Evidence of Amazonian era ice Ages From Terra Cimmeria, Mars

Amazonian-aged fluvial system and associated ice-related features in Terra Cimmeria, Mars

Authors:

Adeli et al

Abstract:

The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340 km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between View the MathML source∼1.8−0.2+0.2 Ga to View the MathML source510−40+40 Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events.

Was the Noctis Labyrinthus on Mars Produced by Groundwater Flows Collapsing the Ground Above?

Groundwater flow induced collapse and flooding in Noctis Labyrinthus, Mars

Authors:

Rodriguez et al

Abstract:

Catastrophic floods of enormous proportions are thought to have played a major role in the excavation of some of the Solar System’s largest channels; the circum-Chryse outflow channels. The generation of the floods has been attributed to both the evacuation of regional highland aquifers and ancient paleo-lakes. Numerous investigators indicate that these source regions were likely recharged and pressurized by eastward groundwater flow via conduits extending thousands of kilometers from an elevated groundwater table in the Tharsis volcanic rise. This hypothesis remains controversial, largely because subsequent stages of Valles Marineris development and enlargement would have resulted in the widespread destruction of the proposed groundwater paths. Here, we show that Noctis Labyrinthus, a unique canyon system connecting the Tharsis volcanic rise and western Valles Marineris, retains geologic evidence of conduit development associated with structurally-controlled groundwater flow through salt-rich upper crustal deposits, consistent with aquifer drainage from the Tharsis volcanic rise region. Our investigation indicates that subsequent surface collapse over these conduits during the Hesperian Period resulted in the generation of large basins in the central and eastern regions of Noctis Labyrinthus, and contributed to the chasmata formation in the western portion of Valles Marineris. The lava-covered floors of these basins, dated by previous workers as Late Amazonian, contain hydrated mineral deposits occurring in spatial coexistence with decameter-scale features that we interpret to be lacustrine and periglacial in origin. The proposed paleo-lake sites also include chaotic terrains, which could comprise groundwater discharge zones, pointing to regional hydrologic processes that could have operated from the Early Hesperian until a few tens of millions of years ago. Episodic fluidized discharges from eastern Noctis Labyrinthus troughs delivered vast volumes of sediments and volatiles into western Valles Marineris, contributing to the construction of a regional volatile-rich stratigraphy. Episodic groundwater discharges and the resulting intermittent formation of lakes within regional tectono-volcanic basins could have lasted hundreds of millions of years, making the study region of prime interest for astrobiological exploration.

Evidence Clay Formed on Mars Less Than 2 Billion Years ago During the Amazonian

Recent orbital and rover missions to Mars have turned up ample evidence of clays and other hydrated minerals formed when rocks are altered by the presence of water. Most of that alteration is thought to have happened during the earliest part of Martian history, more than 3.7 billion years ago. But a new study shows that later alteration -- within the last 2 billion years or so -- may be more common than many scientists had thought.

The research, by Brown University geologists Ralph Milliken and Vivian Sun, is in press in the Journal of Geophysical Research: Planets.

The lion's share of the clay deposits found on Mars thus far have turned up in terrains that date back to the earliest Martian epoch, known as the Noachian period. Clays also tend to be found in and around large impact craters, where material from deep below the surface has been excavated. Scientists have generally assumed that the clays found at impact sites probably formed in the ancient Noachian, became buried over time, and then were brought back to the surface by the impact.

That assumption is particularly true of clay deposits found in crater central peaks. Central peaks are formed when, in the aftermath of an impact, rocks from within the crust rebound upward, bringing layers to the surface that had been buried many kilometers deep.

"Because central peaks contain rocks uplifted from depth, some previous studies have assumed the clays found within central peak regions are uplifted too," said Milliken, assistant professor of Earth, environmental and planetary sciences. "What we wanted to do was look at lots of these craters in detail to see if that's actually correct."

Milliken and Sun performed a survey of 633 crater central peaks distributed across the Martian surface. They looked at detailed mineralogy data collected by NASA's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), combined with high-resolution stereo images taken by NASA's HiRISE camera. Both instruments fly aboard NASA's Mars Reconnaissance Orbiter.

Of those 633 peaks, Milliken and Sun found 265 that have evidence of hydrated minerals, the majority of which were consistent with clays. The researchers then used HiRISE images to establish a detailed geologic context for each of those craters to help determine if the clays were in rocks that had indeed been excavated from depth. They found that in about 65 percent of cases the clay minerals were indeed associated with uplifted bedrock.

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Evidence of Periglacial Areological Artifacts From Late Amazonian Glaciations on Mars

Sorted (clastic) polygons in the Argyre region, Mars, and possible evidence of pre- and post-glacial periglaciation in the Late Amazonian Epoch

Authors:

Soare et al

Abstract:

The Argyre basin and associated rim-materials in the southern highlands of Mars are ancient, having been formed by the impact of a large body ∼3.9 Gya. Despite its age, the regional landscape exhibits a wide range of geological/geomorphological modifications and/or features, e.g. fluvial, lacustrine, aeolian, glacial and periglacial. Collectively, this bears witness to the dynamic evolution of the Argyre region from the deep past through to, perhaps, the present day.

Here, we present three principal findings that point to at least two distinct episodes of periglaciation, separated by a possible glacial-interval, during the very Late Amazonian Epoch in eastern Aonia Terra (AT), i.e. on the western flank of the Argyre basin. These findings are the product of our circum-Argyre study of all HiRISE images (∼35–65°S and ∼290–350°E).

(1)

(a) The first periglacial episode involves the development of small-sized (∼15–25 m in diam.) and clastically-“sorted polygons” (SPs). The SPs are observed at eighteen locations within eastern AT. Hitherto, the presence of SPs in this region has been reported at one location alone. No other observations of SPs in the southern hemisphere of Mars have been documented. Morphologically similar landforms develop in cold-climate (permafrost) landscapes on Earth by means of periglacial processes, i.e. freeze–thaw cycling, segregated-ice formation, cryoturbation and frost heave.

(b) We ascribe a periglacial origin to the SPs in eastern AT on the basis of this similarity of form and, no less importantly, on the close spatial-association of the SPs with blockfields (whose weathered “clastic” products are the building blocks of periglacial sorting on Earth), gelifluction-like lobes and possible “wet” gullies. Where similar assemblages occur in terrestrial permafrost-landscapes, the presence of liquid water and of boundary conditions tolerant of freeze–thaw cycling, are observed or inferred.

(c) Fifteen of the eighteen SP locations are clustered longitudinally (44.4–57.5°S; 289.9–302.4°E). This is inconsistent with the latitudinal- and (obliquity-driven) dependency of freeze–thaw cycling in the Late Amazonian Epoch hypothesised by many workers in the discipline.

(2) The second periglacial episode is highlighted by the development of small-sized and clastically non-sorted polygons (NSPs). These polygons could have formed by means of a “dry” cryotic process, i.e. thermal-contraction cracking.

(3) The NSPs incise (and thus postdate) a light-toned mantle, thought by numerous workers to comprise an “ice-dust” admixture. At some of the locations where the putatively icy-mantle has undergone apparent ablation, underlying SPs are observed. This suggests that the SPs predate the mantle and, derivatively, the NSPs as well.

The proposed geochronology of “wet-based SP – icy mantle – dry-based NSP” (periods and interval) is entirely new to the community. Moreover, it underlines the possibility that periglacial and glacial boundary-conditions, at least in our study area, may have oscillated much more substantially in the very Late Amazonian Epoch than many workers have thought possible.

Evidence of Enhanced Erosion During Amazonian Eon Glaciations on Mars

Enhanced erosion rates on Mars during Amazonian glaciation

Authors:

Levy et al

Abstract:

Observations of Mars from the surface and from orbit suggest that erosion rates over the last ∼3 Gyr (the Amazonian) have been as slow as 10−5 m/Myr and have been dominated by aeolian processes, while ancient (Noachian) erosion rates may have been orders of magnitude higher due to impact bombardment and fluvial activity. Amazonian-aged glacial deposits are widespread on Mars, but rates of erosion responsible for contributing debris to these remnant glacial deposits have not been constrained. Here, we calculate erosion rates during Amazonian glaciations using a catalog of mid-latitude glacial landforms coupled with observational and theoretical constraints on the duration of glaciation. These calculations suggest that erosion rates for scarps that contributed debris to glacial landforms are 4–7 orders of magnitude higher than average Amazonian rates in non-glaciated, low-slope regions. These erosion rates are similar to terrestrial cold-based glacier erosion and entrainment rates, consistent with cold-based glacier modification of parts of Mars.

Recent Climate Cycles on Mars

Recent climate cycles on Mars: Stratigraphic relationships between multiple generations of gullies and the latitude dependent mantle

Authors:

Dickson et al

Abstract:

Reconstructions of the orbital parameters of Mars spanning the last ∼20 Myr, combined with global circulation models, predict multiple cycles of accumulation and degradation of an ice-rich mantle in the mid-latitudes, driven primarily by insolation at the poles during periods when obliquity was more than ten degrees greater than it is today (i.e., >∼35°). While evidence of an ice-rich “latitude dependent mantle” (LDM) consistent with these predictions is abundant, features indicative of cycles of emplacement and degradation of this unit are isolated and rare. In addition, fundamental physical properties of the LDM, such as paleo-thickness maxima, have not been determined. Gullies, which are sinuous channels found on steep slopes in mid- and high-latitudes, interact with the LDM and provide a stratigraphic feature useful for documenting both cyclical emplacement/removal and thickness estimates in past climate regimes. In the southern hemisphere, where gullies are most common, we present extensive evidence of (1) cyclical degradation and removal of gullies in the lower mid-latitudes (30–40°S), and (2) burial and exhumation of inverted gully channels in the transitional latitude band between dissected and preserved LDM (40–50°S), which can only be accounted for if an additional tens of meters of LDM were present at these locations during channel formation. These relationships support a model in which end-to-end gully evolution is controlled by the behavior of the LDM: at lower latitudes, gullies incise an ice-rich substrate and are removed when that ice becomes unstable, and at higher latitudes gullies are buried by successive emplacement of LDM where ice remains stable near the surface. Further, the presence of dormant buried gullies implies that present-day activity within gullies, likely to be controlled by the behavior of CO2 frost, is insufficient to explain the entire gully population, and that conditions conducive to increased gully activity preceded the most recent phase of LDM emplacement.

Volcanic Induced Deglaciation on Arsia Mons During Late Amazonian

Volcanism-induced, local wet-based glacial conditions recorded in the Late Amazonian Arsia Mons tropical mountain glacier deposits

Authors:

Scanlon et al

Abstract:

The tropical mountain glacial fan-shaped deposit (FSD) to the northwest of the Arsia Mons volcano on Mars contains numerous glacial and volcanic landforms. While most of the glacial landforms are interpreted to have formed by cold-based glacial processes, several glacial landforms near glaciovolcanic edifices are more consistent with localized wet-based glacial processes. These landforms include ribbed moraines, which suggest local, thermal transitions between wet- and cold-based ice; thrust-block moraines, whose formation is typically assisted by the presence of subglacial water; streamlined knobs that we interpret to have been sculpted by ice sliding along its base; and a braided outflow channel. The presence and association of these features, together with evidence of both subglacial volcanic eruptions and local ice-marginal advances, favor polythermal glaciers with localized wet-based conditions. We propose that lava-to-ice heat transfer during the eruption of the glaciovolcanic edifices caused the Arsia Mons paleoglacier to melt at its base in some areas, resulting in these locally wet-based glacial conditions. A polythermal glacier provides more potential microbial habitats and more connectivity between habitats than does a cold-based glacier, and we review glacial and glaciovolcanic habitats on Earth that may provide insight into the likelihood of potential microbial habitats within the Arsia Mons FSD on Mars.

Evidence the Martian South Polar Plateau Radically Shrank During the Late Amazonian

New insights into the Late Amazonian zonal shrinkage of the martian south polar plateau

Authors:

Rodriguez et al

Abstract:

The martian south polar plateau, Planum Australe, comprises the largest known water–ice surface deposit on the planet. Here, we present evidence for an episode of extensive polar plateau retreat during the Late Amazonian, which affected regions flanking circum-polar terrains located between Cavi Angusti and Sisyphi Montes.

Amazonian Eon Thermokarst in the Danielson Crater of Arabia Terra on Mars

Amazonian thermokarst in Danielson crater, Arabia Terra region, Mars

Authors:

Baioni et al

Abstract:

This paper describe the possible ice-related landforms observed within Danielson crater which is centered at about 8°N and 353°E, in the region of southwestern Arabia Terra about 800 km south of Becquerel crater.

A morphological survey of the study area through an analysis of the available Mars images was performed. The features of the landforms were investigated through an integrated analysis of Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) data.

Landforms interpreted as due to thermokarst processes, resembling similarly ice-related landforms found both in the cold-climate non-glacial regions of Earth, and putatively in other areas of Mars, was observed.

These landforms are attributed to the presence of ground ice/ice-melting processes reflect significant climatic changes and different climatic conditions than those existing now. Moreover, they appear to display young erosional age, suggesting that are probably young, probably of Amazonian age.

Episodic and Recent Glaciation in the Protonilus Mensae Region During the Amazonian

Amazonian modification of Moreux crater: Record of recent and episodic glaciation in the Protonilus Mensae region of Mars

Authors:

Sinha et al

Abstract:

Morphologic characteristics of ice-rich landforms in the martian mid-latitudes record evidence for significant modification of the landscape in response to spin–axis/orbital parameter-driven shifts in the Late Amazonian climate. These landforms are spatially distributed across the mid-latitudes and their co-existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while Mars was undergoing major–moderate–minor shifts in its Late Amazonian climate. We have therefore carried out an in-depth investigation of Moreux crater (∼135 km, centered at 41.66°N, 44.44°E in the Protonilus Mensae region) for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater. Evidence for extensive modification of the surfaces over crater rim/wall and around central peak by emplacement of multiple scales of ice-rich landforms that represents large history of glacial activities was found. From our results we document phases of major–moderate–minor glacial activities within the crater as: (1) piedmont lobes/lobate debris aprons/linear valley fills (∼1 Ga–100 Ma), (2) viscous flow features (∼30–0.1 Ma) and (3) gullies/thermal contraction crack polygons (∼2.1–0.4 Ma). The form and distribution of the random valleys observed within Moreux suggests their formation by pressure-induced melting and flow occurring beneath an extensive layer of ice. We also suggest that central peak of Moreux probably acted as the locus for accumulation of ice/snow and the diversity of glacial/periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice/snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes. Taken together, these ice-rich deposits within Moreux suggest that sequential modification of the crater surfaces over the rim/wall and around central peak has occurred over the last tens of millions of years of martian history. This new evidence thus adds another well-documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of Mars in recent martian history.

Evidence of Lake Missoula-like Glacial Lake Drainage From Mid Amazonian Chryse Planitia, Mars

Evidence for Middle Amazonian catastrophic flooding and glaciation on Mars

Authors:

Rodríguez et al

Abstract:

Early geologic investigations of Mars revealed some of the largest channels in the Solar System (outflow channels), which appear to have mostly developed ∼3 byr ago. These channels have been the subject of much scientific inquiry since the 1970s and proposed formative processes included surface erosion by catastrophic floods, glaciers, debris flows and lava flows. Based on the analysis of newly acquired Mars Reconnaissance Orbiter (MRO) Context (CTX, 5.15–5.91 m/pixel) and High Resolution Imaging Science Experiment (HiRISE, 25–50 cm/pixel) image data, we have identified a few locations contained within relatively narrow canyons of the southern circum-Chryse outflow channels that retain well-preserved decameter/hectometer-scale landform assemblages. These terrains include landforms consistent in shape, dimension and overall assemblage to those produced by catastrophic floods, and at one location, to glacial morphologies. Impact crater statistics for four of these surfaces, located within upstream, midstream and downstream outflow channel surfaces, yield an age estimate of ∼600 myr. This suggests that the southern circum-Chryse outflow channels were locally resurfaced by some of the most recent catastrophic floods on the planet, and that these floods coexisted within regional glacier environments as recently as during the Middle Amazonian.

What *IS* the Banded Terrain in the Martian Hellas Basin

The geomorphology and morphometry of the banded terrain in Hellas basin, Mars

Authors:

Diot et al

Abstract:

Hellas basin is a large impact basin situated in the southern highlands of Mars. The north-western part of the basin has the lowest elevation (−7.5 km) on the planet and contains a possibly unique terrain type, which we informally call “banded terrain”. The banded terrain is made up of smooth-looking banded deposits that display signs of viscous behavior and a paucity of superimposed impact craters. In this study, we use newly acquired high spatial resolution images from the High Resolution Imaging Science Experiment (HiRISE) in addition to existing datasets to characterize the geomorphology, the morphometry and the architecture of the banded terrain. The banded terrain is generally confined to the NW edge of the Alpheus Colles plateau. The individual bands are ∼3–15 km-long, ∼0.3 km-wide and are separated by narrow inter-band depressions, which are ∼65 m-wide and ∼10 m-deep. The bands display several morphologies that vary from linear to concentric forms. Morphometric analysis reveals that the slopes along a given linear or lobate band ranges from 0.5° to 15° (average ∼6°), whereas the concentric bands are located on flatter terrain (average slope ∼2–3°). Crater-size frequency analysis yields an Amazonian-Hesperian boundary crater retention age for the terrain (∼3 Gyr), which together, with the presence of very few degraded craters, either implies a recent emplacement, resurfacing, or intense erosion. The apparent sensitivity to local topography and preference for concentrating in localized depressions is compatible with deformation as a viscous fluid. In addition, the bands display clear signs of degradation and slumping at their margins along with a suite of other features that include fractured mounds, polygonal cracks at variable size-scales, and knobby/hummocky textures. Together, these features suggest an ice-rich composition for at least the upper layers of the terrain, which is currently being heavily modified through loss of ice and intense weathering, possibly by wind.

Long Term Northern Hemisphere Glaciation on Mars in Middle to Late Amazonian

An extended period of episodic northern mid-latitude glaciation on Mars during the Middle to Late Amazonian: Implications for long-term obliquity history

Authors:

Fassett et al

Abstract:

Mars is the only planet other than Earth in the Solar System that has a preserved nonpolar geological record of glaciation on its surface. Nonpolar ice deposits on Mars have been linked to variations in spin-axis obliquity that cause mobilization of polar ice and redeposition at lower latitudes, forming ice-rich and glacial deposits. Remnant nonpolar glacial deposits are found across the northern mid-latitudes where surface ice is not currently stable, implying that different climatic conditions existed on Mars in the past. Individual glacial deposits are often too small to date reliably using impact crater size-frequency data. We describe a novel approach that allows us to derive new information about when glaciation occurred in broad areas of the northern mid-latitudes. In this region we have classified (1) craters that superpose preexisting glacial deposits and were modified by later accumulation (and therefore formed during an epoch when glaciation was occurring), and (2) craters that are superposed on glacial deposits but are themselves unmodified by ice accumulation (and thus post-date significant glaciation). The sparse population of post-glacial craters reveals that the last period of extensive ice deposition of this type in this latitude band was recent (Late Amazonian). The substantial number of craters formed during the recurring glacial periods implies that northern mid-latitude glaciation was a long-lived recurring process, occurring over a period of at least ∼600 m.y. On the basis of Mars atmospheric general circulation models, these results are consistent with higher obliquity being common in the past, with recurring periods of obliquity exceeding the 25° axial tilt of Mars today. These observations support the statistical prediction of J. Laskar and colleagues that the median obliquity during the Amazonian was ∼35°–40°.

Mars was Only Emphemerally Habitable

Water and Martian Habitability: Results of an Integrative Study of Water Related Processes on Mars in Context with an interdisciplinary Helmholtz Research Alliance “Planetary Evolution and Life”

Authors:

Juamann et al

Abstract:

A study in context with the Helmholtz Alliance ‘Planetary Evolution and Life’ focused on the (temporary) existence of liquid water, and the likelihood that Mars has been or even is a habitable planet. Both geomorphological and mineralogical evidence point to the episodic availability of liquid water at the surface of Mars, and physical modeling and small-scale observations suggest that this is also true for more recent periods. Habitable conditions, however, were not uniform over space and time. Several key properties, such as the availability of standing bodies of water, surface runoff and the transportation of nutrients, were not constant, resulting in an inhomogeneous nature of the parameter space that needs to be considered in any habitability assessment. The planetary evolution of Mars led to environmental changes, which in turn affected its habitability potential. Similarly, considerable variations in climate due to latitudinal or elevation effects combined with a diverse surface geology caused distinctively different local conditions that influenced the planet's habitable potential.

More Evidence of a Near Snowball Mars in the Martian Amazonian Eon?

Amazonian Mid- to High-Latitude Glaciation on Mars:Supply-Limited Ice Sources, Ice Accumulation Patterns, and Concentric Crater Fill Glacial Flow and Ice Sequestration

Authors:

Fastook et al

Abstract:

Concentric Crater Fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about 1) the maximum thickness of regional ice deposits during the Late Amazonian, 2) the likelihood that these deposits flowed regionally, 3) the geological regions and features most likely to induce ice-flow, and 4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted.

Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal Crater deposit thicknesses (∼50 m) cannot fill the craters in a time period compatible with the interpreted formation times of the Pedestal Crater mantled ice layers. We use a representative obliquity solution to drive an ice flow model and show that a cyclical pattern of multiply recurring layers can both fill the craters with a significant volume of ice, as well as transport debris from the crater walls out into the central regions of the craters. The cyclical pattern of waxing and waning mantling layers results in a rippled pattern of surface debris extending out into the crater interiors that would manifest itself as an observable concentric pattern, comparable in appearance to concentric crater fill. In this scenario, the formation of mantling sublimation till layers seals the accumulating ice and sequesters it from significant temperature variations at diurnal, annual and spin-axis/orbital cycle time scales, to produce ancient ice records preserved today below CCF crater floors.

Lack of meltwater features associated with concentric crater fill provides evidence that the Late Amazonian climate did not exceed the melting temperature in the mid- to high-latitudes for any significant period of time. Continued sequestration of ice with time in CCF and related deposits (lobate debris aprons and lineated valley fill) further reduces the already supply-limited polar ice sources, suggesting that there has been a declining reservoir of available ice with each ensuing glacial period. Together, these deposits represent a candidate library of climate chemistry and global change dating from the Late Amazonian, and a non-polar water resource for future exploration.

More Evidence of Middle to Late Amazonian Mountain Glaciers on Mars

Middle to Late Amazonian Tropical Mountain Glaciers on Mars: The Ages of the Tharsis Montes Fan-Shaped Deposits

Authors:

Kadish et al

Abstract:

Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35°S, ~125 Ma for the Pavonis FSD at 1.48°N, and ~210 Ma for the Arsia FSD at 11.92°N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45–150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 105 km3) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined CSFD ages of three adjacent drop moraine units at Arsia Mons (725 Ma, 475 Ma and 345 Ma) and used these to calculate the average amount of time needed to form one of the approximately 185 drop moraines forming these deposits; we found that a typical drop moraine formation time in the Arsia FSD ridged facies to be on the order of ~106 years. These formation ages are considerably longer than that required for typical moraine systems alongside dynamic, wet-based glaciers on Earth, but are in approximate accord with recent geomorphological and geochemical data that document long-term, ice-margin stability for several cold-based glaciers in interior Antarctica. The difference in the ages of the ridged facies and non-ridged portion of the Arsia FSD suggests that the tropical mountain glaciers may have been emplaced over a period spanning many hundreds of millions of years. CSFD measurements for lava flows predating and postdating the Arsia Mons FSD suggest a maximum possible age of less than 750 Ma and a minimum age for the late stage, post FSD lava flows of ~105 Ma. Taken together, this evidence supports a scenario in which ice has been present and stable in substantial quantities (~105–106 km3) at tropical latitudes during extended periods of the Middle to Late Amazonian history of Mars. This implies that during this time, Mars sustained periods of spin-axis obliquity in the vicinity of 45°, during which time polar ice deposits were substantially reduced in volume or perhaps even absent.

Evidence of a Late Amazonian "Snowball Mars" or Periodic Glaciations at Mid Latitudes?

The Ages of Pedestal Craters on Mars: Evidence for a Late-Amazonian Extended Period of Episodic Emplacement of Decameters-Thick Mid-Latitude Ice Deposits

Authors:

Seth J. Kadish and James W. Head

Abstract:

There is significant geomorphologic evidence for the past presence of longitudinally widespread, latitudinally zoned deposits composed of ice-rich material at northern and southern mid latitudes on Mars (lobate debris aprons, lineated valley fill, concentric crater fill, pedestal craters, etc.). Among these features, pedestal craters (Pd) are impact craters interpreted to have produced a protective layer on top of decameters-thick ice deposits now missing in intercrater regions. The time during which these various deposits were present is still highly debated. To address this question we have analyzed the distribution and characteristics of pedestal craters; here, we use a population of 2287 Pd to derive a crater retention age for the entire population, obtaining a minimum timescale of formation of ∼90 Myr. Given that the ice-rich deposit has not been continuously present for this duration, the timescale of formation is necessarily longer than ∼100 Myr. We then compiled impact crater size-frequency distribution dates for 50 individual pedestal craters in both hemispheres to assess further the frequency distribution of individual ages. We calculated pedestal crater ages that ranged from ∼1 Myr to ∼3.6 Gyr, with a median of ∼140 Myr. In addition, 70% of the pedestal ages are less than 250 Myr. During the 150 Myr period between 25 Ma and 175 Ma, we found at least one pedestal age every 15 Myr. This suggests that the ice-rich paleodeposit accumulated frequently during that time period. We then applied these results to the relationship between obliquity and latitudinal ice stability to suggest some constraints on the obliquity history of Mars over the past 200 Myr. Atmospheric general circulation models indicate that ice stability over long periods in the mid latitudes is favored by moderate mean obliquities in the ∼35° range. Models of spin-axis/orbital parameter evolution predict that the average obliquity of Mars is ∼38°. Our data represent specific observational evidence that ice-rich deposits accumulated frequently during the past 200 Myr, supporting the prediction that Mars was characterized by this obliquity range during an extensive part of that time period. Using these results as a foundation, the dating of other non-polar ice deposits will permit the specific obliquity history to be derived and lead to an assessment of volatile transport paths in the climate history of Mars.

Water in the Noctis Labyrinthus (Mars) From the Late Heserperian to Amazonian

Gypsum, Opal, and Fluvial Channels within a Trough of Noctis Labyrinthus, Mars: Implications for Aqueous Activity during the Late Hesperian to Amazonian

Authors:

1. Catherine M. Weitz (a)
2. Janice L. Bishop (b)
3. John A. Grant (c)

Affiliations:

a. Planetary Science Institute, 1700 E Fort Lowell, Suite 106, Tucson, AZ 85719

b. SETI/NASA AMES, 515 N. Whisman Rd., Mountain View, CA 94043

c. Smithsonian Institution, National Air and Space Museum, CEPS, MRC 315, Independence Ave. at 6th St SW, Washington, DC 20013

Abstract:

We investigate in detail the morphology, mineralogy, and stratigraphy of light-toned deposits within one trough of Noctis Labyrinthus, centered at −6.8°N, 261.1°E. CRISM spectra taken from light-toned layered deposits in the northern portion of the trough exhibit absorptions around 1.41, 1.92 and 2.21 μm, consistent with mixtures of opal and Al-clays that are exposed beneath younger lava flows and between high-standing mesas of chaotic terrain. In the southern portion of the trough, opal occurs as a patchy surficial deposit along the southeastern lower wall. Gypsum appears to be present in the southern portion of the trough where spectra show triplet absorptions at 1.44, 1.48, and 1.54 μm, and additional absorptions at 1.20, 1.74, 1.95, 2.22, 2.27, and 2.49 μm. The gypsum-bearing materials consist of one to several beds that typically fill low-lying regions, including valleys. A bright mound on the trough floor exhibits spectral features at 1.43, 1.92 and 2.43 µm, characteristic of polyhydrated sulfates. The bright mound appears distinct in morphology from chaotic terrain, and along its base are exposures of gypsum-bearing materials.

Fluvial channels in the southwestern portion of the trough incise surface slopes at 4–6° and lack obvious sources. The channels display first and second order tributaries arranged in a parallel pattern and may have formed by localized surface discharge from melting snow and/or ice. Both opal and gypsum occur in close proximity in the southwestern region of the trough, but gypsum is found alone in the southeast and opal in association with Al-clays is found to the northwest. We do not believe gypsum and opal formed coevally because they are not always found together, they require different aqueous conditions (i.e., opaline deposits require high silica availability while the gypsum deposits require high Ca availability in solution), and they appear at stratigraphically distinct levels. Although we identified evidence for fluvial landforms within the trough, cross-cutting relations indicate their incision post-dates deposition of the opal and pre-dates deposition of the gypsum. Hence, several periods of aqueous activity and alteration likely occurred within the trough from the Late Hesperian into the Amazonian that reflect favorable localized conditions within the Noctis Labyrinthus region and may be contemporaneous with late aqueous activity occurring elsewhere on Mars.