Geology topics

Christopher M. Fedo

Publications and source records attributed to Christopher M. Fedo.

13 recordsLinked to original sources

USGS2024

Evolution of a lake margin recorded in the Sutton Island member of the Murray formation, Gale crater, Mars

This study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar-laminated mudstone with minor intervals of planar sandstone, ripple cross-laminated sandstone, cross-stratified sandstone, and alternating laminated sandstone and mudstone. Meter-thick packages of planar-laminated mudstone in FA1 are interpreted to represent deposition in low-energy ponded environments along the lake margin. Straight- and curve-crested ripple cross-laminated facies are interpreted to represent current-influenced deposition. Cross-stratified sandstone facies consist of dm-thick sets that represent deposition in distal channels. Intercalated mm-scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar-laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine-basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater.

Journal of Geophysical Research - Planets↗

USGS2022

The Curiosity Rover’s exploration of Glen Torridon, Gale crater, Mars: An overview of the campaign and scientific results

The Mars Science Laboratory rover, Curiosity , explored the clay mineral-bearing Glen Torridon region for one martian year between January 2019 and January 2021, including a short campaign onto the Greenheugh pediment. The Glen Torridon campaign sought to characterize the geology of the area, seek evidence of habitable environments, and document the onset of a potentially global climatic transition during the Hesperian era. Curiosity roved 5 km in total throughout Glen Torridon, from the Vera Rubin ridge to the northern margin of the Greenheugh pediment. Curiosity acquired samples from 11 drill holes during this campaign and conducted the first martian thermochemolytic-based organics detection experiment with the Sample Analysis at Mars instrument suite. The lowest elevations within Glen Torridon represent a continuation of lacustrine Murray formation deposits, but overlying widespread cross bedded sandstones indicate an interval of more energetic fluvial environments and prompted the definition of a new stratigraphic formation in the Mount Sharp group called the Carolyn Shoemaker formation. Glen Torridon hosts abundant phyllosilicates yet remains compositionally and mineralogically comparable to the rest of the Mount Sharp group. Glen Torridon samples have a great diversity and abundance of sulfur-bearing organic molecules, which are consistent with the presence of ancient refractory organic matter. The Glen Torridon region experienced heterogeneous diagenesis, with the most striking alteration occurring just below the Siccar Point unconformity at the Greenheugh pediment. Results from the pediment campaign show that the capping sandstone formed within the Stimson Hesperian aeolian sand sea that experienced seasonal variations in wind direction.

JGR Planets↗

USGS2022

Mars Science Laboratory CheMin data from the Glen Torridon region and the significance of lake-groundwater interactions in interpreting mineralogy and sedimentary history

The Glen Torridon (GT) region is positioned in terrains with strong clay mineral signatures, as inferred from orbital spectroscopy. The GT campaign confirmed orbital distinctions with in situ measurements by the Mars Science Laboratory rover, Curiosity , and the CheMin X-ray diffraction instrument with of some of the highest clay mineral abundances to date. Additionally, GT is unique because of distinct phase identifications for the first time by CheMin, including: (i) Fe-carbonates, and (ii) a novel peak in the XRD patterns of some GT samples, with an interplanar spacing of at 9.2 Å. Fe-carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of multiple samples with Fe-carbonate. This new phase has never been observed in Gale crater with the CheMin instrument and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account the mineralogical, geochemical, and sedimentological constraints in the GT region. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite-minnesotaite (G-M), as a reasonable candidate. The coexistence of Fe-carbonate and Fe-rich clay minerals in the GT samples, supports a conceptual model of a lacustrine groundwater mixing environment in the ancient Gale crater lake. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone controlled the secondary minerals preserved in the Jura, Knockfarril Hill, and Glasgow members of the Mt. Sharp group exposed in GT.

Journal of Geophysical Research E: Planets↗

USGS2022

Evidence for fluctuating wind in shaping an ancient Martian dune field: The Stimson formation at the Greenheugh pediment, Gale crater

Temporal fluctuations of wind strength and direction can influence aeolian bedform morphology and orientation, which can be encoded into the architecture of aeolian deposits. These strata represent a direct record of atmospheric processes and can be used to understand ancient Martian atmospheric processes as well as those on Earth. The strata can: give insight to ancient atmospheric circulation, how the atmosphere evolved in response to global changes in habitability, and how ancient processes differ from modern processes. The Stimson formation at the Greenheugh pediment (Gale crater) records evidence of fluctuating wind across multiple temporal scales. The strata can be subdivided into three intervals–Gleann Beag, Ladder, and Edinburgh intervals. Internally, the intervals record changes of dune morphology and orientation, correlatable to wind fluctuations at multiple temporal scales. The basal Gleann Beag interval comprises compound cross-strata, deposited by oblique compound dunes. These dunes record a bimodal wind regime, resulting in net sediment transport toward the north. The Ladder interval records a reversal of sediment transport to the south, where straight-crested simple-dunes shaped by a seasonally variable winds formed. Finally, the Edinburgh interval records sediment transport to the west, where a unimodal wind formed sinuous-crested simple dunes. These observations demonstrate active and variable atmospheric circulation in Gale crater during the accumulation of the Stimson dune field, at multiple temporal scales from seasonally driven winds to much longer time-frames, during the Hesperian. These observations can be used to further understand ancient atmospheric conditions and processes, at a high temporal resolution on Mars.

Journal of Geophysical Research - Planets↗

USGS2022

Geology and stratigraphic correlation of the Murray and Carolyn Shoemaker formations across the Glen Torridon region, Gale crater, Mars

The Glen Torridon (GT) region within Gale crater, Mars, occurs in contact with the southern side of Vera Rubin ridge (VRR), a well-defined geomorphic feature that is comparatively resistant to erosion. Prior to detailed ground-based investigation of GT, its geologic relationship with VRR was unknown. Distinct lithologic subunits within the Jura member (Murray formation), which forms the upper part of VRR, made it possible to be also identified within GT. This indicates that the strata pass across the geomorphic divide between regions. Furthermore, the cross-bedded lower part of the overlying Knockfarril Hill member (Carolyn Shoemaker formation) also occurs within both VRR and GT. Correlation of both units demonstrates that the strata form a continuous stratigraphic succession regardless of large-scale geomorphic expression. The lithologic change from mudstone (Jura member) to cross-bedded sandstone (Knockfarril Hill member) heralds a significant shift in paleoenvironment from lacustrine to fluvial. The upper part of the Knockfarril Hill member consists of interbedded mudstone and sandstone that transitions to the overlying finely laminated mudstone of the Glasgow member, and a return to lacustrine deposition. In GT, the Stimson formation unconformably overlies the Glasgow member, where it demarks the southern boundary of GT. Contacts for each stratigraphic unit were defined and transferred to a high-resolution image base to make a geologic map and cross sections perpendicular to the NE strike. Stratal dips cannot exceed 2° NW to retain the positions of stratigraphic units in the locations they are exposed throughout GT.

Journal of Geophysical Research: Planets↗

USGS2022

Sedimentological and geochemical perspectives on a marginal lake environment recorded in the Hartmann’s Valley and Karasburg members of the Murray formation, Gale crater, Mars

This study utilizes instruments from the Curiosity rover payload to develop an integrated paleoenvironmental and compositional reconstruction for the 65-m thick interval of stratigraphy comprising the Hartmann's Valley and Karasburg members of the Murray formation, Gale crater, Mars. The stratigraphy consists of cross-stratified sandstone (Facies 1), planar-laminated sandstone (Facies 2), and planar-laminated mudstone (Facies 3). Facies 1 is composed of sandstone showing truncated sets of concave-curvilinear laminae stacked into cosets. Sets are estimated to be meter-to sub-meter-scale, consistent with low-height dunes. Thin stratigraphic intervals of Facies 1 and stacking patterns with Facies 2 and 3 support a wet aeolian dune interpretation. Meter-thick packages of planar-laminated sandstone (Facies 2) are interpreted to represent interfingering dune-interdune strata. Facies 3 consists of meter-thick packages of planar-laminated mudstone interpreted to represent lacustrine deposition with persistent standing water. Integration of geochemistry with each facies reveals some compositional control based on the depositional process. Models for source rock composition from Alpha Particle X-Ray Spectrometer measurements show that facies derived from a basaltic source. Alteration indices and geochemical trends provide evidence that moderate chemical weathering occurred before compositional changes due to diagenesis. Differences in wt% FeO (T) and TiO 2 between facies are minimal, though trends point to sediment sorting in transport. Comparisons to terrestrial basaltic sedimentary systems indicate that the Hartmann's Valley and Karasburg facies reflect deposition in an environment where diverse subaqueous and subaerial facies persisted adjacent to a long-lived body of water.

Journal of Geophysical Research Planets↗

USGS2022

Orbital and in-situ investigation of periodic bedrock ridges in Glen Torridon, Gale Crater, Mars

Wind has been the dominant agent of landscape modification on Mars for the past ~3 billion years. Among the diversity of features formed by aeolian abrasion on the surface of Mars are periodic bedrock ridges (PBRs), a relatively recently recognized class of erosional bedforms on Mars for which Earth analogues are rare. Gale crater, the field site for NASA’s Mars Science Laboratory Curiosity rover since it landed there in 2012, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of periodic, linear bedrock ridges that occur within the Fe/Mg-smectite clay-bearing Glen Torridon region of Aeolis Mons (informally Mount Sharp). During Curiosity’s exploration of the Glen Torridon region between sols ~2300-3080, the rover drove through this field of ridges, providing the first opportunity for the in situ observation of these enigmatic erosional features. This study characterizes the Glen Torridon ridges using orbiter and rover data to determine their morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, the Glen Torridon ridges are interpreted to be consistent with an origin as wind-eroded periodic bedrock ridges carved during the most recent exhumation of Mount Sharp into the present-day mound. Although there is evidence for multidirectional winds in the Glen Torridon region based on the orientation of modern ripples, megaripples, TARs and other bedrock indicators, the consistent orientation of the Glen Torridon ridges, coupled with morphologic asymmetries within the ridges, support formation and elongation of the Glen Torridon PBRs forms parallel to a net regional northerly wind direction in and around Gale crater.

Journal of Geophysical Research E: Planets↗

USGS2021

A rock record of complex aeolian bedforms in a Hesperian desert landscape: The Stimson formation as exposed in the Murray Buttes, Gale Crater, Mars

Lithified aeolian strata encode information about ancient planetary surface processes and the climate during deposition. Decoding these strata provides insight regarding past sediment transport processes, bedform kinematics, depositional landscape, and the prevailing climate. Deciphering these signatures requires a detailed analysis of sedimentary architecture to reconstruct dune morphology, motion, and the conditions that enabled their formation. Here, we show that a distinct sandstone unit exposed in the foothills of Mount Sharp, Gale crater, Mars, records the preserved expression of compound aeolian bedforms that accumulated in a large dune field. Analysis of Mastcam images of the Stimson formation shows that it consists of cross‐stratified sandstone beds separated by a hierarchy of erosive bounding surfaces formed during dune migration. The presence of two orders of surfaces with distinct geometrical relations reveals that the Stimson‐era landscape consisted of large dunes (draas) with smaller, superimposed dunes migrating across their lee slopes. Analysis of cross‐lamination and subset bounding surface geometries indicate a complex wind regime that transported sediment toward the north, constructing oblique dunes. This dune field was a direct product of the regional climate and the surface processes active in Gale crater during the fraction of the Hesperian Period recorded by the Stimson formation. The environment was arid, supporting a large aeolian dune field; this setting contrasts with earlier humid depositional episodes, recorded by the lacustrine sediments of the Murray formation (also Hesperian). Such fine‐scale reconstruction of landscapes on the ancient surface of Mars is important to understanding the planet’s past climate and habitability.

Journal of Geophysical Research - Planets↗

USGS2021

Brine-driven destruction of clay minerals in Gale crater, Mars

Mars’ sedimentary rock record preserves information on geological (and potential astrobiological) processes that occurred on the planet billions of years ago. The Curiosity rover is exploring the lower reaches of Mount Sharp, in Gale crater on Mars. A traverse from Vera Rubin ridge to Glen Torridon has allowed Curiosity to examine a lateral transect of rock strata laid down in a martian lake ~3.5 billion years ago. We report spatial differences in the mineralogy of time-equivalent sedimentary rocks <400 meters apart. These differences indicate localized infiltration of silica-poor brines, generated during deposition of overlying magnesium sulfate–bearing strata. We propose that destabilization of silicate minerals driven by silica-poor brines (rarely observed on Earth) was widespread on ancient Mars, because sulfate deposits are globally distributed.

Science↗

USGS2020

Evidence for a diagenetic origin of Vera Rubin Ridge, Gale Crater, Mars: Summary and synthesis of Curiosity's exploration campaign

This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge (VRR) and summarizes the science results. VRR is a distinct geomorphic feature on lower Aeolis Mons (informally known as Mount Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray‐colored patches concentrated toward the upper elevations of VRR, and these gray patches also contain small, dark Fe‐rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric‐related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record.

Journal of Geophysical Research: Planets↗

USGS2020

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.

Geosphere↗

USGS2020

The chemostratigraphy of the Murray formation and role of diagenesis at Vera Rubin ridge in Gale crater, Mars, as observed by the ChemCam instrument

Geochemical results are presented from Curiosity’s exploration of the Vera Rubin ridge (VRR), in addition to the full chemostratigraphy of the predominantly lacustrine mudstone Murray formation up to and including VRR. VRR is a prominent ridge flanking Aeolis Mons (informally Mt. Sharp), the central mound in Gale crater, Mars, and was a key area of interest for the Mars Science Laboratory mission. ChemCam data show that VRR is overall geochemically similar to lower-lying members of the Murray formation, even though the top of VRR is characterized by strong hematite spectral signatures as observed from orbit. While overall geochemically similar, VRR is characterized by a prominent decrease in Li abundance and Chemical Index of Alteration across the ridge. This decrease follows the morphology of the ridge rather than elevation and is inferred to reflect a non-depositionally controlled decrease in clay mineral abundance in VRR rocks. Additionally, a notable enrichment in Mn above baseline levels is observed on VRR. While not supporting a single model, the results suggest that VRR rocks were likely affected by multiple episodes of post-depositional groundwater interactions that made them more erosionally resistant than surrounding Murray rocks – thus resulting in the modern-day ridge after subsequent erosion.

Journal of Geophysical Research: Planets↗

USGS2020

A lacustrine paleoenvironment recorded at Vera Rubin ridge, Gale crater: Overview of the sedimentology and stratigraphy observed by the Mars Science Laboratory Curiosity rover

For ~500 Martian solar days (sols), the Mars Science Laboratory team explored Vera Rubin ridge (VRR), a topographic feature on the northwest slope of Aeolis Mons. Here we review the sedimentary facies and stratigraphy observed during sols 1,800–2,300, covering more than 100 m of stratigraphic thickness. Curiosity's traverse includes two transects across the ridge, which enables investigation of lateral variability over a distance of ~300 m. Three informally named stratigraphic members of the Murray formation are described: Blunts Point, Pettegrove Point, and Jura, with the latter two exposed on VRR. The Blunts Point member, exposed just below the ridge, is characterized by a recessive, fine-grained facies that exhibits extensive planar lamination and is crosscut by abundant curvi-planar veins. The Pettegrove Point member is more resistant, fine-grained, thinly planar laminated, and contains a higher abundance of diagenetic concretions. Conformable above the Pettegrove Point member is the Jura member, which is also fine-grained and parallel stratified, but is marked by a distinct step in topography, which coincides with localized meter-scale inclined strata, a thinly and thickly laminated facies, and occasional crystal molds. All members record low-energy lacustrine deposition, consistent with prior observations of the Murray formation. Uncommon outcrops of low-angle stratification suggest possible subaqueous currents, and steeply inclined beds may be the result of slumping. Collectively, the rocks exposed at VRR provide additional evidence for a long-lived lacustrine environment (in excess of 10 6 years via comparison to terrestrial records of sedimentation), which extends our understanding of the duration of habitable conditions in Gale crater.

Journal of Geophysical Research: Planets↗