27 research outputs found
Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge
Groundâbased bedding orientation measurements are critical to determine the geologic history and processes of sedimentation in Gale crater, Mars. We constrain the dip of lacustrine strata of the Blunts Point, Pettegrove Point, and Jura members of the Murray formation using a combination of regional stratigraphic correlations and bed attitude measurements from stereo Mastcam images taken by the Mars Science Laboratory Curiosity rover. In situ bed attitude measurements using a principal component analysisâbased regression method reveal a wide range of dips and dip azimuths owing to a combination of high stereo errors, postdepositional deformation of strata (e.g., fracturing, rotation, and impact cratering), and different primary depositional dips. These constrain regional dips to be within several degrees of horizontal on average. Stratigraphic correlations between targets observed in the Glen Torridon trough and at the Pettegrove PointâJura member contact of Vera Rubin ridge (VRR) constrain dips to be between 3°SE and 2°NW, consistent with nearly flat strata deposited horizontally on an equipotential surface. The Jura member is determined to be stratigraphically equivalent to the northern portion of the Glen Torridon trough. Roverâbased dip magnitudes are generally significantly shallower than the orientation of VRR member contacts measured from High Resolution Imaging Science Experimentâbased traces, suggesting the sedimentary strata and VRR member contacts may be discordant
Extraformational sediment recycling on Mars
Extraformational sediment recycling (old sedimentary rock to new sedimentary rock) is a fundamental aspect of Earth's geological record; tectonism exposes sedimentary rock, whereupon it is weathered and eroded to form new sediment that later becomes lithified. On Mars, tectonism has been minor, but two decades of orbiter instrument-based studies show that some sedimentary rocks previously buried to depths of kilometers have been exposed, by erosion, at the surface. Four locations in Gale crater, explored using the National Aeronautics and Space Administration's Curiosity rover, exhibit sedimentary lithoclasts in sedimentary rock: At Marias Pass, they are mudstone fragments in sandstone derived from strata below an erosional unconformity; at Bimbe, they are pebble-sized sandstone and, possibly, laminated, intraclast-bearing, chemical (calcium sulfate) sediment fragments in conglomerates; at Cooperstown, they are pebble-sized fragments of sandstone within coarse sandstone; at Dingo Gap, they are cobble-sized, stratified sandstone fragments in conglomerate derived from an immediately underlying sandstone. Mars orbiter images show lithified sediment fans at the termini of canyons that incise sedimentary rock in Gale crater; these, too, consist of recycled, extraformational sediment. The recycled sediments in Gale crater are compositionally immature, indicating the dominance of physical weathering processes during the second known cycle. The observations at Marias Pass indicate that sediment eroded and removed from craters such as Gale crater during the Martian Hesperian Period could have been recycled to form new rock elsewhere. Our results permit prediction that lithified deltaic sediments at the Perseverance (landing in 2021) and Rosalind Franklin (landing in 2023) rover field sites could contain extraformational recycled sediment.With funding from the Spanish government through the "MarĂa de Maeztu Unit of Excellence" accreditation (MDM-2017-0737
Curiosity at Vera Rubin Ridge: Major Findings and Implications for Habitability
No abstract availabl
The Akilia Controversy: field, structural and geochronological evidence questions interpretations of >3.8 Ga life in SW Greenland
<p>Field relations, structure and geochronology demonstrate that controversial rocks on Akilia, SW Greenland, cannot host evidence
of Earth's oldest life. Maficâultramafic gneiss that contains a layer of quartzâamphiboleâpyroxene gneiss, a few metres thick,
with purported biogenic graphite is not cross-cut by the protoliths of >3.82â3.65 Ga tonalitic gneiss. The contact between
these gneisses is tectonic so their relative ages are unknown. Multiple episodes of intrusion and deformation in the tonalitic
gneiss preceded the earliest deformation fabrics and structures seen in the maficâultramafic gneiss. Although previously interpreted
as a volcano-sedimentary stratigraphy, the maficâultramafic gneiss displays no evidence of such an origin, and could be partly
or wholly derived from igneous intrusions. Existing geochronology indicates that the maficâultramafic and qtzâamâpx gneisses
have ages <3.67 Ga. Metamorphic zircon in the qtzâamâpx gneiss grew at <em>c</em>. 2.68 Ga during late Archaean high-grade events that complicate any protolith interpretation. UâPb dating of apatite from
a variety of rocks on Akilia shows that this mineral crystallized, or possibly recrystallized, at <em>c</em>. 1.75 Ga and it thus provides no indication of an early Archaean age for any associated graphite, regardless of whether or
not the latter is biogenic.
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Geological constraints on detecting the earliest life on Earth: a perspective from the Early Archaean (older than 3.7âGyr) of southwest Greenland
At greater than 3.7âGyr, Earth's oldest known supracrustal rocks, comprised dominantly of mafic igneous with less common sedimentary units including banded iron formation (BIF), are exposed in southwest Greenland. Regionally, they were intruded by younger tonalites, and then both were intensely dynamothermally metamorphosed to granulite facies (the highest pressures and temperatures generally encountered in the Earth's crust during metamorphism) in the Archaean and subsequently at lower grades until about 1500âMyr ago. Claims for the first preserved life on Earth have been based on the occurrence of greater than 3.8âGyr isotopically light C occurring as graphite inclusions within apatite crystals from a 5âm thick purported BIF on the island of Akilia. Detailed geologic mapping and observations there indicate that the banding, first claimed to be depositional, is clearly deformational in origin. Furthermore, the mineralogy of the supposed BIF, being dominated by pyroxene, amphibole and quartz, is unlike well-known BIF from the Isua Greenstone Belt (IGB), but resembles enclosing mafic and ultramafic igneous rocks modified by metasomatism and repeated metamorphic recrystallization. This scenario parsimoniously links the geology, whole-rock geochemistry, 2.7âGyr single crystal zircon ages in the unit, an approximately 1500âMyr age for apatites that lack any graphite, non-MIF sulphur isotopes in the unit and an inconclusive Fe isotope signature. Although both putative body fossils and carbon-12 enriched isotopes in graphite described at Isua are better explained by abiotic processes, more fruitful targets for examining the earliest stages in the emergence of life remain within greater than 3.7âGyr IGB, which preserves BIF and other rocks that unambiguously formed at Earth's surface
Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge
Groundâbased bedding orientation measurements are critical to determine the geologic history and processes of sedimentation in Gale crater, Mars. We constrain the dip of lacustrine strata of the Blunts Point, Pettegrove Point, and Jura members of the Murray formation using a combination of regional stratigraphic correlations and bed attitude measurements from stereo Mastcam images taken by the Mars Science Laboratory Curiosity rover. In situ bed attitude measurements using a principal component analysisâbased regression method reveal a wide range of dips and dip azimuths owing to a combination of high stereo errors, postdepositional deformation of strata (e.g., fracturing, rotation, and impact cratering), and different primary depositional dips. These constrain regional dips to be within several degrees of horizontal on average. Stratigraphic correlations between targets observed in the Glen Torridon trough and at the Pettegrove PointâJura member contact of Vera Rubin ridge (VRR) constrain dips to be between 3°SE and 2°NW, consistent with nearly flat strata deposited horizontally on an equipotential surface. The Jura member is determined to be stratigraphically equivalent to the northern portion of the Glen Torridon trough. Roverâbased dip magnitudes are generally significantly shallower than the orientation of VRR member contacts measured from High Resolution Imaging Science Experimentâbased traces, suggesting the sedimentary strata and VRR member contacts may be discordant