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

Weathering in the Forelands of Two Rapidly Retreating Alpine Glaciers of Volcanic Bedrock in the Three Sisters, Oregon, USA

The glaciers of the Three Sisters volcanoes in Cascadia have retreated dramatically over the past century. In order to understand ongoing chemical weathering and solute transport in the proglacial valleys, waters were sampled from glacier outwash streams, local snowmelt, and proglacial springs and lakes at Collier and Diller Glaciers. To understand weathering and transport processes in the proglacial plains, infrared orbital remote sensing data was used to map compositional variability and highlight weathering products, which were then ground-truthed with laboratory mineralogical and chemical analyses of sediments. The hydrochemistry is significantly affected by a sub- and proglacial mafic weathering system lacking carbonate minerals. Here we report major ion concentrations in meltwaters for the summer 2016 and 2017 melt seasons. Total cation concentrations range from 3 to 250 eq/l and dissolved bicarbonate concentrations range from 2 to 200 eq/l. Other dissolved anions are negligible compared to bicarbonate. Dissolved silica concentrations range from 2 to 260 mol/l, comparable to total dissolved cation concentrations. The highest cation and silica concentrations were measured in moraine-sourced springs. Compositional remote sensing analysis identified alteration zones in the proglacial plains at both Collier and Diller indicating potential hydrated silica. This analysis is consistent with laboratory analysis of sediment samples, which indicate the presence of poorly crystalline phases weathering products, including hydrated silica. Weathered materials are preferentially deposited on moraines due to aeolian and glacial transport, as well as intra-moraine alteration, and at abandoned stream terraces due to fluvial transport. Geochemical measurements indicate that the predominant form of chemical weathering in these periglacial mafic systems is the carbonation of feldspar as well as reactive volcanic glass. The presence of poorly crystalline silicates, as indicated by remote sensing datasets and laboratory analysis, is consistent with rapid weathering of feldspars and glass and formation of Fe-Al-Si-bearing mineraloids in these proglacial valleys. This weathering regime has wide-ranging implications for atmospheric CO2 drawdown due to cold-climate volcanic rock weathering

Joint M3 and Diviner Analysis of the Mineralogy, Glass Composition, and Country Rock Content of Pyroclastic Deposits in Oppenheimer Crater

Here we present our analysis of the near- and mid-infrared spectral properties of pyroclastic deposits within the floor fractured Oppenheimer Crater that are hypothesized to be Vulcanian in origin. These are the first results of our global study of lunar pyroclastic deposits aimed at constraining the range of eruption processes on the Moon. In the near-infrared, we have employed a new method of spectral analysis developed in Horgan et al. (2013) of the 1 m iron absorption band in Chandrayaan-1 Moon Mineralogy Mapper (M3) spectra. By analyzing both the position and shape of the 1 m band we can detect and map the distribution of minerals, glasses, and mixtures of these phases in pyroclastic deposits. We are also using mid-infrared spectra from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment to develop ~200 m/pixel Christiansen Feature (CF) maps, which correlate with silica abundance. One of the benefits of using CF maps for analysis of pyroclastic deposits is that they can be used to detect silicic country rock that may have been emplaced by Vulcanian-style eruptions, and are sensitive to iron abundance in glasses, neither of which is possible in the near-infrared. M3 analysis reveals that the primary spectral endmembers are low-calcium pyroxene and iron-bearing glass, with only minor high-calcium pyroxene, and no detectable olivine. The large deposit in the south shows higher and more extensive glass concentrations than the surrounding deposits. We interpret the M3 spectra of the pyroclastic deposits as indicating a mixture of low-calcium pyroxene country rock and juvenile glass, and no significant olivine. Analysis of Diviner CF maps of the Oppenheimer crater floor indicates an average CF value of 8.16, consistent with a mixture of primarily plagioclase and some pyroxene. The average CF values of the pyroclastic deposits range from 8.31 in the SW to 8.24 in the SE. Since CF values within the deposits are as high as 8.49, the lower average CF values of the deposits suggest that each deposit is a mixture of crater floor material and highly mafic juvenile material consistent with either olivine or Fe-bearing pyroclastic glass. Synthesizing our M3 and Diviner results indicates that the crater floor consists of plagioclase with some pyroxene, and the pyroclastic deposits are a mix of this substrate and a glass-rich juvenile material. While we cannot determine the iron content of the glass from M3 spectra alone, the high Diviner CF values suggest that the glass is relatively iron-rich. Indeed, FeO abundances inferred from CF values using the method of Allen et al. (2012) imply that the large southern deposit exhibits a significant enhancement in iron content. This supports our hypothesis that the glass in this deposit is relatively iron-rich

Deriving Amorphous Component Abundance and Composition of Rocks and Sediments on Earth and Mars

International audiencePlain Language Summary X-ray amorphous materials have been detected in all samples measured by the CheMin X-ray diffractometer (XRD) on board the Mars Science Laboratory rover in Gale Crater, Mars. The origin(s) of these materials are poorly understood, and there are significant uncertainties on their estimated abundances and compositions. Three methods are used to estimate the bulk amorphous component abundance and composition of Martian samples using XRD and bulk chemical data: (1) Rietveld refinements, (2) FULLPAT analyses, and (3) mass balance calculations. We tested these methods against a quantitative XRD (internal standard) method commonly used in terrestrial laboratories. Additionally, we tested for instrumentation effects by measuring our samples on a laboratory XRD instrument (PANalytical X'Pert Pro) and the CheMin test bed instrument (CheMin IV). We used three natural samples known to contain amorphous materials: glacial sediment, Hawaiian soil, and a paleosol. Our methods resulted in nine amorphous abundances and four amorphous compositions for each sample. For a single sample, amorphous abundance estimates and amorphous compositions are relatively similar across all estimation methods. CheMin analog measurements perform well in our tests, with amorphous abundances and compositions comparable to laboratory quantitative XRD measurements, though slightly underestimated. This suggests that previous amorphous component estimates for Martian samples are relatively accurate. This study highlights the usefulness of the mass balance calculation method for characterizing amorphous materials in terrestrial samples, providing important supplemental information to destructive and time consuming size separation and dissolution procedures. Natural soil and sediment samples on Earth and Mars are commonly mixtures of crystalline and noncrystalline materials. X-ray diffraction techniques are frequently used to quantify the abundance and composition of crystalline materials, and relatively recent developments in X-ray diffraction data analysis methods allow noncrystalline materials to also be characterized. Noncrystalline materials are studied using the following methods: (1) noncrystalline X-ray diffraction peaks modeled with broad peaks, (2) noncrystalline peaks modeled with diffraction patterns of measured noncrystalline materials, and (3) a mass balance calculation that combines chemical and X-ray diffraction data. However, it is uncertain how accurate these methods are. Here we systematically test these three data analysis methods on complex natural samples. We find that both modeling methods (1 and 2) are capable of providing relatively accurate noncrystalline component abundances. Modeling noncrystalline peaks with patterns of measured noncrystalline materials (method 2) provides the most accurate abundance results but does not necessarily provide accurate compositional information, whereas the mass balance calculation provides accurate noncrystalline material compositions, but not abundances. Our results suggest that a combination of methods (either 1 and 3 or 2 and 3) should be used to more completely characterize the abundance and composition of noncrystalline materials

DEPOSITIONAL HYPOTHESES FOR THE EMPLACEMENT OF THE MARGIN UNIT, JEZERO CRATER, MARS

International audienceAfter 910 sols, the Mars 2020 Perse-verance rover has begun exploring the margin unit, the region with the strongest and clearest orbital signature of carbonate minerals (Figure1) [1, 2]. Stratigraphically, the margin unit is older than the Upper Delta/Fan Top units and lies unconformably below curved and inclined sandstone deposits, interpreted as fluvial deposits, and below the boulder-rich unit (Figure 2). On Mars, rovers and orbiters have only detected carbonates in trace amounts in only a few locations on the surface [3]; how-ever, their sources are primarily unclear. Some car-bonate material is also found in martian meteorites such as ALH 84001 and Nakhla [3]. The sources are aqueous alteration of igneous material, both in Comanche rock and ALH84001 [3]. Carbonates generally form due to aqueous processes in solutions that contain inorganic carbon. However, the meteorites do not preserve a rec-ord of specific surface processes in past habitable envi-ronments. Based on orbital detections, the carbonate material in Jezero is hypothesized to have precipitated from a lacustrine environment [1]

DEPOSITIONAL HYPOTHESES FOR THE EMPLACEMENT OF THE MARGIN UNIT, JEZERO CRATER, MARS

International audienceAfter 910 sols, the Mars 2020 Perse-verance rover has begun exploring the margin unit, the region with the strongest and clearest orbital signature of carbonate minerals (Figure1) [1, 2]. Stratigraphically, the margin unit is older than the Upper Delta/Fan Top units and lies unconformably below curved and inclined sandstone deposits, interpreted as fluvial deposits, and below the boulder-rich unit (Figure 2). On Mars, rovers and orbiters have only detected carbonates in trace amounts in only a few locations on the surface [3]; how-ever, their sources are primarily unclear. Some car-bonate material is also found in martian meteorites such as ALH 84001 and Nakhla [3]. The sources are aqueous alteration of igneous material, both in Comanche rock and ALH84001 [3]. Carbonates generally form due to aqueous processes in solutions that contain inorganic carbon. However, the meteorites do not preserve a rec-ord of specific surface processes in past habitable envi-ronments. Based on orbital detections, the carbonate material in Jezero is hypothesized to have precipitated from a lacustrine environment [1]