Characterizing the Stratigraphy of the Nili Planum Region Outside Jezero Crater: Implications for Mars 2020 Strategic Planning (original) (raw)
Sequence stratigraphy in extraterrestrial settings: The Jezero crater, Mars
Marine and Petroleum Geology, 2023
The analysis of high-resolution images provided by the Perseverance rover indicates the presence of a Gilbert type deltaic complex in the western part of the Jezero crater, which includes fluvial topsets, as well as subaqueous clinoforms. While previously considered to be genetically related, the topsets and the foresets are separated by subaerial unconformities and belong to different sedimentation cycles (depositional sequences) and systems tracts. Based on the stratal stacking patterns observed at Kodiak butte, the clinoforms belong to fallingstage systems tracts, as indicated by the downstepping trajectory of the clinoform rollovers, the occasional preservation of offlap, and the sharp-based nature of the clinoforms. In contrast, the topsets are part of the lowstand systems tracts of the overlying depositional sequences, and are separated from the underlying foresets by truncation surfaces (i.e., subaerial unconformities). The possible environments for the deposition of clinoforms in the Jezero crater range from lacustrine to marine. In the latter case, a connection between the Jezero Basin and a northern ocean can be inferred, allowing for the possibility of tidal processes influencing the patterns of deposition within the deltaic complex. This may explain the rhythmites observed in the deltaic foresets, although other explanations for the cyclic changes in lithology and energy conditions, such as seasonal variations in fluvial discharge and sediment load, are also possible. The location of the Jezero crater in the shoreline area of the Isidis Basin, which is a bay of the northern ocean, may have created a configuration of interconnected embayments able to amplify the otherwise small tidal range expected from the two moons of the planet. Clarification of the paleogeography at the time of deltaic progradation (c. 3.6-3.8 Ga) has major implications for the strategy of exploration for early life forms on Mars. The acquisition of rock samples from the Jezero Basin and the northern ocean are essential to gain further insight into the early land-ocean interaction and possible co-evolution of life and environments on Mars.
Journal of Geophysical Research: Planets
We report the results of geological studies by the Opportunity Mars rover on the Endeavour Crater rim. Four major units occur in the region (oldest to youngest): the Matijevic, Shoemaker, Grasberg, and Burns formations. The Matijevic formation, consisting of fine-grained clastic sediments, is the only pre-Endeavour-impact unit and might be part of the Noachian etched units of Meridiani Planum. The Shoemaker formation is a heterogeneous polymict impact breccia; its lowermost member incorporates material eroded from the underlying Matijevic formation. The Shoemaker formation is a close analog to the Bunte Breccia of the Ries Crater, although the average clast sizes are substantially larger in the latter. The Grasberg formation is a thin, fine-grained, homogeneous sediment unconformably overlying the Shoemaker formation and likely formed as an airfall deposit of unknown areal extent. The Burns formation sandstone overlies the Grasberg, but compositions of the two units are distinct; there is no evidence that the Grasberg formation is a fine-grained subfacies of the Burns formation. The rocks along the Endeavour Crater rim were affected by at least four episodes of alteration in the Noachian and Early Hesperian: (i) vein formation and alteration of preimpact Matijevic formation rocks, (ii) low-water/rock alteration along the disconformity between the Matijevic and Shoemaker formations, (iii) alteration of the Shoemaker formation along fracture zones, and (iv) differential mobilization of Fe and Mn, and CaSO 4 -vein formation in the Grasberg and Shoemaker formations. Episodes (ii) and (iii) possibly occurred together, but (i) and (iv) are distinct from either of these.
Geomorphology of Ma'adim Vallis, Mars, and associated paleolake basins
Journal of Geophysical Research, 2004
1] Ma'adim Vallis, one of the largest valleys in the Martian highlands, appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads. Ma'adim Vallis debouched to Gusev crater, 900 km to the north, the landing site for the Spirit Mars Exploration Rover. Support for the paleolake overflow hypothesis comes from the following characteristics: (1) With a channel width of 3 km at its head, Ma'adim Vallis originates at two (eastern and western) gaps incised into the divide of the $1.1 M km 2 enclosed Eridania head basin, which suggests a lake as the water source.
Icarus, 2021
Impact craters on Mars preserve diverse records of volcanic, fluvial, and glacial activities. Enigmatically, the preservation of these major activities or records altogether within impact craters is rare. We report one such new observation of impact craters that formed on a volcanic dome studied using data from the Mars Reconnaissance Orbiter's (MRO) Context Camera (CTX), High-Resolution Imaging Science Experiment (HiRISE), and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA), and Mars Express' High-Resolution Stereo Camera (HRSC). A ~20 km diameter impact crater, informally named as Degana-A, is formed within the ~50 km diameter impact crater Degana. Mineralogical analysis reveals exposures of low-calcium pyroxene and olivine deposits, which occupy Degana-A's eastern walls, leading to the idea that pristine Noachian bedrocks might be exposed from beneath the volcanic dome. Degana-A floor is completely covered by alluvial fans from all sides with distributaries. Within Degana crater, multiple fans are observed along its eastern to southern side only. The most likely source of water was the accumulation of snow on Degana crater walls, which possibly melted as a result of the impact of Degana-A. We observed a ~1 km wide breach on the eastern wall of Degana-A and the estimated maximum flow velocity is ~2 m/s and a runoff ~2.25 mm/hr. Over the south-facing walls, multiple moraine-like ridges superposed the fans, which suggests overprinting by glacial activities. The presence of fans and superposed moraine-like ridges located at the mid-latitudes (~23°S) implies atmosphere-derived snow/ice precipitation was possible. Chronologically, the dome is of Noachian age, whereas Degana crater formed in the Hesperian period and crater retention on the fans indicates late Hesperian to Amazonian ages. Overall, the preserved Noachian crustal material underneath a volcanic dome is rarely exposed in its pristine context, which offers a rare window into early igneous processes. This intriguing location also witnessed a climatic transition as implied by water/ice derived landforms formed by non-coeval events. 100 glacial landforms. Likewise, no mineralogical analysis has been carried out over this volcanic 101 dome to decipher the Noachian mineralogy. Thus, this region offers a unique chance to observe 102 volcanic, impact, glacial, and fluvial landforms in the same location, assessing whether the 103 processes that formed them occurred in concert or not. In addition, the composition of such 104 Noachian volcanoes is critical to understand the evolution of ancient volcanic crust on Mars (Xiao
Post-Viking View of Martian Geologic Evolution
1980
The mean density, 3.933 g/cm 3, and the estimated moment of inertia factor, 0.365, constrain the density distribution within Mars but do not define it uniquely. For plausible core densities, core radii can range from-•1350 to-•2200 km, with the core constituting from-•13 to-•35% of the planet's mass. Possible extremes for the zero-pressure density of the Martian mantle could be as high as-•3.6 g/cm 3 or as low as-•3.3 g/cm 3. The Martian mantle is probably denser than the terrestrial mantle; however, the actual density and composition of the Martian mantle are not well constrained by present data. The dominant Martian lavas are probably marie or ultramarie. Viking lander analyses suggest that soils are hydrated, Fe 3+bearing weathering products of marie rocks. Earth-based reflectance spectra indicate olivine (or basaltic glass) and pyroxene in dark areas and several percent Fe 3+ oxides in bright areas; integral disk spectra indicate the presence of H20 ice and mineral hydrates. Stable weathering products under current surface conditions are primarily oxides and carbonates. Martian surface materials probably consist of variable proportions of made igneous minerals and weathering products; the actual mineralogy is not well constrained by present data. A major geologic dichotomy exists between the complex northern plains and the ancient southern cratered terrain. The Thatsis plateau, which dominates the low-degree harmonics of the gravity field, appears to be only partially compensated; Olympus Mons appears to be completely uncompensated. Substantial stresses must be supported, either statically by a thick, rigid lithosphere, or dynamically. Mean crustal thicknesses ranging from 23 to 40 km have been obtained from modeling of Bouguer gravity data. Lithospheric thicknesses ranging from 25 to 50 km under volcanoes in the Thatsis and Elysium provinces to > 150 km under Olympus Mons have been obtained from consideration of the effects of mass loading by volcanic constructs. Many of the compressional and extensional features on Mars have orientations consistent with formation by fracturing in response to loading by the Thatsis plateau. The deficiency of small craters within cratered terrain is attributed to obliteration by volcanism which formed the intercrater plains in cratered terrain. These intercrater plains, which appear to be the first units formed after the ancient cratered terrain, overlap in relative ages with the ridged plains and the fretted regions; remaining plains units are younger. The maximum resurfacing rate due to volcanism occurred between 1.0 and 1.5 b.y. ago if a constant cratering flux is assumed and between 3.5 and 4.0 b.y. ago if the lunar cratering flux (scaled to Mars) is assumed. Thermal evolution models have considered the formation of initial crust, core formation, mantle differentiation, and planetary radius changes, but not the major geologic asymmetries of Mars. The time scales of thermal evolution models can be lengthened or shortened by making various assumptions about initial temperatures and heat sources. Models in which the core formed in the first billion years and in which the peaks of mantle differentiation, volcanism, and planetary radius occur between 1.5 and 3.5 b.y. ago are consistent with a Martian cratering flux intermediate between the constant flux model and the scaled lunar flux. The high •SN/•nN ratio of the Martian atmosphere, 1.7 times the terrestrial value, is ascribed to mass-dependent loss of 10-150 times the present amount of atmospheric •nN. The absence of observable isotopic effects in C and O suggests that atmospheric CO2 and H20 must exchange periodically with a larger, normally nonatmospheric reservoir. The Martian atmosphere exhibits a 'planetary' type pattern of noble gas abundances, with xenon depleted in relation to the other noble gases. Estimates of the whole planet column abundances of CO2 and H20 range from 290 to 8000 g/cm 2 and from 600 to 1600 g/cm 2, respectively. Amounts of H20 and CO2 which are comparable to or perhaps greatly in excess of the whole planet estimates made on the basis of atmospheric noble gas abundances can be stored in plausible reservoirs: the residual polar caps; hydration, oxidation, and carbonation of surface materials; adsorption and absorption into the regolith; and as subsurface ices. A number of surface features have morphologies which appear to require tens of meters of water, and perhaps more, for their formation: fretted terrain, channels, patterned or polygonal ground, rampart ejecta deposits, and possible table mountains.
Martian Cratering 7: The Role of Impact Gardening
Icarus, 2001
Viking-era researchers concluded that impact craters of diameter D < 50 m were absent on Mars, and thus impact gardening was considered negligible in establishing decameter-scale surface properties. This paper documents martian crater populations down to diameter D ∼ 11 m and probably less on Mars, requiring a certain degree of impact gardening. Applying lunar data, we calculate cumulative gardening depth as a function of total cratering. Stratigraphic units exposed since Noachian times would have experienced tens to hundreds of meters of gardening. Early Amazonian/late Hesperian sites, such as the first three landing sites, experienced cumulative gardening on the order of 3-14 m, a conclusion that may conflict with some landing site interpretations. Martian surfaces with less than a percent or so of lunar mare crater densities have negligible impact gardening because of a probable cutoff of hypervelocity impact cratering below D ∼ 1 m, due to Mars' atmosphere. Unlike lunar regolith, martian regolith has been affected, and fines removed, by many processes. Deflation may have been a factor in leaving widespread boulder fields and associated dune fields, observed by the first three landers. Ancient regolith provided a porous medium for water storage, subsurface transport, and massive permafrost formation. Older regolith was probably cemented by evaporites and permafrost, may contain interbedded sediments and lavas, and may have been brecciated by later impacts. Growing evidence suggests recent water mobility, and the existence of duricrust at Viking and Pathfinder sites demonstrates the cementing process. These results affect lander/rover searches for intact ancient deposits. The upper tens of meters of exposed Noachian units cannot survive today in a pristine state. Intact Noachian deposits might best be found in cliffside strata, or in recently exhumed regions. The hematite-rich areas found in Terra Meridiani by the Mars Global Surveyor are probably examples of the latter.
Analysis of crater valleys, Noachis Terra, Mars: Evidence of fluvial and glacial processes
The precise mechanism for the formation and evolution of crater valley networks in the Martian southern highlands remains under debate, with precipitation, groundwater flow, and melting induced by impact being suggested. We studied valley networks within four craters of the Noachis Terra highlands that were representative of similar features in Noachis Terra and where orbital data existed for analysis in order to characterise their morphology and infer possible processes involved in their formation and evolution. We found evidence for valleys carved by liquid water and ice-related processes. This included strong evidence of liquid water-based valley formation through melting of ice-rich deposits throughout our study area, suggesting an alternative to previously suggested rainfall or groundwater-based scenarios. The location of these valleys on steeply sloping crater walls, as opposed to the shallow slopes of the highlands where Martian valleys are typically found, suggested that our 'fluvial' valleys had not evolved a more structured fluvial morphology as valley networks found on the Martian plains. Our studied valleys' association with ice-rich material and abundant evidence for erosion caused by downslope flow of ice-rich material are consistent with a cold, wet Mars hypothesis where accumulation, flow, and melting of ice have been dominant factors in eroding crater valleys. Additionally, analysis of valley morphology with slope and aspect suggested a greater dependence on local geology and presence of volatiles than larger valley networks, though ice-related valleys were consistently wider for their length than valleys assessed as fluvial carved. We assessed that local conditions such as climate, geology, and availability of ice-rich material played a major role in the erosion of crater valleys at our study site.
Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars
Science
The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater’s sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide–rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks have been stored aboard Perseverance for potential return to Earth.
Geomorphic Evolution of the Martian Highlands Through Ancient Fluvial Processes
Journal of Geophysical Research, 1993
Craters in the Martian highlands are preserved in various stages of degradation. As a result of an erosional process active from the Middle Noachian (4.40-3.92 b.y.) through the Hesperian (3.55-1.8 b.y.), ejecta associated with fresh impact craters became etched, hummocky, and dissected by rimoff channels. With time, interior gullies became deeply incised and ejecta deposits were entirely removed. Infilling of the craters followed until, in some instances, the craters were completely buried. Only fluvial processes explain these morphologic variations, the size range of affected craters, and the size-frequency distribution curves associated with these crater populations. Based on the number of superposed fresh impact craters, fluvial processes affecting the highlands ceased entirely by the end of the Hesperian. No correlation between cessation of degradation and latitude exists. However, a strong correlation exists between cessation of degradation and elevation. Degradation ended at higher elevations (e.g., 3-4 km; N[5]=~200, Late Noachian) before lower elevations (e.g., 1-2 km; N[5]=~180, Early Hesperian), suggesting that cessation was coupled to desiccation of the volatile reservoir and degassing of a 5-20 bar primordial atmosphere. Volatiles released to the surface by rimoff channel formation and seepage may have been part of a complex hydrologic cycle that included periodic, heavy amounts of precipitation. Rainfall was principally responsible for degrading the highlands, eroding impact craters, and redistributing sediments. Rainfall also recharged the highland aquifers, allowing sapping and seepage to continue for hundreds of millions of years. As the primordial atmosphere was lost, cloud condensation, and thus rainfall and aquifer recharge, occurred at progressively lower elevations. Based on estimates on the amount of material removed and duration of degradation, denudation rates averaged 0.0001-0.005 mm/yr. These rates are equivalent to those in ten'estrial periglacial environments. [Soderblom et al., 1973; Mutch et al., 1977, pp. 138-150]. The comprehensive analysis of the cratered highlands presented here suggests that during the Noachian (4.6 to ~3.5 Ga), surface processes and denudation rates on Mars were similar to those presently occurring in periglacial environments on Earth. Cessation of these processes appears to have been coupled to desiccation of the volatile reservoir and degassing of the early planetary atmosphere. 3453 3454 CRADDOCK AND MAXWF_,LL: ANCIENT FLUVI• PROCESSES ON MARS ß o o • Fig. 1. Shaded relief map of the equatorial region of Mars. Areas outlined show the location of the Npl• and Npld materials between 30 ø and-30 ø latitude investigated in this study. Base maps are the 1:15,000,000 Shaded Relief Map of Mars, Eastern and Western Regions [U.S. Geological Survey, 1985]. MORPHOLOGY OF HIG• IMPACT CRATERS A number of investigations have dealt with the general degrade d appearance of craters in the Martian highlands. Based on Mariner spacecraft data, McGill and Wise [1972] and Arvidson [1974] indicated that fresh, bowl-shaped craters grade into flatfloored, rimless craters. Using high-resolution Viking orbiter data, Grant and Schultz [1991a, b] compared styles of crater degradation in southern Ismenius Lacus to the evolution of terrestrial impact craters. These studies are important for determining how highland impact craters became degraded and for identifying the processes that operated to modify them. However, the Mariner-based studies presented broad crater classes without distinguishing smaller, significant features that are visible in Viking orbiter images. Also, highland studies north of 30 ø latitude are biased towards identifying the degradational process as aeolian in nature due to the presence of large airfall (i.e., dust) deposits in the region [Christensen, 1982, 1986; Greeley and Guest, 1987; Schultz and Lutz, 1988; Grizzaffi and Schultz, 1989; Dimitriou, 1990a, b; Grant and Schultz, 1990; Moore, 1990] which were emplaced subsequent to highland degradation and crater modification [Dimitriou, 199Os, b]. Highland crater populations in the equatorial region of Mars show styles of degradation that are consistent with fluvial processes. Fresh impact craters typically have sharply defined raised rims, hummocky floors, and obvious ejecta deposits (Figure 2a). Martian gravity causes some small-scale collapse of the rim to occur on craters with diameters greater than ~5 km, producing a fresh impact crater with a complex morphology [Pike and Davis, 1984; Pike, 1988]. The ejects associated with fresh Martian impact craters either radiates out from the center of impact (similar to most hmar craters), is lobate from the center and is said to be "fluidized" [Mouginis-Mark, 1979], or falls somewhere in between these two types. Fluidized ejects may represent the presence of subsurface volatiles [Carr et al., 1977] or may be the result of atmospheric deceleration of ejected particles [Schultz and Gault, 1979]. Geographic variations in the occurrence of these types of fresh impactscraters have been the subject of numerous CRADDOCK AND MAXWELL: ANCIENT FLUVIAL PROCESSES ON MARS 3455
Context of ancient aqueous environments on Mars from in situ geologic mapping at Endeavour Crater
Journal of Geophysical Research: Planets, 2015
Using the Mars Exploration Rover Opportunity, we have compiled one of the first field geologic maps on Mars while traversing the Noachian terrain along the rim of the 22 km diameter Endeavour Crater (Latitude À2°16′33″, Longitude À5°10′51″). In situ mapping of the petrographic, elemental, structural, and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units. Three of these rock units predate the surrounding Burns formation sulfate-rich sandstones and one, the Matijevic Formation, represents conditions on early Mars predating the formation of Endeavour Crater. The stratigraphy assembled from these observations includes several geologic unconformities. The differences in lithologic units across these unconformities record changes in the character and intensity of the Martian aqueous environment over geologic time. Water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls. These oldest pre-Endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed. The alteration along joints in the oldest rocks and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and/or hydrothermal fluids circulated through the early Martian crust. The wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large (>8 km in diameter) impact craters is complex. These results imply that geologic complexity is to be anticipated in other areas of Mars where cratering has been a fundamental process in the local and regional geology and mineralogy.
Astrobiology, 2020
Jezero crater has been selected as the landing site for the Mars 2020 Perseverance rover, because it contains a paleolake with two fan-deltas, inlet and outlet valleys. Using the data from the High Resolution Stereo Camera (HRSC) and the High Resolution Imaging Science Experiment (HiRISE), we conducted a quantitative geomorphological study of the inlet valleys of the Jezero paleolake. Results show that the strongest erosion is related to a network of deep valleys that cut into the highland bedrock well upstream of the Jezero crater and likely formed before the formation of the regional olivine-rich unit. In contrast, the lower sections of valleys display poor bedrock erosion and a lack of tributaries but are characterized by the presence of pristine landforms interpreted as fluvial bars from preserved channels, the discharge rates of which have been estimated at 10 3-10 4 m 3 s-1. The valleys' lower sections postdate the olivine-rich unit, are linked directly to the fan-deltas, and are thus formed in an energetic, late stage of activity. Although a Late Noachian age for the fan-deltas' formation is not excluded based on crosscutting relationships and crater counts, this indicates evidence of a Hesperian age with significant implications for exobiology.
In Situ Evidence for an Ancient Aqueous Environment at Meridiani Planum, Mars
Science, 2004
Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.
HAL (Le Centre pour la Communication Scientifique Directe), 2023
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Sustained fluvial deposition recorded in Mars' Noachian stratigraphic record
Nature Communications, 2020
Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6-3.0 Ga. Despite widespread geomorphic evidence, few analyses of Mars' alluvial sedimentary-stratigraphic record exist, with detailed studies of alluvium largely limited to smaller sand-bodies amenable to study in-situ by rovers. These typically metre-scale outcrop dimensions have prevented interpretation of larger scale channel-morphology and long-term basin evolution, vital for understanding the past Martian climate. Here we give an interpretation of a large sedimentary succession at Izola mensa within the NW Hellas Basin rim. The succession comprises channel and barform packages which together demonstrate that river deposition was already well established >3.7 Ga. The deposits mirror terrestrial analogues subject to low-peak discharge variation, implying that river deposition at Izola was subject to sustained, potentially perennial, fluvial flow. Such conditions would require an environment capable of maintaining large volumes of water for extensive time-periods, necessitating a precipitation-driven hydrological cycle.
A chronology of early Mars climatic evolution from impact crater degradation
The degradation of impact craters provides a powerful tool to analyze surface processes in the martian past. Previous studies concluded that large impact craters (20-200km in diameter) were strongly degraded by fluvial erosion during early martian history. Our goal is to study the progression of crater degradation through time with a particular emphasis on the craters with alluvial fans, and on the relative chronology of these craters. The geometric properties of 283 craters of >20km in diameter were analyzed in two highlands of Mars, north of Hellas Planitia, and south of Margaritifer Terra, both known to contain craters with alluvial fans. Three classes were defined from morphology: strongly degraded craters with fluvial landforms and without ejecta (type I), gently degraded craters with fluvial landforms and preserved ejecta (type II), and fresh craters with ejecta and no fluvial landforms (type III). Our main result is that the type II craters that present alluvial fans have characteristics closer to fresh craters (type III) than degraded craters (type I). The distinctive degradation characteristics of these classes allowed us to determine a temporal distribution: Type I craters were formed and degraded between ~4Gy and ~3.7Gy and type II craters with alluvial fans were formed between Early Hesperian and Early Amazonian (~3.7 to ~3.3Gy). This chronology is corroborated by crosscutting relationships of individual type II craters, which postdate Late Noachian valley networks. The sharp transition at ~3.7Gy suggests a quick change in climatic conditions that could correspond to the cessation of the dynamo.
A morphometric and morphologic catalog of~100 small craters imaged by the Opportunity rover over the 33.5 km traverse between Eagle and Endeavour craters on Meridiani Planum shows craters in six stages of degradation that range from fresh and blocky to eroded and shallow depressions ringed by planed off rim blocks. The age of each morphologic class from <50-200 ka to~20 Ma has been determined from the size-frequency distribution of craters in the catalog, the retention age of small craters on Meridiani Planum, and the age of the latest phase of ripple migration. The rate of degradation of the craters has been determined from crater depth, rim height, and ejecta removal over the class age. These rates show a rapid decrease from~1 m/Myr for craters <1 Ma to~<0.1 m/Myr for craters 10-20 Ma, which can be explained by topographic diffusion with modeled diffusivities of~10 À6 m 2 /yr. In contrast to these relatively fast, short-term erosion rates, previously estimated average erosion rates on Mars over~100 Myr and 3 Gyr timescales from the Amazonian and Hesperian are of order <0.01 m/Myr, which is 3-4 orders of magnitude slower than typical terrestrial rates. Erosion rates during the Middle-Late Noachian averaged over~250 Myr, and~700 Myr intervals are around 1 m/Myr, comparable to slow terrestrial erosion rates calculated over similar timescales. This argues for a wet climate before~3 Ga in which liquid water was the erosional agent, followed by a dry environment dominated by slow eolian erosion.
Geological Evolution of the Tyras Vallis Paleolacustrine System, Mars
Journal of Geophysical Research, 2006
1] Using the new High Resolution Stereo Camera (HRSC) data and other Martian data sets, we reconstructed the hydrological history of an unnamed complex crater in the Xanthe Terra region. The crater hosted a lacustrine basin fed by a dense and centripetal drainage system, developed along its inner rim, and by the Tyras Vallis channel. Where the Tyras Vallis opens into the crater, a prominent delta-like feature is visible, characterized by a central terrace and two small longitudinal scarps. This deposit has been used as sedimentary recorder of the crater lake history and allowed assessment of the overall hydrological evolution. Two major stands of the water level have been inferred at 700 and 550 m above the crater floor, based on the correlation between the morphology and topography of the fan and the crater floor deposits. Our reconstruction reveals a complex sedimentary evolution of the fan, which underwent deltaic and alluvial sedimentation, as a result of the different lake water levels and Tyras Vallis supplies. A dominant erosional evolution of the fan-delta was determined by the interaction between the fluvial characteristics and basin wave regime. Wave height analysis and morphological comparison with terrestrial analogues support this hypothesis. The lacustrine activity could be chronologically placed between the Late Noachian and the Hesperian. The climatic conditions could have allowed the recharge of the regional groundwater system by precipitation and episodic fluvial activity. However, also heating effects of cratering could have affected the system, rejuvenating or accelerating the recharge of the local aquifer.
Prime candidate sites for astrobiological exploration through the hydrogeological history of Mars
Planetary and Space Science, 2005
The hydrogeological evolution of Mars has been proposed to be dominated by the development of the Tharsis Magmatic Complex through superplume activity, with related magmatic-pulse-driven flood inundations that directly influence the shaping of the northern plains, the evolution of the atmosphere and climate, and subsurface and surface water processes. On the other hand, several possible biological models and terrestrial analogues have been suggested for Mars during the last decade, including the description of putative microfossils and the proposal of sedimentary units. Here we revisit these scenarios and present a possible bridge that integrates the geological, paleohydrological, and the putative biological histories of the planet. We primarily focus on the Noachian, a time period that arguably has recorded an inner dynamo, plate tectonics, and an ocean that may have covered one-third of the total surface area of Mars, due to its implications on the possible origin and early evolution of life. This stage is followed by a long-lived cold and dry phase, briefly punctuated by transient magmatic-driven hydrological cycles, dominated by a stagnant-lid/ superplume regime, which directly influences the processes of natural selection on the putative early biosphere. Based on this hypothesized evolution of the planet, we suggest three martian locations as prime candidate sites for astrobiological exploration, each one corresponding to an inundation period: Meridiani Planum (Noachian/Early Hesperian), Mangala Valles (Late Hesperian/ Early Amazonian), and Orcus Patera (Amazonian).
… Planets (1991–2012 …, 2010
1] The Ares Vallis region is surrounded by highland terrain containing both degraded and pristine large impact craters that suggest a change in climate during the Late Noachian-Early Hesperian, from warmer, wetter conditions to colder, dryer conditions. However, the regional occurrence of Hesperian-age crater outlet channels indicates that this period on Mars was characterized by episodic climate fluctuations that caused transient warming, facilitating the stability of liquid water at the surface. An extensive survey of the morphology and topography of 75 impact basins in the region indicates that of the largest degraded craters, 4 were identified with single outlet channels that suggest the former presence of water infill. These basins lack inlets indicating that water influx was likely derived from sapping of groundwater. A comparison of measured crater rim heights to modeled rim heights suggests that the bulk of the depth/diameter reduction on these craters was the result of infilling, possibly by sediments. Crater statistics indicate that crater degradation and infill occurred during a short 200 Ma interval in the Late Noachian, from 3.8 Ga to 3.6 Ga. Craters that formed after 3.6 Ga exhibit a near-pristine morphology. Our results support the hypothesis of rapid climate change at the end of the Noachian period. However, geologic relationships between the crater outlet channels and Ares Vallis indicate that drainage occurred only after the period of intense crater modification, during the Hesperian (3.5-2.9 Ga). This suggests a delay between the time of infill of the craters and the time of drainage.