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The Sirente crater field (Central Italy) consists of a main, ≈130 m wide, droplet-shaped in plan view depression with a prominently elevated rim, and 30 smaller depressions in its close vicinity. It was discovered in 2002 and proposed to be of meteorite impact origin based on its geological and geomorphological similarities to known crater fields. It is developed in non-lithified lake sediments (i.e. carbonate mud). Given the age of formation in the 3rd to 5th centuries A.D., the inferred catastrophic origin was, in the media, soon related to the celestial sign (“Chi Rho”) said to have been seen by Emperor Constantine in 312 A.D. and suggested to have changed the course of both Roman and Christian history. However, the meteoritic origin is not yet confirmed and has been contested. This work presents new geophysical data on the subsurface structure of the main crater, which provides further clues around the controversy of its origin. Two roughly transversal seismic reflection profiles across the main crater reveal a deep (53 m on average), rootless, bowl-shaped structure with a poorly developed, deep-seated central mound, as well as different seismic facies representing a crater infill of disturbed material resembling the breccia lens in craters formed in rock. This survey also allowed the recognition of possible compaction-fissures and upturned strata below the rim, similar to what is known from explosion craters in porous, unconsolidated targets. Some of these structures had already been noted in published resistivity surveys (ERT). The structural features noted in this geophysical survey are consistent with the impact hypothesis and do not support other proposed mechanisms of formation such as karst or mud volcano.

Aeolis Dorsa is a topographic depression, ∼800 km east of Gale Crater, located along the Mars’ dichotomy boundary. This area hosts a set of fluvial sedimentary rocks displaying an exceptional record of depositional environments and fluvial channels patterns that suggest the presence of a large amount of surface and/or subsurface water. We interpreted the plain as an ancient waterlogged environment, a sedimentary basin passing into distal depositional environments. Regional mapping of the area revealed the presence of a large-scale fluvial system that points to a long-term and extensive hydrological cycle. A significant wet period with changing environmental conditions in Hesperian/Amazonian occurred in the study area diverging from the present-day climate. Our map (Main Map) contributes to the understanding of past climatic conditions on Mars. Moreover, it provides an interesting perspective for future missions looking for evidence of present-day and/or past extraterrestrial organisms as the life as we know it needs liquid water.

International audience; Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the polar regions, measured the depth of several lakes and seas, detected temporal changes on its surface, and provided key evidence that Titan contains an interior ocean. As a result of the Cassini mission, Titan has gone from an uncharted world to one that exhibits a variety of Earth-like geologic processes and surface-atmosphere interactions. Titan has also joined the ranks of “ocean worlds” along with Enceladus and Europa, which are prime targets for astrobiological research.

The Dallol volcano and its associated hydrothermal field are located in a remote area of the northern Danakil Depression in Ethiopia, a region only recently appraised after decades of inaccessibility due to severe political instability and the absence of infrastructure. The region is notable for hosting environments at the very edge of natural physical-chemical extremities. It is surrounded by a wide, hyperarid salt plain and is one of the hottest (average annual temperature Dallol : 36-38°C) and most acidic natural systems (pH Dallol ≈0) on Earth. Spectacular geomorphologies and mineral deposits produced by supersaturated hydrothermal waters and brines are the result of complex interactions between active and inactive hydrothermal alteration of the bedrock, sulfuric hot springs and pools, fumaroles and geysers, and recrystallization processes driven by hydrothermal waters, degassing, and rapid evaporation. The study of planetary field analog environments plays a crucial role in characterizing the physical and chemical boundaries within which life can exist on Earth and other planets. It is essential for the definition and assessment of the conditions of habitability on other planets, including the possibility for biosignature preservation and in situ testing of technologies for life detection. The Dallol area represents an excellent Mars analog environment given that the active volcanic environment, the associated diffuse hydrothermalism and hydrothermal alteration, and the vast acidic sulfate deposits are reminiscent of past hydrothermal activity on Mars. The work presented in this paper is an overview of the Dallol volcanic area and its hydrothermal field that integrates previous literature with observations and results obtained from field surveys and monitoring coupled with sample characterization. In so doing, we highlight its exceptional potential as a planetary field analog as well as a site for future astrobiological and exploration programs, This is a contribution to the Europlanet 2020 Research Infrastructure programme funded under the European Commission's Horizon 2020 programme (No. 654208

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars., European Union’s Horizon 2020 research and innovation program under Grant Agreement No 654208

Understanding the origin (volcanic or sedimentary) and timing of intercrater plains is crucial for deciphering the geological evolution of Mars. We have produced a detailed geological map of the intercrater plains north of the Hellas basin, based on images from the Mars Express High-Resolution Stereo Camera, the Mars Reconnaissance High-Resolution Imaging Science Experiment, and Context. Erosional windows and fresh impact craters provide a way of studying the lithology of intercrater plain units. They are composed predominantly of light-toned sedimentary rocks with subhorizontal bedding over a broad extent (greater than tens of kilometers), showing cross-bedding stratifications locally. The broad extent, geometry, and flat topography of these sediments favor a formation by aqueous processes (alluvial and lacustrine) rather than airfall (eolian and volcaniclastic). The Late Noachian (~3.7 Ga) sedimentary plains are locally covered by dark-toned, rough-textured lava flows of Late Hesperian age (~3.3 Ga). Fe/Mg phyllosilicates were detected within sedimentary rocks, whereas volcanic rocks contain pyroxene and lack signatures of alteration, in agreement with interpretations made from texture and morphology. In erosional windows, the superimposition of sedimentary rocks by younger volcanic flows enables the estimation of an erosion rate of ~1000 nm yr−1 during the Hesperian period (3.3–3.7 Ga). Thus, our study shows that an intense sedimentary cycle occurred on the northern rim of the Hellas basin before and during the Late Noachian, leading to the formation of widespread sedimentary plains, which were then eroded, in agreement with a gradual change in the climatic conditions in this period, and later covered by volcanic flows.

Imdr Regio is a volcano dominated young topographic rise of Venus whose most prominent volcanic structure, Idunn Mons, shows indications of being recently active. Despite its scientific relevance, this region has been poorly studied to date. Idunn Mons is spatially related to a rift system, Olapa Chasma, which dominates the topographic rise. The rift fractures around Idunn Mons form an “hourglass” pattern indicating a close tectonic interaction between the volcano and Olapa Chasma. The principal aim of this work is to understand whether Olapa Chasma has been tectonically active in the recent geologic past. For this purpose, we analyzed Sandel crater (45.7°S/211.7°E), an impact structure 17.9 km in diameter situated NW of Idunn Mons, and we used it as a local stratigraphic marker. Observing the variations in the radar brightness and crosscutting relationships, we produced a local geologic map of impact deposits, volcanic materials and tectonic structures surrounding the crater. Then, we used the map to reconstruct the local stratigraphy and relative ages of the materials for deciphering the temporal relations between the crater and volcano-tectonic activity. Following the existing degradation models for Venusian craters we could also estimate a time range for the formation of Sandel crater. The results show that its formation convincingly occurred during the period between 0.5 T and 0.15 T, where T is the average age of the surface of Venus. We present here a line of evidence that, at least in its last stage, the tectonic activity characterizing Olapa Chasma and Idunn Mons postdate the formation of Sandel crater. Building on the findings from previous studies, we hypothesize that not only volcanism but also the tectonic processes behind the formation of Idunn Mons and Olapa Chasma are geologically recent. For this reason, we refer to Olapa Chasma and Idunn Mons as a recently active volcano-tectonic system of Venus, which deserves to be a potential target site for future missions to Venus, including investigations of surface volcanism and seismicity.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Globorotalia bouregregensis, n. sp., is described and documented from the latest Miocene-early Pliocene sequence of the Rifian Seaway, northwest Morocco. By its short stratigraphic distribution, persistence and distinctive morphologic features, the new taxon is well differentiated within the scituline assemblage.

Finally, we would like to recognize the help and support of ESA, Roscosmos, the European states and agencies participating in the ExoMars program, and NASA. We really are doing this together for the benefit of all., The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information., European Space Agency, Roscosmos, ExoMars program, National Aeronautics & Space Administration (NASA)

Martian caves are regarded as one of the most interesting locations in which to search for life on the planet. Data obtained during the MARS2013 expedition at Hamar Laghdad Ridge in the Tafilalt region of Morocco indicate that even small cavities can display thermal behavior that is characteristic for caves. For example, temperature in a cavity equaled 14°C±0.1°C before sunrise, which was higher than the temperature of the ambient air (10°C±0.1°C) and proximate rocks (9°C±0.1°C) at the same time. Within 30 min after sunrise, when the temperature of surrounding rocks corresponded to 15°C, this thermal relationship reversed. Measurements were conducted under simulated spaceflight conditions, including near-real-time interpretation of data that were acquired in a complex flight planning environment. We conclude that using ground-based thermal contrast measurements, in 7-14 μm band before and after sunset, is an effective method for Mars astronauts to identify caves, possibly superior to usage of space-based or ground-penetrating data.

Sand dune migration is documented with a readily-available tool (Google Earth) near Chott El Gharsa, just north-west of Tozeur, Tunisia. As fiducial markers we employ a set of buildings used to portray the fictional city Mos Espa. This set of ~ 20 buildings over roughly a hectare was constructed in 1997 for the movie Star Wars Episode 1 — The Phantom Menace. The site now lies between the arms of a large “pudgy” barchan dune, which has been documented via satellite imaging in 2002, 2004, 2008 and 2009 to have moved from ~ 140 m away to only ~ 10 m away. Visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position: a smaller set nearby was substantially damaged by being overrun by dunes circa 2004. The migration rate of ~ 15 m/yr decreases over the observation period, possibly as a result of increased local rainfall, and is consistent with barchan migration rates observed at other locations worldwide. The migration rate of this and two other barchans suggests sand transport of ~ 50 m3/m/yr, somewhat higher than would be suggested by traditional wind rose calculations: we explore possible reasons for this discrepancy. Because of the link to popular science fiction, the site may be of pedagogical interest in teaching remote sensing and geomorphic change. We also note that nearby playa surfaces and agricultural areas have a time-variable appearance. The site's popularity as a destination for Star Wars enthusiasts results in many photographs being posted on the internet, providing a rich set of in-situ imagery for continued monitoring in the absence of dedicated field visits.

International audience; Gullies on terrestrial sand dunes are rare, and their presence on Mars, as well as their mechanical properties, and the quantity of fluid required for their formations currently remain poorly understood. This study focuses on gully morphologies on the Russell megadune (54.5°S; 12.7°E) using High Resolution Imaging Science Experiment (HiRISE) images and Digital Terrain Models (DTM). Based on the scenario of ground ice melting in a periglacial environment, we propose to test the hypothesis that Martian gullies on dunes are debris flows. This implies a flow with a significant proportion of liquid water (>10% in volume). We used an original method to study Martian gullies based on empirical equations from terrestrial debris flows in order to calculate the physical properties of Martians flows. We observe a decrease in viscosity induced by the relative increase of fluid concentration (from 28% to 39%) during the flow advance. The total estimated volume of eroded and deposited material range from ~14850 m3 to ~18890 m3. The volume of liquid water required to generate one gully ranges from 4450 m3 to 6900 m3. The calculated results for Martian gullies are consistent with terrestrial studies on debris flows. Based on a morphological description and on the estimated physical parameters, we propose a model for gully formation on Martian dunes. The melt water from near-surface ground ice is incorporated in the debris flow and water concentration increases during its propagation. The increase of water concentration in the debris flow can be explained by a progressive increase of water/ice content in the permafrost downstream. Consequently, the lack of a final deposit at the front of the gullies tends to demonstrate that the flow became relatively highly concentrated in liquid downstream and all the water could have been lost in the final stage of the flow. This process could explain the lack of terminal lobes at the front of the gullies. We conclude that a process of formation similar to terrestrial debris flows is plausible. The large amount of liquid water involved requires formation of Martian gullies on dunes during a warmer climatic episode.

In this work we analyze a dark erg on Mars that could be considered a mega-dune (draa) where secondary dunes of different morphology are superposed over a main crescent-shaped bedform (primary dune). The presence of a complex, multi-directional wind regime is indicated as one of the main causes for the accumulation of a tall draa, presenting an analogy to the Great Sand Dunes in Colorado. In both cases, main regional winds from the SW blow in opposition to winds from the NE which are enhanced by the topography. Such a complex wind regime leads to the development of star and reversing dunes and is accurately predicted by atmospheric models on a regional and local scale. Signs of activity in the form of grainflow scars are also noted over the slip faces of many dunes, suggesting that easterly winds are actively shaping the study draa in the present-day climatic setting. The presence of this draa on Mars suggests a complex interaction between regional and local topographically controlled flows and a consistent availability of sand. The future study of an analogue terrestrial site such as the Great Sand Dunes could be fundamental for understanding the evolution of similar Martian dune fields. Copyright © 2012 John Wiley & Sons, Ltd.

International audience; Iron-framboids in the context of a Middle Devonian, hydrocarbon-seep conical mound (Anti-Atlas, Morocco) have been thoroughly investigated through a combination of techniques, including optical and high resolution scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, Raman microscopy and time-of-flight secondary ion mass spectroscopy. Framboids occur embedded in laminated carbonates of the mound and are precipitated along the veins that crosscut it and served as the conduits for (channeled) reduced hydrocarbon-rich fluids. The morphology, structure, and composition of the framboids contribute to the reconstruction of the complex interplay between the advected fluids and the associated biological and/or abiological processes. A comparison of our dataset with that from modern framboids formed under similar conditions indicates that the Fe-rich framboids represent replaced primary pyrite framboids produced as a consequence of bacterial sulfate reduction and the anaerobic oxidation of methane.

We report the detection of mound-like landforms interpreted as mud volcanoes within Firsoff crater, in the Arabia Terra region of Mars. The mounds stratigraphically overlie layered deposits within the crater, which consist of high albedo well-bedded deposits disrupted in meter-sized polygons. Hundreds of mounds are observed on the crater floor, as isolated or composite subcircular cones 100–500 m in diameter and tens of meters high. More than one third of the mounds (35%) have subcircular depressions 5–39 m in diameter at their apices that we interpret as vents. The mounds consist of meter-sized boulders of high albedo, embedded in an apparently finer-grained unit; we interpret these deposits as mud volcanic breccia, containing boulders of reworked light-toned layered deposits carried upward from deeper portions of the succession. The mounds are mainly located near the rim-bordering faults and in places aligned with fractures, suggesting subsurface pathways for fluid migration. The mounds are interpreted as fossil mud volcanoes, recording the upward migration of overpressured fluids through the crater infill from deeper crustal sources, localized by impact-related faults. The geological conditions and processes that might have controlled sedimentary expulsion on Mars are discussed. Mud volcanism has most of its controls in the subsurface. As a consequence, subsurface fluid flow processes could be expected in other craters within Arabia Terra and are less likely in higher, adjacent highland terrains.

We discuss in this paper possible roles of methane and carbon dioxide in geological processes on Mars. These volatiles in the martian crust may migrate upward from their sources either directly or via various traps (structural, sedimentary, ground ice, gas hydrates). They are then likely emitted to the atmosphere by seepage or through diverse vent structures. Though gas hydrates have never been directly detected on Mars, theoretical studies favor their presence in the crust and polar caps; they could have played an important role as significant gas reservoirs in the subsurface. The martian gas hydrates would possibly be a binary system of methane and carbon dioxide occupying clathrate cavities. Landforms such as mud volcanoes with well-known linkage to gas venting are extensively distributed on Earth, and methane is the primary gas involved. Thus, identification of these landforms on Mars could suggest that methane and possibly carbon dioxide have contributed to geological processes of the planet. For example, we present a newly identified field in Chryse Planitia where features closely resembling terrestrial mud volcanoes occur widely, though with no observable activity. We also present results of a preliminary search for possible recent or present-day, methane-emission zones in the regions over which enrichments of atmospheric methane have been reported.

An aeolian system located in Aonia Terra (eastern Thaumasia region) consists of six dark dune fields. The dune pattern suggests an organized extended sand transport system, which is characterized by the presence of long sand corridors. The latter connects the different ergs with potential sources. The sand stored in the ergs is provided by layered materials exposed in pits and crater walls and by the ergs themselves. Most of the sand converges from the marginal dune fields into the central erg C. The latter develops in an area of convergence of at least three different winds: from the southwest, the northeast and the northwest. The northwesterly flows seem to postdate the other winds as suggested by the development of a complex dune pattern in the western portion of the erg C, representing a successive episode of aeolian construction. Collectively such complex dune patterns show how dune fields could record major changes in the wind regimes of Mars.

A variety of sedimentary deposits is observed in Xanthe Terra, Mars, including Gilbert-type deltas, fan deltas dominated by resedimentation processes, and alluvial fans. Sediments were provided through deeply incised valleys, which were probably incised by both runoff and groundwater sapping. Mass balances based on High-Resolution Stereo Camera (HRSC) digital terrain models show that up to ∼30% of the material that was eroded in the valleys is present as deltas or alluvial fan deposits. Stratigraphic relationships and crater counts indicate an age of ∼4.0 to ∼3.8 Ga for the fluvial activity. Hydrologic modeling indicates that the deposits were probably formed in geologically very short time scales. Our results point to episodes of a warmer and wetter climate on early Mars, followed by a long period of significantly reduced erosion rates.

Cassini radar images show a variety of fluvial channels on Titan's surface, often several hundreds of kilometers in length. Some (predominantly at low- and mid-latitude) are radar-bright and braided, resembling desert washes where fines have been removed by energetic surface liquid flow, presumably from methane rainstorms. Others (predominantly at high latitudes) are radar-dark and meandering and drain into or connect polar lakes, suggesting slower-moving flow depositing fine-grained sediments. A third type, seen predominantly at mid- and high latitudes, have radar brightness patterns indicating topographic incision, with valley widths of up to 3 km across and depth of several hundred meters. These observations show that fluvial activity occurs at least occasionally at all latitudes, not only at the Huygens landing site, and can produce channels much larger in scale than those observed there. The areas in which channels are prominent so far amount to about 1% of Titan's surface, of which only a fraction is actually occupied by channels. The corresponding global sediment volume inferred is not enough to account for the extensive sand seas. Channels observed so far have a consistent large-scale flow pattern, tending to flow polewards and eastwards.

The paradigm of an ancient warm, wet, and dynamically active Mars, which transitioned into a cold, dry, and internally dead planet, has persisted up until recently despite published Viking-based geologic maps that indicate geologic and hydrologic activity extending into the Late Amazonian epoch. This paradigm is shifting to a water-enriched planet, which may still exhibit internal activity, based on a collection of geologic, hydrologic, topographic, chemical, and elemental evidences obtained by the Viking, Mars Global Surveyor (MGS), Mars Odyssey (MO), Mars Exploration Rovers (MER), and Mars Express (MEx) missions. The evidence includes: (1) stratigraphically young rock materials such as pristine lava flows with few, if any, superposed impact craters; (2) tectonic features that cut stratigraphically young materials; (3) features with possible aqueous origin such as structurally controlled channels that dissect stratigraphically young materials and anastomosing-patterned slope streaks on hillslopes; (4) spatially varying elemental abundances for such elements as hydrogen (H) and chlorine (Cl) recorded in rock materials up to 0.33 m depth; and (5) regions of elevated atmospheric methane. This evidence is pronounced in parts of Tharsis, Elysium, and the region that straddles the two volcanic provinces, collectively referred to here as the Tharsis/Elysium corridor. Based in part on field investigations of Solfatara Crater, Italy, recommended as a suitable terrestrial analog, the Tharsis/Elysium corridor should be considered a prime target for Mars Reconnaissance Orbiter (MRO) investigations and future science-driven exploration to investigate whether Mars is internally and hydrologically active at the present time, and whether the persistence of this activity has resulted in biologic activity.

Veins cutting across the Devonian conical mounds of the Hamar Laghdad Ridge (eastern Anti-Atlas, Morocco) were the carriers of geofluids. Although not completely determined, the composition of these fluids seems related to hydrothermal and seepage fluxes that were the primary contributors to the establishment of sub-seafloor (cryptic) environments linking deeper fluid sources to the seafloor. The optical and scanning electron microscope investigation of the laminated carbonate infill of these veins has revealed that they consist of stromatolite- and oncolite-like fabrics. In the Early and Middle Devonian mounds, the laminated carbonates contain morphologies that are attributable to microbially mediated processes that in turn suggest a direct biological contribution to the deposition of the veins infill. Microbial evidence include rod-shaped and cocci clusters embedded in amorphous membranes, iron-rich filaments organized as mat-like and biodictyon filamentous aggregates, or isolated filaments, microbial clotted textures and peloids. Moreover, the oncoids from the veins of the Middle Devonian (Hollard) mound have been interpreted as the mineral replacement of crypto-microorganisms as Frutexites . Other microbial evidence are biominerals and include carbonate with spheroids and pyrite framboids, in which typifying hydrocarbon seep environments. The Hollard Mound, which is the only one with a well-documented origin by hydrocarbon seepage, shares a number of geomicrobiological evidence with other Early Devonian mounds. These evidence, which are supplemented by δ 13 C-depleted data, suggest that the infill of the veins system in the Hamar Laghdad mounds would be the product of chemotrophic/chemosynthetic microbial communities that are adapted to crypto-habitats sustained by hydrocarbon (and other components) fluid fluxes.

The basaltic Azas Plateau volcanic field is located in the Tuva Republic of the Russian Federation. The area was glaciated multiple times, and the field is characterized by the formation of subglacial volcanoes called tuyas, but subaerial volcanoes and lava fields also exist. A combined study of remote sensing and field observations in the vicinity of the tuyas in the southeastern Azas Plateau volcanic field identified landforms that are best explained by the jokulhlaup hypothesis. The landforms include elongated hills, paleochannels, and butte and basin topography. These landforms are hypothesized to have formed by both erosion and deposition caused by high-energy water streams. The triggering for the hypothesized jokulhlaups was either melting of ice by subglacial volcanism and/or destabilization of ice-dammed/subglacial reservoirs. The age estimation of the flood events is difficult, but they probably occurred during the ice ages of the Quaternary, as late as in the Middle-Late Pleistocene.

International audience; The Cassini Titan Radar Mapper obtained Synthetic Aperture Radar images of Titan's surface during four fly-bys during the mission's first year. These images show that Titan's surface is very complex geologically, showing evidence of major planetary geologic processes, including cryovolcanism. This paper discusses the variety of cryovolcanic features identified from SAR images, their possible origin, and their geologic context. The features which we identify as cryovolcanic in origin include a large (180 km diameter) volcanic construct (dome or shield), several extensive flows, and three calderas which appear to be the source of flows. The composition of the cryomagma on Titan is still unknown, but constraints on rheological properties can be estimated using flow thickness. Rheological properties of one flow were estimated and appear inconsistent with ammonia-water slurries, and possibly more consistent with ammonia-water-methanol slurries. The extent of cryovolcanism on Titan is still not known, as only a small fraction of the surface has been imaged at sufficient resolution. Energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of Titan.

Gully morphology (often summarized as comprising an alcove, channel and debris apron) is one of the key elements used to support the argument for liquid water in the recent past on Mars. Nevertheless, the processes that create different gully morphologies, on both Mars and Earth, are not fully understood. One of the puzzling morphologic attributes of Martian dune gullies is their apparent lack of an apron, or terminal deposit, which has caused debate about their formation process. Several physical processes such as runoff, debris flows, granular flows, and sliding blocks falling downslope could explain the formation of these gullies. In this work, we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis. We performed a series of analogue experiments to investigate the formation of gullies on sand dune-like substrates. We used controlled flows of water over an inclined sand-box to produce gully-like forms. Ice-rich sedimentary substrates were used, including substrates that included a thin liquid water-saturated thawed layer (an ‘active layer’) above the ice-saturated zone to give an analogue for a ‘periglacial’ environment. We quantitatively demonstrate that debris flow processes in ‘periglacial’ experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels. By re-analysis of Martian elevation data for dune-gullies on Mars, we have found good evidence that such terminal deposits could exist. Our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow-length due to the subsequent reduction in infiltration capacity. Water is incorporated into the flow by erosion of the wet thawed layer (sand plus water) and by drainage of the thawed layer. Using a Mars environment simulation chamber, we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows. Our experimental investigation allowed the reproduction of terrestrial debris flow and Martian gully morphologies, suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on Mars. We suggest that, like in our laboratory experiments, the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow-length.

This study investigates the geomicrobiological potential of Upper Pleistocene evaporite deposits of the Chott el Gharsa, a wide continental sabkha in southern Tunisia. Organic and inorganic-derived biosignatures are mostly contained in microcrystalline, laminated gypsum lithofacies consisting of light/dark alternations of concordant laminae, which have precipitated from high salt concentrated waters. These biosignatures include mineralized microbial-interpreted morphologies, such as mucilage, rods, and microfibers, and dumbbell morphologies in the hollow cores of dolomite crystals that are associated with sulfates. Mineral products that are induced by microbial activity and their organic compounds lead to the formation of lenticular-shaped gypsum crystals, with a high length/width ratio, dolomite precipitation and formation of pyrite framboids. Morphological and structural aspects of these biosignatures, and their composition, in laminated, dolomite-rich sulfate deposits could be detected through microscopic investigations and micro-analyses performed by the instrumentation that is planned for ongoing Mars sample return missions.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Geological and paleobiological attributes described in a carbonate unit from the upper Silurian of the Middle Atlas (Morocco) are interpreted as the result of chemosynthetic processes fueled by fluid seepage. These attributes include: the presence of authigenic carbonate accumulation embedded in siliciclastic rocks; tightly packed, monospecific megafaunal assemblages (atrypid brachiopods); microbial-derived products; precipitation of bio-induced minerals (especially hematite); and seep-derived carbonate phases. Evidence of in-situ growth of the dense brachiopod communities is that their shells are all articulated, and show a complete range of growth sizes. Products of microbial activity are shared with other fossil seep deposits and include clotted micrite concentrations, crusts, and laminated structures, microtufts, biofilms, and endolithic filaments. The best-developed microbial features were recovered in reddish mudstone beds below and within the brachiopod concentrations, where they consist o...

The relatively unknown volcanism of the Azas Plateau in the Tuva Republic is linked with the Baikal Rift system and it presents many excellently preserved tuyas that are volcanic edifices formed by subice and underwater eruptions. These tuyas were formed in the Quaternary, when eruptions characterized by trachybasalt and basanite compositions coincided with extensive glaciation in southern Siberia. Their stratigraphy is typically composed of very thick, weak and often layered hyaloclastite sequences, and near horizontal lava cap layers produced by subaerial eruptions. The interior layered deposits (ILDs) in Valles Marineris of Mars, in general, overlie unconformably canyon floors, canyon walls, and in some cases, chaotic terrain with onlap geometry. Many of these ILD mounds have either flat-topped or domal profiles. Thin layers of a few to tens of meters in thickness are extensively observed with relatively limited post-depositional deformations, stacking up to form hundreds to possibly thousands of meters-thick sequences. One example shows possible cross-beds, but bedforms in the layers are rare within the studied MOC images. These characteristics are indicative of low-energy depositional environments such as lacustrine basins or air-falls of dust or volcanic ash rather than sediments deposited in strong currents. Volcanic sheet flows and distal facies of turbidites, however, could be also similar to some thin layers of the ILDs. The ILD mounds are also associated with possible volcanic landforms such as feeding dikes, volcanic necks and vents. Cap units, if layered, are in general near horizontal whereas lower strata could have an angular unconformity relationship with the cap layers, which can be interpreted as lava-fed deltas. These observations support the hypothesis of subice and/or underwater volcanism for the formation of the ILDs. However, not all ILDs have ideal tuya morphology and stratigraphy, implying more complex history of the ILDs in Valles Marineris. The complex interactions between rift formation, associated volcanism, ice coverage due to climate change and floods are observed in the Baikal Rift system of southern Siberia and these could be direct analogues for the Valles Marineris region of Mars.

This area of Lunae Planum (centred around 4°S and 298°E) has been studied by various authors, who have described the presence of exhumed channels (sinuous lineations), Light Layered Deposits (LLD), and detected hydrated sulphates associated with LLDs. We performed sedimentological, geomorphological, and stratigraphic analyses of the LLDs and produced geological maps of the area. The geological maps can serve as a guide for scientific or landing site analyses, and they represent a tool for making lateral correlations and for detecting different units in the vertical dimension. Our aim is to contribute to the debate about processes associated with the presence of water, the factors controlling these processes, and the residence time of liquid water on the surface of Mars. The significant element that emerges from this work is the complex evolutionary history of the study area and, to our knowledge, the area represents a unique example on Mars of clear evidence of tectonic influence on sedimentation.

A wide variety of syndepositional deformations and morphological features are related to liquefaction, and seismic shocks are one of the main causes of such deformations. On Earth, the effects of liquefaction have been observed in ancient sedimentary rocks and in surficial forms within areas affected by strong earthquakes. In terrestrial sedimentary records, analogous synsedimentary features have also been attributed to liquefaction caused by meteoritic impact (Komatsu et al. 2007, cum biblio). Moreover, processes related to meteoritic impact have been proposed as the main deformation mechanism of surficial water-saturated unlithified sediments close to impact craters on Mars. A series of coseismic ground effects produced by liquefaction was observed in the area affected by the 2012 Emilia earthquake sequence. Some of these seismic-induced features show close similarities to surficial morphological structures imaged on the Cerberus Fossae region on Mars. The aim of this study is to describe the results of terrestrial field and Martian remote observations and to discuss the geological and hydrogeological implications for the recent history of Mars.

Extensional deformations are common within foredeep basins and generally consist of hinterland-dipping normal faults located at the foredeep–foreland transition zones. Foreland-dipping normal faults at the belt–foredeep boundaries, by contrast, are far less documented and their occurrence is not predicted by simple orogenic load models. New surface data integrated with seismic reflection profiles across the Central Apennines of Italy reveal the occurrence of foreland-dipping normal faults located in the inner edges of foredeep depressions. Extensional deformations are systematically found within sequentially younger Tortonian, Messinian and Early Pliocene foredeep basins, thus suggesting that normal fault development was an intrinsic feature of the evolving belt–foredeep–foreland system and could have influenced the stratal architectures of the host syn-orogenic deposits. Foreland extension is consistent with existing geodynamic models for the Apennines and could represent the effects of lithospheric bending: its recognition and documentation elsewhere could provide significant insights to improve our understanding of syn-orogenic basin dynamics.

Outcrops of Upper Miocene to Upper Pliocene deposits in the Atlantic side of the Rifian Corridor, northwest Morocco, provide data that allow an assessment of the palaeoenvironmental evolution of the main seaway that connected the Mediterranean to the Atlantic Ocean, until its final closure at the end of the Miocene. A reconstruction of the sedimentary regimes and palaeobathymetries in the Gharb and Saiss Basins has been carried out from the physical and microfaunal (benthic foraminifera) characteristics of sediments and three sedimentary sequences are distinguished, from the oldest rocks deposited at the opening of the corridor (more than 8 Ma) to the Upper Pliocene sediments (younger than 4 Ma) that ended the marine sedimentation. The maximum palaeodepth recognised (about 500 m) occurs in marly sediments of the coastal area (Bou Regreg composite section) between 8 and 5.9 Ma. This is followed by a tectonically controlled, shallowing phase leading to the establishment of neritic conditions and corresponding to a relative sea-level lowering of about 300 m, that we suggest relates to closure of the passageway and consequent onset of the Mediterranean evaporite deposition. The persistence in the Saiss Basin of middle neritic palaeodepths since the upper Tortonian (about 7.8 Ma) suggests, for this internal basin, a sill physiography. Evidence from the present and previously documented palaeobathymetric reconstructions indicates that the tectonic activity in the Atlantic corridor started from the eastern side and moved to the west.

One of main objectives of the Mars exploration in the 21st century is to search for evidence of present or ancient life. Sedimentary processes are important on the Martian surface. However, styles of Martian sedimentation can be different from its terrestrial counterpart in some aspects because of the relatively stable Martian crust and the lack of a continuous and active surface hydrological cycle. Certain types of sedimentary deposits on Earth are closely linked to biological activities, and searching for such deposits on Mars can potentially enhance the chance of finding life or evidence of ancient life on the planet. A wide range of hypothesized siliciclastic and non-siliciclastic sedimentary deposits on Mars are of particular interest for the future exobiological exploration. Searching the substrate of sedimentary deposits is the preferred strategy because it is difficult to preserve organic matter or geochemical evidence of biological activity in the photochemically active and oxidizing surface environment of Mars.

On the surface of Titan liquids can be present in three types of environments : (i) oceans, (ii) seas and lakes, and (iii) fluvial channels. The liquid in these environments will be affected by several types of motion: progressive (tidal) waves, wind-generated waves and unidirectional currents. The physical parameters of the liquid on Titans surface can be reconstructed using the Peng–Robinson equation of state. The total energy of the waves, both tidal and wind, depends on the gravity and liquid density ; both values are lower on Titan than on Earth. Thus, the same total energy will produce larger waves on Titan. This is also valid also for the progressive waves, as it is confirmed by the physical relationship between horizontal velocity, wave amplitude, and depth of the liquid. Wind-driven waves also will tend to be larger, because the viscosity of the liquid (which is lower on Titan) controls the deformation of the liquid under shear stress. Wind-generated waves would be rather large, but the dimension of the liquid basin limits the size of the waves ; in small lakes or seas the wave power cannot reach large values. Unidirectional currents are also affected by the liquid properties. Both the relations from driving and resting forces and the Reynolds number suggests that the flows exhibit a large erosional capacity and that, theoretically, a true fluvial network could be formed. However, caution should be exercised, because the cohesion of the sedimentary interface can armour bottom and induce laterally extensive, unchanelled sheet flows with small erosional capacity.

Hydraotes Chaos is a complex basin located between the equatorial areas of chasma, east of Valles Marineris and the Chryse basin. The interactions in time and space of several sedimentary processes dominate the geological history of the chaos. The basin formed after the middle Noachian. The outflow channels related to the chaos probably flowed, during an early stage, to the south (Hydraotes channel) and to the north (Simud and Tiu Valles). After the capture of the southern Hydraotes channel by the chasma areas, the floods reversed direction and flowed northward into Hydraotes Chaos. Deltaic and lacustrine environments formed at this stage. The main consequence of the filling of the basin was the activation of Tiu Vallis. This scenario probably occurred intermittently several times during favorable climatic conditions. During these periods the water was liquid at the surface or, at least, with a frozen top layer. The major pieces of evidence for lacustrine sedimentation are: (1) terraces, (2) multiple strandlines and raised beaches, and (3) sediment drape on the basin floor. Hydraotes Chaos was the transition from the chasma areas next to Valles Marineris and the Chryse Basin. Its geological setting suggests that the water was released to Tiu Vallis episodically (during a large span of time, upper Noachian to middle Amazonian) from lakes.

The ground-penetrating radar (GPR) is a good candidate for the exploration of the Martian subsurface because it is smaller and lighter than seismic instruments, and, due to the lack of water in the Martian rocks, has great penetration capability. The modelling of the GPR signal response has been performed by computing the dielectric properties of each simulated layer as a linear function of porosity, known values of the solids, and the nature of the material filling the voids (ice water, carbou dioxide ice, gas, liquid water). The synthetic response was computed by reflecting ray-tracing at various peak frequencies. The complex results show that reflections are due to variations in mineralogy, porosity and porc-filling material. The reflectors produced by the reflection of the electromagnetic waves provide a picture of the geometries of the layers of the subsurface and give elues on the nature of rocks. Permafrost and liquid water can be investigated, chiefly their seasonal changes can be analysed by means of repeated profiles. The use of the GPR would be a major breakthrough in the reconstruction of the past geological history of the planet.

The Quaternary history of the southern Baltic is marked by a complex sequence of glacial, lacustrine and marine phases. Consequently, a large number of unconformities and erosional and depositional surfaces are present in the stratigraphic record. Over 600 km of high-resolution, single-channel reflection seismic profiles were collected offshore Bornholm. A sequence stratigraphic interpretation of the seismic data, in combination with some available core data, has led to the identification of two Quaternary depositional sequences unconformably overlying the late Mesozoic deposits. The sequences contain up to nine different seismic-stratigraphic units, and are separated by sharp boundaries representing strong erosional events. The lower depositional sequence contains five units (A-E) of glacial and late-glacial origin. The unconformity, at its base is marked by a southward flowing channel drainage pattern, which may be related to the mid-Weichselian Alnarp River system. Units A and B contain till and moraine deposits, probably of middle or early-late Weichselian age. Units C-E consist of glaciolacustrine clays, and most likely represent different Baltic Ice Lake phases of the late Weichselian. The upper depositional sequence contains four units (F-I) of postglacial lacustrine and marine origin. Its sharp erosional base possibly indicates subaerial exposure. Unit F consists of backstepping delta or beach deposits, which are partially interfingered with the lacustrine clays of unit G. Both units can most likely be correlated with the Ancylus Lake. The marine mud deposits of units H and I represent the widespread Litorina transgression.

The Po Plain is a molasse foredeep bounded by two mountain chains: Apennines and Alps. Apenninic thrusting is still active, whereas the Alpine one ended by Early Pliocene times. The continental deposits form a veneer at the surface and form the topset of a prograding complex. The Po River divides the plain into two sectors with different sedimentary facies and body geometries. To the south, the alluvial fan and plain deposits are small, embedded in clays, and show elongate shapes. To the north, sedimentary bodies are laterally extensive, tabular and with minor amounts of fine-grained sediments. This difference could be due to: (a) different climatic conditions during Quaternary ice ages on the two sides of the basin; (b) different structural settings in the two sectors of the basin, that produce a higher subsidence rate to the south; (c) different lithologies in the source areas (i.e. Alps and Apennines).

[1] In this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in Nili Patera on Mars. The measured average migration of ∼1.7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area. In addition, we document widespread changes in the dune base-ground surface contact and in the slip face structures, showing that not only the ripples, but the whole dunes are actually migrating in the present-day atmospheric setting. These results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on Mars may also be active.

International audience; In this paper we present the findings of a COSPAR Mars Special Regions Colloquium held in Rome in 2007. We review and discuss the definition of Mars Special Regions, the physical parameters used to define Mars Special Regions, and physical features on Mars that can be interpreted as Mars Special Regions. We conclude that any region experiencing temperatures > -25 degrees C for a few hours a year and a water activity > 0.5 can potentially allow the replication of terrestrial microorganisms. Physical features on Mars that can be interpreted as meeting these conditions constitute a Mars Special Region. Based on current knowledge of the martian environment and the conservative nature of planetary protection, the following features constitute Mars Special regions: Gullies and bright streaks associated with them, pasted-on terrain, deep subsurface, dark streaks only on a case-by-case basis, others to be determined. The parameter definition and the associated list of physical features should be re-evaluated on a regular basis.

The large family of dry lakes includes a variety of morphologies, types of surfaces, facies, and sedimentary structures where the evaporation of water plays a major role. To describe them, the term sabkha is largely used in the literature. The sedimentation at the margin of dry lakes is dominated by mechanical deposition of siliciclastic detritus that form the background for chemical or biochemical deposition of mostly sulfates and carbonates. The sabkha's environment is a sink for both evaporitic and siliciclastic sediments. In addition to the lacustrine-related processes, fluvial and eolian activity plays an important role in providing sediment and in modeling the environment that need to be considered in the formation and evolution of sabkhas. Shorelines are subtle in the driest sabkhas because they are rarely inundated and wave action cannot build appreciable fronts and terraces. Mud flats are actually dominated by evaporitic sedimentation such as those active in saline lakes that occupy the hydrological lows of basins. The presence of abundant sulfate minerals has been confirmed by a number of recent Mars missions from both orbit and surface as well as exposures of carbonates. The existence of dry lakes on Mars consistent with the morphological and mineralogical record suggests that the planet experienced a large-scale hydrological cycle involving both ground and surface water. A potential candidate of sabkha on Mars is the Columbus crater in Terra Sirenum where data support the presence of evaporitic sulfates and clays.

71 manuscript pages, 12 figures, 3 tables.-- Presented at the 2nd International Workshop on Exploring Mars and its Earth Analogues, Trento, Italy, June 19-23, 2007: http://digital.csic.es/handle/10261/8617, The Gamma Ray Spectrometer (Mars Odyssey spacecraft) has revealed elemental distributions of potassium (K), thorium (Th), and iron (Fe) on Mars that require fractionation of K (and possibly Th and Fe) consistent with aqueous activity. This includes weathering, evolution of soils, and transport, sorting, and deposition, as well as with the location of first-order geomorphological demarcations identified as possible paleoocean boundaries. The element abundances occur in patterns consistent with weathering in situ and possible presence of relict or exhumed paleosols, deposition of weathered materials (salts and clastic minerals), and eathering/transport under neutral to acidic brines. The abundances are explained by hydrogeology consistent with the possibly overlapping alternatives of paleooceans and/or heterogeneous rock compositions from diverse provenances (e.g, differing igneous compositions)., We are grateful to the Gamma Ray Spectrometer Team whose diligent efforts have yielded tremendous fruit. Kyeong Kim is partially supported by the Basic Research Project (08-3611) of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science and Technology (MOST) of Korea.

We studied north Tyrrhena Terra, an approximately 39,000 km2 area, located in the transition region straddling the Amenthes and Mare Tyrrhenum Mars Chart quadrangles 14 and 22, respectively. The study area comprises ancient terrains with infilled craters, ridges and valleys. Interpretation of orbiter data of ancient terrains is inherently difficult, but valuable information can be obtained using multiple datasets and analyzing various geological features. Using data from the High Resolution Stereo Camera on board Mars Express, complemented by Mars Global Surveyor MOLA DEM and MOC Narrow Angle datasets, we observed and interpreted surface morphologies at a scale suitable for geologic investigation. Morphometric examination of a 31 km diameter large impact crater indicated that tectonism and volcanism were responsible for its morphologic modification. Small impact crater depth/diameter relationships indicated that smooth surfaces of valleys are composed of highly consolidated material. Surface cracks and lobate fronts further suggested that the rocks are volcanic. Examination of tectonic features revealed that in the study area: a dominant NW-SE fabric is related to a ridge/bench-scarp-valley repetition consistent with synthetic and antithetic normal faulting; a NNW-SSE lineament represents the surface expression of normal faulting post-dating all other tectonic features. A weak NE-SW fabric is observable as small sublinear depressions, and at the contact between units internal to one large crater. One 20 km diameter crater in the study area was interpreted to be a caldera, infilled by thick volcanic rock layers. Identification of wrinkle ridges further indicated that thick layered lava flows infilled the main depressions of the study area. The available evidence suggests that the study area underwent multiple episodes of extension and volcanism. © 2007 Elsevier Inc. All rights reserved.

[1] The Life in the Atacama project examined six different sites in the Atacama Desert (Chile) over 3 years in an attempt to remotely detect the presence of life with a rover. The remote science team, using only orbital and rover data sets, identified areas with a high potential for life as targets for further inspection by the rover. Orbital data in the visible/near infrared (VNIR) and in the thermal infrared (TIR) were used to examine the mineralogy, geomorphology, and chlorophyll potential of the field sites. Field instruments included two spectrometers (VNIR reflectance and TIR emission) and a neutron detector: this project represents the first time a neutron detector has been used as part of a “science-blind” rover field test. Rover-based spectroscopy was used to identify the composition of small scale features not visible in the orbital images and to improve interpretations of those data sets. The orbital and ground-based data sets produced consistent results, suggesting that much of the field sites consist of altered volcanic terrains with later deposits of sulfates, quartz, and iron oxides. At one location (Site A), the ground-based spectral data revealed considerably greater compositional diversity than was seen from the orbital view. One neutron detector transect provided insight into subsurface hydrogen concentrations, which correlated with life and surface features. The results presented here have implications for targeting strategies, especially for future Mars rover missions looking for potential habitats/paleohabitats.

[1] An intravalley paleolake (more than 400 m deep) was detected along the course of Shalbatana Vallis from the evidence of shorelines and the occurrence of a few fan-delta deposits (including a Gilbert-type delta). The fronts of all the sedimentary deposits strikingly match the same topographic contours (2800 and 3000 m below the Martian datum), indicating the paleolake water levels under which they formed. Also, the corresponding shorelines are visible along the Shalbatana Vallis walls. The peculiar settings of the lake suggest that Shalbatana Vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system. Water source is uncertain, but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate, transport, and deposit the materials found in the deposits. Previous works and new crater counting computations indicate that the paleolake was active during the Hesperian epoch; therefore, at that time, surface conditions were different from those of modern Mars and supportive of flow and ponding of water. It is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism, impact cratering, and tectonism could have also triggered/accelerated the local groundwater activity, implying that the system could have evolved relatively independent from climatic conditions. The latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about Martian climatic-geomorphological evolution.