (see Fig. 9-10) are localized outside or along the boundary of the thumbprint area (black triangles are not to scale). The lobate TT unit was mapped crossing both the Vastitas Borealis interior unit (ABvi) and Vastitas Borealis marginal unit (ABvm). Other geologic units: Nn -Noachis Terra Unit; HBd1 -Deuteronilus Mensae unit 1; ABd2 -Deuteronilus Mensae 2 units; HNn -Nepenthes Mensae unit. See [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF], for a more complete description. Courtesy of NASA/USGS.

Data and Methods

Context Camera (CTX; 6m/pixel) [START_REF] Malin | Context camera investigation on board the Mars Reconnaissance Orbiter[END_REF] and High Resolution Imaging Science Experiment (HiRISE; 0.25-0.32m/pixel) [START_REF] Mcewen | Mars reconnaissance orbiter's high resolution imaging science experiment (HiRISE)[END_REF] images were used to investigate thumbprint terrain. CTX images provided a full coverage of the study area to be compared with Mars Orbiter Laser Altimeter (MOLA; [START_REF] Smith | Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars[END_REF] digital elevation model (DEM) which provided the topographic base map with a spatial resolution of 463 m. Detailed topographic profiles were performed from MOLA laser shots (vertical resolution: 50 cm; size of the laser shot on the surface: 128 m) to investigate and to provide a topographic context for TT morphologies and associated lobate deposits (e.g. Fig. 3 and following) thanks to MOLA Precision Experiment Data record (PEDR) facility available at the Photothèque Planétaire d'Orsay, France (http://fototek.geol.upsud.fr/-Mars-Orbiter-Laser-Altimeter-.html). Mars Odyssey (ODY) Thermal Emission Imaging System (THEMIS) daytime and night-time infrared (IR) images (100m/pixel; [START_REF] Christensen | The thermal emission imaging system (THEMIS) for the Mars 2001 Odyssey Mission[END_REF] were also used to investigate the thermophysical properties, including thermal inertia that quantifies the physical properties and average particle sizes of surface textures and morphologies [START_REF] Fergason | High-resolution thermal inertia derived from the Thermal Emission Imaging System (THEMIS): Thermal model and applications[END_REF].

Relief characteristics (slopes and aspects) for the relief correction of albedo and temperature difference (input parameters in Eq. 1) were calculated based on the High Resolution Stereoscopic Camera (HRSC) DEM-s (spatial resolution: 100 m; [START_REF] Neukum | HRSC: the High Resolution Stereo Camera of Mars Express[END_REF][START_REF] Jaumann | The high-resolution stereo camera (HRSC) experiment on Mars Express: Instrument aspects and experiment conduct from interplanetary cruise through the nominal mission[END_REF] in *da4.img format (aeroid directly comparable with MOLA grid) acquired from Mars Orbital Data Explorer (http://ode.rsl.wustl.edu/mars/).

Thermal inertia estimation

We performed a quantitative detailed analysis of thermal inertia on a selected portion of the studied area (Fig. 2). As direct measurement of thermal inertia was not possible to estimate; Differential Apparent Thermal Inertia (DATI) was computed as follows:

𝐷𝐴𝑇𝐼 = 1 -𝐴 ∆𝑇 [Eq. 1]
where A is the albedo and ∆T is the temperature difference. DATI technique (Sabol et 1 al., 2006) is proportional to P ('direct' thermal inertia) and is calculated based on short 2 time (t) intervals (at least one hour time difference) with a high |ΔT/Δt| gradient (in the morning or in the afternoon), preferably during the same period of the year (similar solar longitude).The selected part of SE Acidalia Planitia was chosen on the base of: (i) data availability for DATI calculation (i.e., high quality images with appropriate time interval, in the same period of the year), and (ii) the presence of the key landforms (thumbprint terrain). THEMIS IR images were processed online using the Themis Processing Web Interface (THMPROC; http://thmproc.mars.asu.edu). To calculate the Differential Apparent Thermal Inertia (Eq. 1), high quality THEMIS images were chosen: the minimum and maximum "summing" parameters were set to 1 (full-resolution images), while the minimum and maximum "image rating values" were set to 4 and 7, respectively. These parameters depend on a subjective assessment of the image quality ranging from 1 (unusable) to 7 (very good); this assessment includes consideration of exposure, missing lines, instrument noise, and atmospheric features.

Relief correction for A and ∆T was also performed since this kind of calibration is not included in thermal inertia modelling. Temperature difference (∆T) was additionally calibrated against total incoming energy. Atmospheric correction was also included. In order to avoid large errors by calculating DATI and albedo, the cells with i > 79° were excluded from the calculations.

The uncertainty in DATI calculation arises from errors due to dust opacity, albedo and slope inclination. The errors in daytime THEMIS temperatures may be ±3 K [START_REF] Fergason | High-resolution thermal inertia derived from the Thermal Emission Imaging System (THEMIS): Thermal model and applications[END_REF]. Assuming the temperature amplitude is 20 K and albedo is 0.2, a ±3 K error implies 17% relative error on thermal inertia due to the error of each of two measured temperatures. Dust opacity is 1.6 J m -2 K -1 s -1/2 making up 0.8% of the average DATI, (200 J m -2 K -1 s -1/2 ), and standard deviation (SD) due to seasonal variation of dust opacity in the high-dust season, which is 0.1. We estimate that a dust opacity error of 0.1 generates a relative error of 5.6% on apparent thermal inertia by comparing average DATI values corrected for dust opacities of 0.22 (average), 0.32 (average +1 SD) and 0.12 (average -1 SD). Considering the two errors of 0.8% and 5.6%, the total uncertainty related to dust opacity is 5.7% when applying the rule of error propagation for error addition. The uncertainty of albedo calculation is 8% which generates a 1.5% error on DATI values. The error in computation of slope inclination on HRSC DTM is ~4° [START_REF] Heipke | Evaluating planetary digital terrain models-The HRSC DTM test[END_REF], which can potentially add up to 35% of error on DATI values where the incidence angle is very high (79°). This is calculated by comparing DATIs for 79° to the average DATI for 75° and 83°, provided all other parameters are fixed at typical values. In the most common case where the incidence angle is in the range 0°-50°, the DATI error is within 10%. Taking temperature, dust opacity, slope inclination and albedo into account, the total uncertainty on DATI is estimated to be within 27%. However, it can reach up to 43% when the incidence angle is 79°.

Crater-size frequency distribution

We performed a crater counting analysis using CTX imagery to provide an age estimation for the lobate TT unit deposits. All visible impact craters (>500 m in diameter)

were measured except the aligned secondary clusters and rays within the CTX resolution limit using the ArcGIS add-in CraterTools [START_REF] Kneissl | Map-projection-independent crater size-frequency determination in GIS environments-New software tool for ArcGIS[END_REF][START_REF] Bamberg | Additional tools for surface analysis in ArcGIS[END_REF]. The crater-size frequency distribution (CSFD) was plotted and the crater retention ages were calculated with Craterstats by visually selecting the portion of the crater size-frequency distributions that is parallel to some isochrons between steps of the distribution [START_REF] Neukum | Meteorite bombardment and dating of planetary surfaces. Translation of: Meteoriten bombardement und Datierung planetarer Oberfl€achen[END_REF][START_REF] Hartmann | Cratering chronology and the evolution of Mars[END_REF][START_REF] Platz | Craterbased dating of geological units on Mars: Methods and application for the new global geological map[END_REF].

Results

Thumbprint terrain was usually described as sets of alternating ridges/mounds and depressions, with high and low albedo respectively, up to several tens of kilometres in length (Fig. 1A; [START_REF] Lockwood | Thumbprint Terrain on the Northern Plains: A Glacial Hypothesis[END_REF]. However, we observed no noticeable variations of alternating relief by using MOLA laser shots in our study area (Fig. 3). The low albedo surfaces show a darker rough surface, while the high albedo areas show alignments of poorly expressed mounds (Fig. 4A) that can individually be dome-like (Fig. 4B) or more rarely conical (Fig. 4C) when seen at high resolution. according to Smith et al., 1999;2001. North is oriented 90 degrees right. Courtesy of NASA/ JPL/Univ. of Arizona. Thermal inertia comparisons showed that thumbprint terrain is brighter than the surrounding terrain in day-time THEMIS images, whereas it is darker in night-time ones (Fig. 5). Moreover, the whole lobate TT unit is also generally brighter in day-IR images in comparison to the surrounding plains and plateau units, so we readily defined the lobate TT unit limit realizing: (i) TT is also present in the ABvm unit, although previous literature [START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF] considers that it extends only within the ABvi unit (Fig. 2) and (ii) it covers an extensive surface greater than 10 5 km² in southeastern Acidalia Planitia. Unfortunately, the northern limit of the lobate TT unit in Acidalia Planitia is covered by a unit of lower albedo that has a constant elevation of around -4100m (supplementary material). Therefore, the true extent of the unit remains unknown. In the southern region of the study area, the lobate TT unit covers the plateau and valleys near the dichotomy.

The southern boundary of the unit is marked by several lobate features with peripheral and lateral ridges that sometimes overlap each other in the Deuteronilus valley system [START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF]. The lobes are found inside valleys or on lateral valley plains between -3860 m and -4001 m altitude.

We also observed that lobes are oriented upslope of few degrees (Fig. 6), or on residual hills plains (Fig. 7), reaching a maximum thickness of 10-20 m by using MOLA laser shots [START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF]. Occasionally, the characteristic alignments of cones/mounds tend to distance themselves approaching the edge of the lobate TT unit and do not show the characteristic high albedo small mound chains. Regardless, we included them in the thumbprint terrain unit due to thermal inertia comparisons with surrounding areas, lateral continuity and sparse presence of clusters or individual small mounds. A general southeastward trend has been computed from the analysis of the high albedo mounds (Fig. S1 -supplementary material), even if there are some lobes with random direction because of first-order topographic influence (Fig. S2 supplementary material). Thermal inertia was calculated based on the IR THEMIS data for the part of the thumbprint terrain unit (marked by the black line on Fig. 8A). For this area, DATI values ranges from 171 to 311 indicating fine particles (~40 -500 μm: silt to medium sand) with the average particle size of 125 μm [START_REF] Fergason | High-resolution thermal inertia derived from the Thermal Emission Imaging System (THEMIS): Thermal model and applications[END_REF][START_REF] Wentworth | A scale of grade and class terms for clastic sediments[END_REF]. An average albedo of 0.19 (range 0.15-0.33) calculated for this region based on CTX images further supports the presence of silt and fine sand. (Fig. 8 B). Table 1. Comparative DATI values (J m -2 K -1 s -1/2 ) and particles diameters (µm) of selected materials (after Fergason et al., 2006).

We observed several domes (10-12 kilometres in diameter) near or along the lobate TT unit limit (Fig. 2), making their detection difficult inside thumbprint as the lobate TT unit overlaps them (Fig. 9B). These morphologies are mostly elliptical, have an irregular and lobate edge and show concentric features compared to the central peak (Fig. 9A; Fig. 9B). Smaller features (≈1km in diameter) are observed, but are almost circular and do not show clear concentric lineaments (Fig. 9C). MOLA elevation profiles showed they have a symmetric profile and heights of few tens of meters as shown in Fig. 9A.

Thermal inertia comparisons show that these domes are very bright in day-IR images and darker in the night compared to the surrounding units (Fig. 10). This characteristic is qualitatively similar to the response that thumbprint terrain has to night/day material exposition. In fact, TT is also generally brighter in day-IR images, whereas it is darker during night acquisition (Fig. 5). Since the most recent hypotheses have already provided a regional geological framework for lobate deposits in Acidalia Planitia [START_REF] Rodriguez | Tsunami waves extensively resurfaced the shorelines of an early Martian ocean[END_REF][START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF][START_REF] Costard | The Lomonosov crater impact event: A possible mega-tsunami source on Mars[END_REF], in the following paragraphs we will discuss and consider the characteristics of thumbprint terrain to each of the main geological scenarios (i.e., pingoes, volcanic cones, liquefaction, mud-volcanoes, and tsunami-related deposits) in order to reconcile and insert TT origin in the regional context.

Although the scenario of a periglacial environment has been put aside in favour of more conceivable interpretations in the last years, [START_REF] Rodriguez | Tsunami waves extensively resurfaced the shorelines of an early Martian ocean[END_REF] did not totally dismiss this hypothesis because tsunami deposits could have frozen and formed a layer of permafrost. Moreover, the presence of excess ejecta craters strengthens the occurrence of an icy sub-surface layer that could also be responsible for surficial geological processes as proposed for other geological processes in other areas on Mars [START_REF] Salese | Hydrological and sedimentary analyses of well-preserved paleo fluvial-paleolacustrine systems at Moa Valles, Mars[END_REF]. However, pingoes are domical structures formed by freezing and swelling of groundwater and are, therefore, composed by the same material as their surroundings. Thus, the difference observed between the pitted mounds and the darker adjacent areas in THEMIS images are not consistent with a pingo hypothesis (Fig. 5).

Furthermore, the growth of pingoes is accompanied by radial extension cracks [START_REF] Mackay | The growth of pingos, western Arctic coast, Canada, Can[END_REF]1998), which were not observed in any of our target features and deposits. The high albedo mounds have been also interpreted as moraines, or ice-cored ridges associated with a former glacial environment [START_REF] Lucchitta | Mars and Earth: Comparison of cold-climate features[END_REF][START_REF] Rossbacher | Ground ice on Mars: Inventory, distribution, and resulting landforms[END_REF][START_REF] Farrand | THEMIS Observations of Pitted Cones in Acidalia Planitia and Cydonia Mensae[END_REF], but their exact origin is still under debate. Herein, we find the periglacial origin hypothesis problematic because of thermal inertia comparisons with surrounding deposits (Fig. 5), material viscous behaviour that is not consistent within a periglacial or glacial environment, and the lack of typical glacial features such as polygons, cracks, eskers, drumlins and kettle holes.

Alternatively, over many decades, the associated underlying TT lobate deposits have also been interpreted as lava flows flooded over a broad region forming a volcanic plain.

In this scenario, the high albedo mounds are interpreted in a variety of ways including:

1) rootless cones (pseudocraters) formed by explosions that resulted from a lava flow advancing over a wet substrate [START_REF] Frey | Subkilometer Martian volcanoes: Properties and possible terrestrial analogs[END_REF]; 2) cinder cones formed by explosion and deposition of ashes [START_REF] Wood | Monogenetic volcanoes of the terrestrial planets[END_REF]; or 3) tuff cones resulting from the explosive interaction between rising magma and water/groundwater [START_REF] Wohletz | Hydrovolcanic explosions II. Evolution of basaltic tuff rings and tuff cones[END_REF]. However, thumbprint terrain mounds are brighter than basaltic sands in Acidalia [START_REF] Farrand | Pitted cones and domes on Mars: Observations in Acidalia Planitia and Cydonia Mensae using MOC, THEMIS, and TES data[END_REF] and the DATI values of the TT are much lower than the ones expected for lava flows (Fig. 8; Table 1). In addition, volcanic cones do not form in arrangements that resemble patterns observed within TT. Based on the lack of these conditions, we conclude that a volcanic origin of the thumbprint terrain is unlikely for TT in southeastern Acidalia Planitia.

More recently, thumbprint terrain has also been interpreted as mud volcanoes which formed after the freezing of an ancient standing body and/or rapid sedimentation and diagenesis. The existence of a mud sheet flood has also been proposed for the northern lowlands due to some hills and ground undulations in Isidis Planitia and Mare Australe [START_REF] Farrand | Pitted cones and domes on Mars: Observations in Acidalia Planitia and Cydonia Mensae using MOC, THEMIS, and TES data[END_REF][START_REF] Oehler | Evidence for pervasive mud volcanism in Acidalia Planitia[END_REF][START_REF] Souček | A 3 Ga old polythermal ice sheet in Isidis Planitia, Mars: Dynamics and thermal regime inferred from numerical modeling[END_REF][START_REF] Komatsu | Small edifice features in Chryse Planitia, Mars: assessment of a mud volcano hypothesis[END_REF]. As outflow channels filled northern lowlands [START_REF] Baker | Ancient Oceans, Ice Sheets and the Hydrological Cycle on Mars[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF], the following ice sublimation mostly depended on the accumulation rate of debris on the surface. Sublimation residue would have formed the Vastitas Borealis Formation units. Even a shallow layer of little debris thickness would have decreased sublimation and favoured freezing [START_REF] Farmer | Global seasonal variation of water vapor on Mars and the implications for permafrost[END_REF][START_REF] Carr | D/H on Mars Effects of Floods, Volcanism, Impacts, and Polar Processes[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF]:

both the gradual freezing and the load of the top debris layer make the internal pressure rise. This could have led to mixtures of water, ice, rock/soil and mud expulsion on the surface as proposed in Utopia Planitia in order to explain etched flows and polygonal troughs [START_REF] Ivanov | Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean[END_REF]. This model can also be applied to the thumbprint terrain in Acidalia Planitia since geologic observations and settings are similar. The high albedo mounds could be analogous to terrestrial mud volcanoes with a wide range of different features from meter sized cones to domical structures hundreds of meters in size [START_REF] Kholodov | Mud volcanoes, their distribution, regularities, and genesis: Communication 1. Mud volcanic provinces and morphology of mud volcanoes[END_REF] that are similar in lateral and vertical dimension to the Martian domes and cones of the Acidalia region. However, thermal inertia and albedo values indicate a widespread presence of fine sand and silt (mud?) size grains. The reason could be explained by two fundamental factors that eventually interacted with each other. First, detectable grain-size values might not match mud particle size anymore since the material dried up and got indurated over the time. Ultimately, sandy mud volcanoes have been found on Earth [START_REF] Miyakawa | The origin of muddy sand sediments associated with mud volcanism in the Horonobe area of northern Hokkaido, Japan[END_REF] and, thus, this phenomenon cannot be excluded either. On Earth, tsunamis move landward in a series of wave fronts [START_REF] Lavigne | Reconstruction of tsunami inland propagation on December 26, 2004 in Banda Aceh, Indonesia, through field investigations[END_REF], whose energy and interaction with the shoreline topography results in different inundation distances and distributions of lobate debris. Within the complex topography of flat-floored valleys and plateaus along the Martian dichotomy boundary, the interference of the multiple reflected and refracted waves that are observed in simulations explain the flow distribution itself and the origin of the arcuate and parallel pattern that characterizes the thumbprint terrain. Thumbprint terrain cones are not observed in any terrestrial tsunami, but they are herein considered mud volcanoes that formed as a consequence to an overpressure caused by rapid compaction upon deposition of the transported material during the final stage of a tsunami. A similar geological process was proposed for the emplacement of the Vastitas Borealis Formation in both Chryse and Acidalia Planitia at the regional scale [START_REF] Salvatore | On the origin of the Vastitas Borealis Formation in Chryse and Acidalia Planitiae, Mars[END_REF]. According to this hypothesis, the Vastitas Borealis Formation would be a product of extensive sedimentary modification both during and immediately after outflow channel activity. Mud-extrusion would then result from burial and rapid compaction of previously saturated deposits [START_REF] Salvatore | On the origin of the Vastitas Borealis Formation in Chryse and Acidalia Planitiae, Mars[END_REF]. In our study area, rapid compaction could have expelled a mixed water-mud material, preferentially along the front, and would explain 1) the arcuate or random pattern of thumbprint terrain reflecting the tsunami propagation when influenced by obstacles (Fig.

1A On Earth, geophysical surveys and studies -across the continental margins of the Arctic Oceancontinuously detect suites of hectometre/meter-wide seafloor mounds accompanied with seepage due to the destabilization of gas hydrates (methane) trapped in seafloor and permafrost-associated sediments [START_REF] Serov | Methane release from pingo-like features across the South Kara Sea shelf, an area of thawing offshore permafrost[END_REF][START_REF] Serov | Postglacial response of Arctic Ocean gas hydrates to climatic amelioration[END_REF][START_REF] Andreassen | Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor[END_REF]. Pressure is increased by released methane and triggers blowouts through weakened zones. The Holocene marine transgression affected the Arctic shelves and led to an extensive permafrost thawing; this is the reason why gas hydrate degradation occurs primarily on the circum-Arctic Ocean continental shelves [START_REF] Macdonald | Role of methane clathrates in past and future climates[END_REF][START_REF] Lachenbruch | Permafrost, the active layer, and changing climate[END_REF][START_REF] Maslin | Gas hydrates: past and future geohazard?[END_REF], where subsea permafrost thawing and methane hydrate dissociation have been triggered by warming and inundation since the Late Pleistocene. Seafloor mounds are steep-sided, up to 1100 m wide, generally semi-circular to elliptical in plan view, and have an irregular upper surface incised with straight or curved furrows. Since the mounds are elevated well above the surrounding seafloor, the most plausible formation mechanism is either deposition or uplift. However, the absence of any discernible seismic paleo-seafloor favours the former hypothesis [START_REF] Andreassen | Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor[END_REF]. We find it difficult to attribute thumbprint terrain cones in Acidalia Planitia to these terrestrial shallow-water seamounds considering the scale, mutual geographic distribution, timing of formation and their absence in any terrestrial tsunami deposit since these Martian cones are smaller and more densely coalesced (whether organized or not) than Earth's features.

Therefore, TT mounds/cones are more likely thought as mud-volcanoes related to a catastrophic event (tsunami) rather than a release of pressure that gradually accumulated in the sub-surface due to sediment deposition. However, these terrestrial gas blowouts cannot be ruled out for elliptical domes that have been observed outside or under the thumbprint terrain unit (Fig. 2; Fig. 9) and must be further investigated to fit the Acidalia Planitia thumbprint terrain and tsunami-related deposit. The same qualitative thermal inertia response to daily temperature changes between elliptical domes and thumbprint terrain mounds indicates that: 1) these features might be composed by the same material reflecting the uniformity of lithologies in Acidalia Planitia and 2) both elliptical domes and high albedo mound thumbprint terrain alignments are qualitatively finer grained or more poorly consolidated than surrounding areas. This behaviour fits well with average DATI values and conclusion (see section 4).

Therefore, elliptical domes may be the result of material extrusion (due to gradual freezing and/or the load of top debris) prior to the extensive viscous flowing (tsunami event) that led to the thumbprint terrain unit overlapping them and making dome detection difficult inside the lobate TT unit.

New findings stated that some TT is too young to have experienced the ocean floor environment, and, hence, a tsunami event, according to the current understanding of the cryosphere depth and thermo-chemical structure of Mars [START_REF] De Toffoli | Surface Expressions of Subsurface Sediment Mobilization Rooted into a Gas Hydrate-Rich Cryosphere on Mars[END_REF].

However, some areas of thumbprint terrain may be old enough to have experienced tsunamis. In De Toffoli et al., 2019, 370 Ma may be the age of a possible ice-rich mantle covering the older underlying TT deposit as it was observed in northern Arabia Terra where a similar thumbprint terrain is covered by young ice-rich ejecta from Lyot crater (48°33'42.72"N 18°12'46.78"E). Moreover, when dating surfaces and bedforms, it has been observed that the floor ages of some Martian outflow channels generally equate to younger mesoscale flows (several hundred meters to a few kilometers) instead of those published in more general geologic maps reflecting older and regional scale processes [START_REF] Rodriguez | Did the martian outflow channels mostly form during the Amazonian Period?[END_REF]. If alignments of cones in Acidalia Planitia were as recent as those analysed in Arcadia Planitia [START_REF] De Toffoli | Surface Expressions of Subsurface Sediment Mobilization Rooted into a Gas Hydrate-Rich Cryosphere on Mars[END_REF], their strict occurrence with lobate flow deposits direction and highly organized patterns around obstacles (hills or residual plateaus), matching a very older and distinct tsunami event flow, would be an unusually fortunate coincidence. Consequently, this firmly underlines the importance of investigating thumbprint terrain found in other areas of Mars. High-resolution images may further distinguish multiple TT sets: i) analysing adjacent deposits and the geological context in which they are formed, ii) evaluating origin and/or putative trigger mechanisms discerning any morphological convergence.

The ocean hypothesis remains controversial and explanations have been put forward to account for the presence of the TT in the absence of an ocean. For example, [START_REF] Skinner | Evidence for and implications of liquefaction in the Vastitas Borealis Marginal Unit in southern Utopia Planitia, Mars[END_REF] proposed that the propagation of seismic surface waves through northern plains sedimentary units could have triggered liquefaction and run-up flows along the margins of these deposits. In conclusion, given the morphology, the scale, the thermal inertia analysis, the strict occurrence of thumbprint terrain within lobate deposits and their congruous spatial arrangement with inferred lobes direction, and the significant energy required to surmount little slopes, here we favour a tsunami-related origin for TT in Acidalia Planitia, rather than simply a mud-volcanism deposit.

Conclusions

This paper renewed questions about the presence of a large standing body of water on Mars by analysing thumbprint terrain, lobate morphologies and deposits in southeastern Acidalia Planitia. The most likely hypothesis is a tsunami-related origin, as lobate TT unit characteristics (e.g., viscosity, onslope flows, etc…), geological setting and numeric simulations are comparable to terrestrial tsunami deposits. Lobate deposits inside valleys, peripheral lobes and lateral ridges, as well as the energy required to surmount little slopes, overlap valley walls and reach the plateau, fit well with a viscous flow of fine material from the advance of a tsunami. Here, we interpret that these lobes are the remnant of an impact-induced flow with high energy that produced a large inundation subsequent to one or several tsunamis. In this context, thumbprint terrain would be related to the final stage evolution of the tsunami wave propagation, i.e. mud volcanoes that extruded water-mud mix material along the tsunami wave fronts. A wider coverage of high-resolution data would improve our understanding and reveal new crucial information in the ongoing debate of thumbprint terrain origin.

The presence [START_REF] Parker | Transitional Morphology in West Deuteronilus Mensae, Mars -Implications for Modification of the Lowland Upland Boundary[END_REF][START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF][START_REF] Head | Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data[END_REF][START_REF] Head | Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data[END_REF][START_REF] Clifford | The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains[END_REF][START_REF] Carr | Oceans on Mars: An assessment of the observational evidence and possible fate[END_REF][START_REF] Tanaka | Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data[END_REF][START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF], and eventual freezing [START_REF] Ivanov | Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean[END_REF], of a former northern body of water, or a mud-ocean as [START_REF] Jöns | Large fossil mud lakes or giant mud sheet floods in Syrtis Major (Isidis Planitia) and Mare Australe[END_REF] proposed, provides the geological context for thumbprint terrain as mud volcanoes related to a tsunami event. In addition, crater counting showed that lobate TT unit is Early Amazonian; 2.8 ± 0.2 Gyr according to Hartmann 2004-iteration (Fig. S4 supplementary files). This crater counting analysis is concordant to a crater-retention age of 2.9 Gyr, proposed by [START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF] for the same area, and to other previous literature [START_REF] Hiesinger | Thumbprint Terrain in Isidis Planitia, Mars: Geology, Ages, Morphology, and Morphometry[END_REF]) which corresponds to an Early Amazonian/Late Hesperian ocean, in agreement with [START_REF] Parker | Coastal Geomorphology of the Martian Northern Plains[END_REF]. The Late Hesperian is also the timing of peak outflow channel activity, and thus is consistent with the presence of a transient northern ocean ~3 Ga.

Giving morphologies and scales, fully thermal inertia and albedo values compliance, multiple impact craters possibility fitting numerical simulations, the occurrence of TT with lobes, their congruous alignments with inferred lobes direction and in favour of a general geological context, we herein mainly support the tsunami-driven mud-volcanoes hypothesis rather than others mentioned above.

Figure 1 .

 1 Figure 1. Thumbprint terrain in Acidalia Planitia. A) Thumbprint terrain at low resolution with a random arrangement (black arrow) on the left and an arcuate and parallel linear disposition (white arrow). B) Study area is marked by the black rectangle on the topographic map based on colorized Mars OrbiterLaser Altimeter data. Courtesy of NASA/JPL/Univ. of Arizona.

Figure 2 .

 2 Figure 2. Background geological map is'US Geological Survey Sci. Inv, Map 2888[START_REF] Tanaka | Geologic map of the Northern Plains of Mars[END_REF] Lobate TT unit extension is marked by the orange polygons and covers an area bigger than 10 5 km². Red frame indicates the area of quantitative thermal inertia analysis (See section 3). Elliptical domes related to the thumbprint terrain (see Fig.9-10) are localized outside or along the boundary of the thumbprint area (black triangles are not to scale). The lobate TT unit was mapped crossing both the Vastitas Borealis interior unit (ABvi) and Vastitas Borealis marginal unit (ABvm). Other geologic units: Nn -Noachis Terra Unit; HBd1 -Deuteronilus Mensae unit 1; ABd2 -Deuteronilus Mensae 2 units; HNn -

Figure 3 .

 3 Figure 3. Topography of the thumbprint terrain. A topographic profile crossing the high and low albedo area was performed by using MOLA laser shots. No clear topographic alternation is observed between the two areas. The black points represent the approximate size of the laser shot on the surface (128m)

Figure 4 .

 4 Figure 4. Morphology of thumbprint terrain at high resolution. A) High albedo areas include mounds and pits while low albedo areas are composed of a rough surface (HiRISE image: ESP_011949_2255). The high albedo areas of the thumbprint terrain include mounds that may be B) dome-like (HiRISE image: PSP_001928_2265) or more C) cone-like shaped mounds (CTX image: P22_009747_2239). The former type is usually bigger in diameter than the latter, but no clear correlation was found. Courtesy of JPL/Univ. of Arizona.

Figure 5 .

 5 Figure 5. THEMIS daytime and night-time infrared images of thumbprint terrain. The low albedo areas are darker in night-time images (A) and brighter in daytime ones (B). Night-time image resolution is lower than the daytime resolution.

Figure 6 .

 6 Figure 6. Longitudinal profile (A-A') and cross-section (B-B') of a southern limit lobate TT unit deposit from MOLA DEM. ΔL=12000m; ΔH=138m. Lobate TT unit limits are marked by red dots on the image and on profiles as well. Relative slope value is ≈ 0.70°. CTX images: P18_008112_2251; P18_007901_2250; P18_008046_2253; P21_009338_2253.

Figure 7 .

 7 Figure 7. Thumbprint terrain deposits can move upslope reaching plateau residual hills. Thumbprint terrain limit that is marked by red dots on the image and on A-A' MOLA shots profile as well (CTX image: B02_010261_2248). North is oriented 90 degrees left.

Figure 8 .

 8 Figure 8. Thermal inertia analysis. A) DATI (J m -2 K -1 s -1/2 ) values for the selected part of the study area shown in Fig.2. B) albedo values. Lobate thumbprint terrain unit extension is marked by the black line. The location of Fig. 8 is also shown in Fig.2. Top-left corner coordinates: 15°39'58.366"E; 49°41'20.171"N.

Figure 9 .

 9 Figure 9. Large domes underlying thumbprint terrain unit. A) MOLA laser shot cross-section cutting a dome that is found outside thumbprint terrain unit. Central peak and some relating concentric features are visible. The edge is elliptical and quite regular. The boundary is marked by red dots. Dome height is ≈ 40m (CTX image: B17_016195_2250). North is oriented 90 degrees right. B) Dome overlapped by thumbprint terrain. Black dashed line marks thumbprint terrain unit limit. Central peak, some concentric features and an irregular and lobate edge are observed. (CTX image:

  Furthermore, we need to take into account the coexistence of TT with lobate underlying deposits which points to flows with a certain viscosity: the lobate deposits with peripheral ridges clearly indicate that viscous material flowed inside southern valleys(Fig. 6; Fig. 11; supplementary material) and that the plateau and hills were partially flooded (Fig.7; Fig.S1-supplementary files). Additionally, parallel and arcuate alignments of mounds/cones (thumbprint terrain) observed together around obstacles as knobs, residual hills, and plateaus (Fig.1A, white arrow, Fig.S1-supplementary files), perfectly follow the inferred underlying lobate deposits flow direction (Fig.11, Fig.S1and Fig.S2-supplementary material). In the occurrence of an impact-generated tsunami: obstacles might have first influenced flow direction and speed (tsunami wave fronts), forming thumbprint terrain in parallel and curvilinear patterns. Nevertheless, an impact-generated tsunami provides an explanation to the main concern about the energy required to flow up slopes and reach topographic heights. In a previous work, three craters (30-50 km in diameter) were proposed (Fig.S3-supplementary files) as the sources of the tsunami events, based on validated terrestrial models scaled to Mars (wave height, propagation, run up elevation, and distance)[START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF]. The numerical tsunami simulations presented in[START_REF] Costard | Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean[END_REF] link the TT alignments to interference patterns produced from the interaction between the tsunami fronts and the coastal topography. By binding the numeric simulation results to the morphological observations, we assert that a tsunami event contributed to the formation of TT mudvolcanoes.

  -white arrow) or not (Fig. 1A -black arrow), respectively and 2) the gradual disappearance of TT cones toward the unit boundary as compaction, and hence overpressure, should have decreased as the tsunami wave propagation progressively lost energy and material while moving 'landward'.

Figure 11 .

 11 Figure 11. Lobes flow direction inferred from mounds alignments as marked by dashed black arrows. Contour lines are 50 meters spaced. They show that flows clearly go upslope. g18_025425_2271; b18_016498_2264. Inset: Thumbprint terrain flow exceeding valley scarp (dashed red line) for several kilometers. Unit limit is marked by the red dashed line. The lobe has no peripheral ridges and its front is lobate (HiRISE ESP_016498_2265).

Acknowledgements

This research was partially conducted and supported by the Programme National de Planétologie (PNP) of Institut National des Sciences de l'Univers (CNRS-INSU), the Centre National d'Etudes Spatiales (CNES). The EXOMHYDR project within the TEAM

P21_009391_2238). North is oriented 90 degrees right. C) Small circular dome that does not show a clear/regular limit or concentric features related to the centre (CTX image: G23_027087_2234).

Discussion

programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund (contract TEAM/2016-3/20). Our gratitude also goes to Dr. Jakub Ciazela for contribution in the ATI method and estimation of ATI errors. A special thanks goes to Professor Lucia Marinangeli who supported us actively and made it possible to conclude the study.