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 "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10^3 to 10^7 Earth years

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10^3 to 10^7 Earth years

Diagenesis Revealed by Fine‐Scale Features at Vera Rubin Ridge, Gale Crater, Mars

International audienceFine scale (submillimeter to centimeter) depositional and diagenetic features encountered during the Curiosity rover's traverse in Gale crater provide a means to understand the geologic history of Vera Rubin ridge (VRR). VRR is a topographically high feature on the lower north slope of Aeolis Mons, a 5 km high stratified mound within Gale crater. We use high spatial resolution images from the Mars Hand Lens Imager (MAHLI) as well as grain sizes estimated with the Gini index mean score technique that uses ChemCam Laser Induced Breakdown Spectroscopy (LIBS) chemical data to constrain the postdepositional history of the strata exposed on this ridge. MAHLI images were used to examine the color, grain size, and style of lamination of the host rocks, as well as to explore the occurrence of nodules, diagenetic crystals, pits, and a variety of dark gray iron rich features. This survey revealed abundant and widespread diagenetic features within the rocks exposed on VRR and demonstrated that rock targets estimated to be coarser generally contain more diagenetic features than those estimated to have finer grains, which indicate that grain size may have influenced the degree and type of diagenesis. A subset of rocks within VRR are gray in color and exhibit the highest proportion of diagenetic features. We suggest that these targets experienced a different diagenetic history than the other rocks on VRR and hypothesize that redistribution and recrystallization of iron within specific intervals may have resulted in both the gray color and the abundance of dark gray iron rich diagenetic features

Diagenesis Revealed by Fine Scale Features at Vera Rubin Ridge, Gale Crater, Mars

International audienceFine scale (submillimeter to centimeter) depositional and diagenetic features encountered during the Curiosity rover's traverse in Gale crater provide a means to understand the geologic history of Vera Rubin ridge (VRR). VRR is a topographically high feature on the lower north slope of Aeolis Mons, a 5 km high stratified mound within Gale crater. We use high spatial resolution images from the Mars Hand Lens Imager (MAHLI) as well as grain sizes estimated with the Gini index mean score technique that uses ChemCam Laser Induced Breakdown Spectroscopy (LIBS) chemical data to constrain the postdepositional history of the strata exposed on this ridge. MAHLI images were used to examine the color, grain size, and style of lamination of the host rocks, as well as to explore the occurrence of nodules, diagenetic crystals, pits, and a variety of dark gray iron rich features. This survey revealed abundant and widespread diagenetic features within the rocks exposed on VRR and demonstrated that rock targets estimated to be coarser generally contain more diagenetic features than those estimated to have finer grains, which indicate that grain size may have influenced the degree and type of diagenesis. A subset of rocks within VRR are gray in color and exhibit the highest proportion of diagenetic features. We suggest that these targets experienced a different diagenetic history than the other rocks on VRR and hypothesize that redistribution and recrystallization of iron within specific intervals may have resulted in both the gray color and the abundance of dark gray iron rich diagenetic features

Extraformational sediment recycling on Mars

International audienc

'HIGH' BUT NOT SO DRY ON AEOLIS MONS:: TRANSIENT LAKE SYSTEMS IN HESPERIAN DESERTS IN GALE CRATER

International audienceThe stratigraphy preserved within Aeolis Mons in Gale crater (Mars) shows a major transition from a phyllosilicate-bearing unit, which in situ data show is composed of mudstone-rich strata (with subordinate sandstones) recording deposition in lacustrine to fluvial settings into a major sulfatebearingunit that is hundreds of meters thick (the Layered Sulfate-bearing unit (LSu)) [1,2,3,4]. The origin of the LSu unit is not yet constrained.Comparison to other terrains on Mars has led to the hypothesis that the transition from clay minerals to sulfates records a planet-wide change in climate from relatively warm and wet to cold and arid [1]. A leading question is whether this transition is so unidirectional. The lower section of the LSu (claysulphate transition stratigraphy) contains strongy diagenetically altered strata or stacked, cross-bedded facies (Dunnideer and Port Logan mbs of the Mirador fm) that likely records a purely dry aeolian dune environment [5]. However, higher up in the studied section within the Contigo member, we observe sandstone lenses interstratified within aeolian strata that show distinctive sedimentary structures indicative of deposition by lacustrine and fluvial processes in shallow interdune depressions [6]. In late 2022, Curiosity investigated a distinctive dark-toned, resistant unit even higher within the sulfate-bearing stratigraphy of Aeolis Mons – the “Marker Band” [1,4,7,8]. Stratigraphically it has been informally designated the Amapari member of the Mirador formation (Mt. Sharp gp). This unit can be traced for tens of kilometers around Aeolis Mons [7], and from early in the mission was considered an important geologic target for investigation [1]. The key question concerning the “Marker Band” is what geological process led to its formation and how does it relate to the Layered Sulfate-bearing unit. Orbital-scale observations led to favored interpretations of the “Marker Band” as a volcanic ash deposit or a more indurated sulfate unit [7]. The first edge-on view in the distance favored an eolian deflation surface [3]. Here we describe the sedimentology of unit and go on to discuss initial implications for paleoenvironmental and paleoclimatic interpretations

'HIGH' BUT NOT SO DRY ON AEOLIS MONS:: TRANSIENT LAKE SYSTEMS IN HESPERIAN DESERTS IN GALE CRATER

International audienceThe stratigraphy preserved within Aeolis Mons in Gale crater (Mars) shows a major transition from a phyllosilicate-bearing unit, which in situ data show is composed of mudstone-rich strata (with subordinate sandstones) recording deposition in lacustrine to fluvial settings into a major sulfatebearingunit that is hundreds of meters thick (the Layered Sulfate-bearing unit (LSu)) [1,2,3,4]. The origin of the LSu unit is not yet constrained.Comparison to other terrains on Mars has led to the hypothesis that the transition from clay minerals to sulfates records a planet-wide change in climate from relatively warm and wet to cold and arid [1]. A leading question is whether this transition is so unidirectional. The lower section of the LSu (claysulphate transition stratigraphy) contains strongy diagenetically altered strata or stacked, cross-bedded facies (Dunnideer and Port Logan mbs of the Mirador fm) that likely records a purely dry aeolian dune environment [5]. However, higher up in the studied section within the Contigo member, we observe sandstone lenses interstratified within aeolian strata that show distinctive sedimentary structures indicative of deposition by lacustrine and fluvial processes in shallow interdune depressions [6]. In late 2022, Curiosity investigated a distinctive dark-toned, resistant unit even higher within the sulfate-bearing stratigraphy of Aeolis Mons – the “Marker Band” [1,4,7,8]. Stratigraphically it has been informally designated the Amapari member of the Mirador formation (Mt. Sharp gp). This unit can be traced for tens of kilometers around Aeolis Mons [7], and from early in the mission was considered an important geologic target for investigation [1]. The key question concerning the “Marker Band” is what geological process led to its formation and how does it relate to the Layered Sulfate-bearing unit. Orbital-scale observations led to favored interpretations of the “Marker Band” as a volcanic ash deposit or a more indurated sulfate unit [7]. The first edge-on view in the distance favored an eolian deflation surface [3]. Here we describe the sedimentology of unit and go on to discuss initial implications for paleoenvironmental and paleoclimatic interpretations