A deep subaqueous fan depositional model for the Palaeoarchaean (3.46 Ga) Marble Bar Cherts, Warrawoona Group, Western Australia

International audienceThe 3.46 Ga Marble Bar Chert Member of the East Pilbara Craton, Western Australia, is one of the earliest and best-preserved sedimentary successions on Earth. Here, we interpret the finely laminated thin-bedded cherts, mixed conglomeratic beds, chert breccia beds and chert folded beds of the Marble Bar Chert Member as the product of low-density turbidity currents, high-density turbidity currents, mass transport complexes and slumps, respectively. Integrated into a channel-levee depositional model, the Marble Bar Chert Member constitutes the oldest documented deep-sea fan on Earth, with thin-bedded cherts, breccia beds and slumps composing the outer levee facies tracts, and scours and conglomeratic beds representing the channel systems

The mineral diversity of Jezero crater: Evidence for possible lacustrine carbonates on Mars

Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the “Marginal Carbonates,” located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars

Mars Sedimentary Geology: Key Concepts and Outstanding Questions

Processes that operate at planetary surfaces have the potential to record a history of planetary evolution in the form of sedimentary rocks. This is important because our experience on Earth shows that sediments and sedimentary rocks are the dominant archive of high-resolution proxies of present and past tectonic, climatic, and biological processes. Our understanding of the evolution of Earth’s very ancient climate and paleobiological records derives from detailed examination of the mineralogical, textural, and geochemical signatures preserved in the sedimentary rock record. Sedimentary rocks were first recognized on Mars less than a decade ago (Malin and Edgett, 2000). Recent interpretations of data collected by the Mars Express and Mars Reconnaissance Orbiter spacecraft have confirmed the surprising abundance of these sedimentary rocks, the past role of water on the martian surface, and the similarity—in some cases—to sedimentary rocks formed on Earth. Thick sulfaterich deposits invite comparison to terrestrial evaporites (Grotzinger et al., 2005). In other cases, clay-rich strata are interpreted as the terminal deposits of source-to-sink systems with well-developed fluvial networks in the upper reaches of watersheds that date back to a much wetter period in Mars’ earliest history (Ehlmann et al., 2008; Metz et al., 2009). However, these Earth-like depositional systems contrast with other deposits that may be unique in the Solar System: for example, vast terrains as large as Earth’s continents covered by thick veneers of strata that may derive entirely from settling out of wind-transported dust (Bridges et al., 2010). Whatever their origin, it is now clear that the sedimentary rocks of Mars represent a new frontier for research. Mars science is in its golden era of exploration—the past decade of orbiter and landed missions has produced an extraordinary amount of new data relevant to the analysis of sediments and sedimentary rocks, and robust international programs exist for future missions. To help stimulate discussion of these data, the First International Conference on Mars Sedimentology and Stratigraphy was convened in El Paso, Texas, in April 2010. The contents of this white paper represent the most significant findings of the conference, with additional information provided by the coauthors, and focus on seven key questions for future investigation by the sedimentary geology community

The SuperCam Remote Sensing Instrument Suite for Mars 2020

International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

SuperCam Calibration Targets: Design and Development

SuperCam is a highly integrated remote-sensing instrumental suite for NASA’s Mars 2020 mission. It consists of a co-aligned combination of Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), Visible and Infrared Spectroscopy (VISIR), together with sound recording (MIC) and high-magnification imaging techniques (RMI). They provide information on the mineralogy, geochemistry and mineral context around the Perseverance Rover. The calibration of this complex suite is a major challenge. Not only does each technique require its own standards or references, their combination also introduces new requirements to obtain optimal scientific output. Elemental composition, molecular vibrational features, fluorescence, morphology and texture provide a full picture of the sample with spectral information that needs to be co-aligned, correlated, and individually calibrated. The resulting hardware includes different kinds of targets, each one covering different needs of the instrument. Standards for imaging calibration, geological samples for mineral identification and chemometric calculations or spectral references to calibrate and evaluate the health of the instrument, are all included in the SuperCam Calibration Target (SCCT). The system also includes a specifically designed assembly in which the samples are mounted. This hardware allows the targets to survive the harsh environmental conditions of the launch, cruise, landing and operation on Mars during the whole mission. Here we summarize the design, development, integration, verification and functional testing of the SCCT. This work includes some key results obtained to verify the scientific outcome of the SuperCam system

Faciès grumeleux, noduleux et cryptalgaires des marges jurassiques de la Tethys nord-occidentale et de l'Atlantique central : genèse, paléoenvironnements et géodynamique associée

Nodular Ammonitico-Rosso lithofaciès which characterize the differentiation or Jurassic continental margins were investigated. The basic aim was to resolve the identity or carbonate ‘’lumps’’ and nodules and to understand their genesis, to determine the depositional environments and to show their relation with the geodynamic evolution or the margins. The early discovery or accompanying cryptalgal fabrics caused and additional and more specific survey to be carried out. Since the studied sites correspond to either in situ drowned margins (Atlantic) or exhumed ones (Tethys), they are expected to yield complementary information.As preliminary note is the typology of encountered carbonate elements and textures.The first part concerns the Oxfordian ‘’lumpy’’ and nodular pelagic limestones extending along the ‘’vivaro-cevenole’’ border (South-East France ; nortwestern Tethyan margin). The bathymetry trend, joined to successive facies distribution and restored isopachs, permit understanding of the Callovian-Oxfordian tectonic activity and of the basal unconformity origin. This records a definite deepening and is assumed to occur in response to an original lack or sediments. Much similar occurrences of cryptalgal developments have been recognized in coeval layers of the Southern Subalpine ranges (France). Those examined on the Trento Plateau in Northern Italy yield slight differences.The second part regards deep sea drilling (DSDP) along the central Atlantic eastern margin. The chief aim is to resolve the genesis or recovered nodules. DSDP Site 547 is located off Morocco (Mazagan Escarpment) in a subbasin upon continental basement. Stromatolitic crusts have been recorded from core inspections throughout the Jurassic pelagic limestones.DSDP site 367 (Cape Verde Basin) yields Upper Jurassic nodular limestones overlying an oceanic crust. Several types of textures have been distinguished. The original alternating setting of deposits, the winnowing and the sliding caused by the basement instability are thought to have induced their genesis. This rhythmical enrichment with radiolarians and the origin or the silica are debated. The depositional depth is estimated and the basaltic floor is tentatively assigned to the boundary lower-middle Oxfordian. Filament microfacies are believed to be Kimmeridgian in age, from a comparison with other central Atlantic DSDP sites. Comparisons with similar Tethyan nodular formations have been performed as well. The control on radiolaritic sedimentation is discussed.The third part deals with Upper Jurassic cryptalgal lithofacies cored in the Abenaki Formation (Baccaro Member) on the Scotian paleoshelf edge off eastern Canada (oil exploratory wells). Carbonate buildups were constructed by thrombolite-stromatolite-annelid-Tubiphytes communities.Genetic factors of the Ammonitico Rosso lithofacies are reviewed and graded.The nature of the fine carbonate Jurassic sediment seems to be the main factor.AR are no reliable geodynamic markers but have rather to be related to sedimentary events. Cryptalgal fabric could develop in quite deep-water environments without requiring any light.Les lithofaciès de type Ammonitico Rosso sont analysés. L’objectif est de connaître l’origine des grumeaux et des nodules, de reconstituer les environnements et d’intégrer ces formations dans l’évolution géodynamique des marges. La découverte de structures cryptalgaires associées a motivé une étude plus spécifique. Les sites étudiés appartiennent à des marges en place et ennoyées (Atlantique) ou exhumées (Téthys) et livrent des informations complémentaires.La première partie se rapporte aux faciès grumeleux et noduleux oxfordiens de la bordure vivaro-cévenole (bassin du Sud-Est ; marge nord-téthysienne). Des corps cryptalgaires diversifiés surmontent une discontinuité majeure. L’alternance argilo-carbonatée superposée renferme des grumeaux liés à la bioturbation et des moules d’ammonoïdes. Des environnements marins profonds sont déduits des données paléoécologiques et des reconstructions palinspastiques et régionales. L’évolution bathymétrique jointe à la distribution et à la puissance des faciès nous renseignent sur la géodynamique callovo-oxfordienne et sur l’origine de la discontinuité basaleLa deuxième partie concerne les forages DSDP de la marge orientale de l’Atlantique central. Le site 547 est situé au large du Maroc (Escarpement de Mazagan) dans un sous bassin épicontinental. Les croûtes stromatolitiques, les remobilisations gravitaires, la bioturbation et le vannage sont responsables de la genèse des textures dans les calcaires pélagiques. Le site DSDP 367 (bassin du Cap Vert) a fourni des calcaires noduleux du Jurassique supérieur qui surmontent une croûte océanique. La disposition alternante des dépôts, enrichis de manière rythmique en radiolaires, et l’instabilité tectonique ont engendré plusieurs types de textures.La troisième partie est consacrée aux faciès cryptalgaires du Jurassique supérieur carottés dans l’Abenaki Formation sur le bord externe du plateau scotian au large du Canada oriental. Des thrombolites et stromatolites sont engagés dans des constructions d’eaux profondes. Leur mode d’édification, l’évolution de cavités et le cadre tectonique sont présentés.Les facteurs controlant dans la genèse des Ammonitico Rosso sont recensés et hiérarchisés. La nature des sédiments jurassique semble jouer un rôle déterminant. Les AR ne sont pas des marqueurs géodynamiques précis mais représentent des évènements sédimentaires. Les constructions cryptalgaires peuvent se développer dans des milieux assez profonds (100’s m) sans exiger la présence de lumière

Évolution des eaux ouest-téthysiennes (température, bathymétrie) au cours du Jurassique moyen à supérieur à partir des enregistrements géochimques (d18O, d13C, REE) de faunes marines

Les différences de d18O entre brachiopodes benthiques et vertébrés de surface sont utilisés pour reconstituer les variations de température à différentes profondeurs dans les eaux tropicales ouest-thétysiennes jurassiques. Une courbe continue (+- 1 Ma) de l'évolution des températures de surface (poissons) à l'est du bassin de Paris est proposée de l'Aalénien au Tithonien avec un d18O de l'eau de -1 % pour un océan sans glace. Des fluctuations de 2-3 C en moyenne en 2-3 Ma sont observées, notamment un refroidissement à la limite Callovien-Oxfordien (24C à 17 C), synchrone de l'installation d'ammonites boréales. La cohérence des marqueurs paléothermométriques, isotopiques et paléontologiques, à différentes latitudes prouve le caractère global du refroidissement. Les températures isotopiques trop faibles de l'Oxfordien inf. indiqueraient une glaciation (d18Oeau > -1). Les changements thermiques seraient initiés par le volcanisme aérien au Bajocien/Bathonien (réchauffement de 20 à 24 C) et par le stockage de matière organique au Callovien moyen. On note aussi des variations régionales ouest/est, avec à l'ouest un paléocourant froid boréal (Bathonien) et des valeurs de d13C des brachiopodes jurassiques inférieures de 1 pour mille par rapport à l'est, expliquées par une quantité de matière organique oxydée supérieure (2 masses d'eau ?). D'autre part, les spectres de terres rares des dents provenant de carbonates sont représentatifs des eaux de plate-forme ouest-thétysiennes avec un appauvrissement en terres rares lourdes quantifié par le rapport (Dy/Yb)n. Les rapports (Dy/Yb)n augmentent de 1 à 5 avec la profondeur alors qu'ils diminuent actuellement (0,9 à 0,8). Ce soutirage progressif, efficace des terres rares lourdes serait du à des porteurs primaires différents de l'actuel, similaires au Paléozoïque. Des gammes de températures (0-12C) et des paléoprofondeurs (0-200 m) du bassin sont estimées à partir des écarts isotopiques entre brachiopodes et poissons et des rapports (Dy/Yb).LYON1-BU.Sciences (692662101) / SudocSudocFranceF