DOCSLIB.ORG

The Martian Drainage System and the Origin of Valley Networks and Fretted

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Martian Drainage System and the Origin of Valley Networks and Fretted JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. E4, PAGES 7479-7507, APRIL 25, 1995 The Martian drainage systemand the origin of valley networks and fretted channels Michael H. Cart U.S. Geological Survey, Menlo Park, California Abstract. Outflow channels provide strong evidence for abundant water near the Martian surface and an extensive groundwater system. Collapse of the surface into some channels suggestsmassive subsurfaceerosion and/or solution in addition to erosion by flow across the surface. Flat floors, steep walls, longitudinal striae and ridges, downstream deflection of striae from channel walls, and lack of river channels suggestthat fretted channelsform dominantly by mass wasting. A two-stage process is proposed. In the first stage, extension of valleys at valley heads is favored by seepage of groundwaterinto debris shedfrom slopes.The debris moves downstream,aided by interstitial groundwaterat the base of the debris, possiblywith high pore pressures.In the second stage, because of climate change or a lower heat flow, groundwater can no longer seep into the debris flows in the valleys, their movementalmost stops, and more viscousice-lubricated debris aprons form. Almost all uplandsat elevationsgreater than + 1 km are dissected by valley networks, although the drainage densities are orders of magnitudeless than is typical for the Earth. The valley networks resemble terrestrial river systemsin planimetric shape,but U-shaped and rectangular-shapedcross sections,levtelike peripheral ridges, median ridges, patterns of branching and rejoining, and flat floors without river channelssuggest that the networks may not be true analogs to terrestrial river valleys. It is proposed that they, like the fretted channels, formed mainly by mass wasting, aided by groundwater seepageinto the mass-wasteddebris. Movements of only millimeters to centimetersper year are needed to explain the channel lengths. Most valley formation ceased early at low latitudes becauseof progressivedehydration of the near surface, the result of sublimation of water and/or drainageof groundwaterto regionsof lower elevations.Valley formation persistedto later dates where aided by steep slopes,as on crater and canyon walls, and/or by high heat flows and the presenceof water, as on some volcanoes. Introduction wastinghas played a prominent, if not dominant, role in their formation. On the Martian surface are a variety of drainagefeatures This reevaluation of the distribution and characteristics of that have generally been attributed to water erosion. This the various drainage features of Mars has been triggered by paper describes the drainage system of Mars and discusses several recent developments. It was recognized early that what might be inferred from the characteristics of the most of the valley networks are old and that, for their system. The main concern is to reassesswhat processes formation, they probably required climatic conditionssignif- caused formation of the drainage system, so that the re- icantly warmer than present conditions.This led to a simple quired climatic conditions can be subsequentlyevaluated. model for the climatic evolution of Mars in which early Mars The valley networks receive the most attention becausetheir was warm and wet and had a thick CO2 atmosphere, but presence has been viewed as the strongest evidence for soon after the end of heavy bombardment, the atmosphere warm and wet climatic conditionsin the past. The outflow lost most of its CO2 due to formation of carbonates, and channelsand fretted channelsare also discussed,mainly to surface conditions changed to those that we observe today illuminate someissues that might have bearing on the origin [Pollack, 1979; Pollack et al., 1987; Fanale et al., 1992]. This of the networks. The paper is partly descriptive.It describes simple model is now being challenged on several grounds. the different elements of the Martian drainage system, em- While most of the networks do indeed occur in the oldest phasizing various properties that must be explained by terrains (Noachian), a significant fraction may be younger models for its origin. Other parts of the paper are more than Noachian [Scott and Dohm, 1992], and some networks, speculative, as different possibilities for the origin of the notably those on Alba Patera, formed relatively late in drainagefeatures, particularly the networks, are discussed. Martian history [Mouginis-Mark et al., 1988; Scott and One general conclusion is that the valley networks are unlikely to be composed mostly of fluvial valleys, as has Tanaka, 1986]. It has also been hypothesizedthat Mars has been widely assumed. The second conclusion is that mass experienced recurrent glaciations, some relatively late in its history [Kargel and Strom, 1992]. If so, then precipitation This paperis not subjectto U.S. copyfight.Published in 1995by the and climatic conditions very different from those that pres- American Geophysical Union. ently prevail occurred late. Baker et al. [1991], noting the Paper number 95JE00260. late-forming networks, the late-occurring glaciations, and 7479 7480 CARR: MARTIAN DRAINAGE SYSTEM, VALLEY NETWORKS, FRETTED CHANNELS evidence for former, large bodies of water in the northern of these alternatives have, however, appeared as plausibleas plains [Lucchitta et al., 1986; Parker et al., 1989; Chapman, water erosion (for summaries, see Carr [1981] and Baker 1994], suggestedthat, episodically, throughout Martian his- [1982, 1985], and water is now almost universally taken as tory, catastrophic floods left ocean-sizedbodies of water in the most likely erosive agent in the formation of the valleys low-lying areas. They hypothesizedthat these oceanscaused and channels. The linear erosional features of Mars have major changesin the global climate, that these changeswere generally been divided into three classes [Sharp and Malin, short lived, but that during the short warm periods, the 1975; Carr, 1981; Baker, 1982]. Most outflow channels start hypothesized glacial features and young networks formed. full size, have few if any tributaries, and commonly have The supposition of a warm, wet Mars changing irrevers- bedforms, such as scour marks, on their floors. What have ibly to the present Mars through loss of a thick CO2 been called valleys start small, increase in size downstream, atmosphere has also been challenged on other grounds. and form branching networks. Fretted channels are broad, First, there is little, if any, definitive spectroscopicevidence flat-floored valleys that commonly branch upstream, widen of young carbonate deposits at the surface [Blaney and downstream, and contain abundant evidence of mass wast- McCord, 1989], althoughPollack et al. [1990] detected 1-3% ing from their walls. carbonatesin dust in the atmosphere, and Calvin et al. [ 1994] The initial reluctanceto accept water as the erosive agent interpret a spectral feature at 4.5 tamthat might be indicative stemmed from the stability relations of water at the Martian of 10-20% hydrous magnesium carbonate. If the networks surface. Under present climatic conditions, with mean an- are to be attributed to a thick CO2 atmosphere,the carbon- nual temperatures of 215øK at the equator and 150øKat the ate deposits should be at the surface. Second, recent green- poles, the ground is permanently frozen to a depth of roughly house calculations suggest that a thick CO2 atmosphere 2-3 km at the equator and 4-7 km at the poles [Fanale, 1976; could not cause surface temperatures to rise to above 273øK Clifford, 1993]. The exact depth depends on the heat flow because of the formation of clouds, even with the present and the thermal conductivities of the crustal materials. Thus solar constant [Kasting, 1991]. The problem is further exac- liquid water is unstable everywhere on the planet within 1 erbated for early Mars because of the likelihood of a signif- km of the surface. At latitudes less than about 30ø, temper- icantly lower solar constant. Third, 'it has been suggested atures may be above the frost point at all depths, so that any that networks could form under present climatic conditions ice in the permafrost zone will slowly sublime into the by groundwater sapping [Squyres, 1989], as a result of atmosphere. The rates will be largely controlled by the rates hydrothermal activity [Gulick and Baker, 1989], or by flow of of diffusionof water vapor through the surface materials into water under thick ice covers [Wallace and Sagan, 1979]. the atmosphere [Farmer and Dams, 1979]. Under present These developments suggest a need to reevaluate the climatic conditions therefore water ice is unstable in much of observational data that have led to proposals of climate the permafrost zone at low latitudes. The instability of ice at change. Suggestionsfor former, distinctively different, cli- low latitudes has led to the suppositionthat the near-surface matic conditions on Mars are based largely on the valley materials have progressivelylost any ice that was originally networks and the supposition that because, in planimetric present, as a dehydrationfront moves to greater depthswith form, they resemble terrestrial river valleys, they require time [Clifford and Hillel, 1983; Fanale et al., 1986]. Ice terrestriallike climatic conditions for their formation. Yet, stability is, however, affected by variations in the thermal although numerous papers have been written about specific inertia, albedo, and permeability of the surface materialsand features or areas, there exists no comprehensive,up-to-date
Load more

Recommended publications
  • Thermal Studies of Martian Channels and Valleys Using Termoskan Data
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 99, NO. El, PAGES 1983-1996, JANUARY 25, 1994 Thermal studiesof Martian channelsand valleys using Termoskan data BruceH. Betts andBruce C. Murray Divisionof Geologicaland PlanetarySciences, California Institute of Technology,Pasadena The Tennoskaninstrument on boardthe Phobos '88 spacecraftacquired the highestspatial resolution thermal infraredemission data ever obtained for Mars. Included in thethermal images are 2 km/pixel,midday observations of severalmajor channel and valley systems including significant portions of Shalbatana,Ravi, A1-Qahira,and Ma'adimValles, the channelconnecting Vailes Marineris with HydraotesChaos, and channelmaterial in Eos Chasma.Tennoskan also observed small portions of thesouthern beginnings of Simud,Tiu, andAres Vailes and somechannel material in GangisChasma. Simultaneousbroadband visible reflectance data were obtainedfor all but Ma'adimVallis. We find thatmost of the channelsand valleys have higher thermal inertias than their surroundings,consistent with previousthermal studies. We show for the first time that the thermal inertia boundariesclosely match flat channelfloor boundaries.Also, butteswithin channelshave inertiassimilar to the plainssurrounding the channels,suggesting the buttesare remnants of a contiguousplains surface. Lower bounds ontypical channel thermal inertias range from 8.4 to 12.5(10 -3 cal cm-2 s-1/2 K-I) (352to 523 in SI unitsof J m-2 s-l/2K-l). Lowerbounds on inertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5 (46 to 147 sr). Atmosphericand geometriceffects are not sufficientto causethe observedchannel inertia enhancements.We favornonaeolian explanations of the overall channel inertia enhancements based primarily upon the channelfloors' thermal homogeneity and the strongcorrelation of thermalboundaries with floor boundaries. However,localized, dark regions within some channels are likely aeolian in natureas reported previously.
    [Show full text]
  • Evidence for Volcanism in and Near the Chaotic Terrains East of Valles Marineris, Mars
    43rd Lunar and Planetary Science Conference (2012) 1057.pdf EVIDENCE FOR VOLCANISM IN AND NEAR THE CHAOTIC TERRAINS EAST OF VALLES MARINERIS, MARS. Tanya N. Harrison, Malin Space Science Systems ([email protected]; P.O. Box 910148, San Diego, CA 92191). Introduction: Martian chaotic terrain was first de- ple chaotic regions are visible in CTX images (Figs. scribed by [1] from Mariner 6 and 7 data as a “rough, 1,2). These fractures have widened since the formation irregular complex of short ridges, knobs, and irregular- of the flows. The flows overtop and/or bank up upon ly shaped troughs and depressions,” attributing this pre-existing topography such as crater ejecta blankets morphology to subsidence and suggesting volcanism (Fig. 2c). Flows are also observed originating from as a possible cause. McCauley et al. [2], who were the fractures within some craters in the vicinity of the cha- first to note the presence of large outflow channels that os regions. Potential lava flows are observed on a por- appeared to originate from the chaotic terrains in Mar- tion of the floor as Hydaspis Chaos, possibly associat- iner 9 data, proposed localized geothermal melting ed with fissures on the chaos floor. As in Hydraotes, followed by catastrophic release as the formation these flows bank up against blocks on the chaos floor, mechanism of chaotic terrain. Variants of this model implying that if the flows are volcanic in origin, the have subsequently been detailed by a number of au- volcanism occurred after the formation of Hydaspis thors [e.g. 3,4,5]. Meresse et al.
    [Show full text]
  • Drainage Network Development in the Keanakāko'i
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, E08009, doi:10.1029/2012JE004074, 2012 Drainage network development in the Keanakāko‘i tephra, Kīlauea Volcano, Hawai‘i: Implications for fluvial erosion and valley network formation on early Mars Robert A. Craddock,1 Alan D. Howard,2 Rossman P. Irwin III,1 Stephen Tooth,3 Rebecca M. E. Williams,4 and Pao-Shin Chu5 Received 1 March 2012; revised 11 June 2012; accepted 4 July 2012; published 22 August 2012. [1] A number of studies have attempted to characterize Martian valley and channel networks. To date, however, little attention has been paid to the role of lithology, which could influence the rate of incision, morphology, and hydrology as well as the characteristics of transported materials. Here, we present an analysis of the physical and hydrologic characteristics of drainage networks (gullies and channels) that have incised the Keanakāko‘i tephra, a basaltic pyroclastic deposit that occurs mainly in the summit area of Kīlauea Volcano and in the adjoining Ka‘ū Desert, Hawai‘i. The Keanakāko‘i tephra is up to 10 m meters thick and largely devoid of vegetation, making it a good analog for the Martian surface. Although the scales are different, the Keanakāko‘i drainage networks suggest that several typical morphologic characteristics of Martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics. Many gully headwalls and knickpoints within the drainage networks are amphitheater shaped, which results from strong-over-weak stratigraphy. Beds of fine ash, commonly bearing accretionary lapilli (pisolites), are more resistant to erosion than the interbedded, coarser weakly consolidated and friable tephra layers.
    [Show full text]
  • Review of the MEPAG Report on Mars Special Regions
    THE NATIONAL ACADEMIES PRESS This PDF is available at http://nap.edu/21816 SHARE Review of the MEPAG Report on Mars Special Regions DETAILS 80 pages | 8.5 x 11 | PAPERBACK ISBN 978-0-309-37904-5 | DOI 10.17226/21816 CONTRIBUTORS GET THIS BOOK Committee to Review the MEPAG Report on Mars Special Regions; Space Studies Board; Division on Engineering and Physical Sciences; National Academies of Sciences, Engineering, and Medicine; European Space Sciences Committee; FIND RELATED TITLES European Science Foundation Visit the National Academies Press at NAP.edu and login or register to get: – Access to free PDF downloads of thousands of scientific reports – 10% off the price of print titles – Email or social media notifications of new titles related to your interests – Special offers and discounts Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the National Academies Press. (Request Permission) Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved. Review of the MEPAG Report on Mars Special Regions Committee to Review the MEPAG Report on Mars Special Regions Space Studies Board Division on Engineering and Physical Sciences European Space Sciences Committee European Science Foundation Strasbourg, France Copyright National Academy of Sciences. All rights reserved. Review of the MEPAG Report on Mars Special Regions THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 This study is based on work supported by the Contract NNH11CD57B between the National Academy of Sciences and the National Aeronautics and Space Administration and work supported by the Contract RFP/IPL-PTM/PA/fg/306.2014 between the European Science Foundation and the European Space Agency.
    [Show full text]
  • DID MARS EVER HAVE a LIVELY UNDERGROUND SCENE? Joseph
    Third Conference on Early Mars (2012) 7060.pdf DID MARS EVER HAVE A LIVELY UNDERGROUND SCENE? Joseph. R. Michalski, Natural History Mu- seum, London, UK and Planetary Science Institute, Tucson, AZ, USA. [email protected] Introduction: Prokaryotes comprise more than are investigating environments that might never have 50% of the Earth’s organic carbon, and the amount of been inhabited on a planet that is very much habitable. prokaryote biomass in the deep subsurface is 10-15 Spectroscopic results over the last 5-10 years have times the combined mass of prokaryotes that inhabit revealed significant diversity, abundance, and distribu- the oceans and terrestrial surface combined [1]. We do tion of alteration minerals that formed from aqueous not know when the first life occurred on Earth, but the processes on ancient Mars (recently summarized by first evidence is found in some of the oldest preserved Ehlmann et al. [6]). The mineralogy and context of rocks dating to 3.5 or, as much as 3.8 Ga [2]. While the these altered deposits indicates that deep hydrothermal concept of a “tree of life” breaks down in the Archean processes have operated on Mars, and might have per- [3], it seems likely that the most primitive ancestors of sisted from the Noachian into the Hesperian or later. In all life on Earth correspond to thermophile this work, I consider the implications of recent results chemoautotrophs. Perhaps these are the only life forms for the habitability of the subsurface, the occurrence of that survived intense heat flow during the Late Heavy groundwater, and the possibility to access materials Bombardment or perhaps they actually represent the representing subsurface biological processes.
    [Show full text]
  • New Chryse and the Provinces
    New Chryse and the Provinces The city of New Chryse is actually several connected cities. The Upper City is located on a break in the crater rim, looking down past a steep rock to the Lower City. Inside the da Vinci crater rim lies the Inner City, also known as the Old City – Red Era tunnels and cave shelters, as well as several nanocomposite towers and cupolas on Mona Lys Ridge looking down on the lower parts of the city. The Lower city lies in a valley sloping down to the Harbour City, which fills a crater 20 kilometres to the East. The Harbour City crater is connected to Camiling Bay and the sea through two canyons and is very well protected from both wind and ice. South of the Lower City and Harbour City lies The Slopes, a straight slope into the sea that is covered with sprawl and slums. Mona Lys Ridge is a mixture of palatial estates surrounded by gardens, imposing official imperial buildings and towering ancient structures used by the highest ranks of the Empire. The central imperial administration and especially the Council is housed in the Deimos Needle, a diamondoid tower that together with its sibling the Phobos Needle dominate the skyline. Escalators allow swift and discreet transport down to the lower levels of the city, and can easily be defended by the police force. North of Mona Lys lies a secluded garden city for higher administrators, guild officials and lesser nobility. The Inner City is to a large extent part of Mona Lys, although most of the inhabitants of Mona Lys do not care much for the dusty old tunnels and hidden vaults – that is left to the Guild of Antiquarians who maintain and protect it.
    [Show full text]
  • SPORADIC GROUNDWATER UPWELLING in DEEP MARTIAN CRATERS: EVIDENCE for LACUSTRINE CLAYS and CARBONATES. J. R. Michalski1,2, A. D. Rogers3, S
    SPORADIC GROUNDWATER UPWELLING IN DEEP MARTIAN CRATERS: EVIDENCE FOR LACUSTRINE CLAYS AND CARBONATES. J. R. Michalski1,2, A. D. Rogers3, S. P. Wright4, P. Niles5, and J. Cuadros1, 1Natural History Museum, London, UK 2Planetary Science Institute, Tucson, AZ, USA. 3SUNY Stony Brook, Stony Brook, NY, USA. 4University of New Mexico, Albuquerque, NM, USA. 5NASA Johnson Space Cen- ter, Houston, TX, USA. Introduction: While the surface of Mars may eralogy of deep impact craters was investigated using have had an active hydrosphere early in its history [1], TES, THEMIS, and CRISM data. it is likely that this water retreated to the subsurface Results: We identified ~40 craters of interest in the early on due to loss of the magnetic field and early northern hemisphere, the majority of which occur in atmosphere [2]. This likely resulted in the formation of western Arabia Terra – a potential upwelling zone of two distinct aqueous regimes for Mars from the Late interest [4]. Most of these craters do not contain obvi- Noachian onward: one dominated by redistribution of ous evidence for intra-crater aqueous activity, but surface ice and occasional melting of snow/ice [3], and ~10% contain interior channels and possible lacustrine one dominated by groundwater activity [4]. The exca- features. Most of the craters of interest are blanketed vation of alteration minerals from deep in the crust by by dust, which limits the possibilities for investigating impact craters points to an active, ancient, deep hydro- the mineralogy of intracrater deposits. thermal system [5]. Putative sapping features [6] may One clear exception is McLaughlin Crater (338.6 occur where the groundwater breached the surface.
    [Show full text]
  • Orbital Evidence for More Widespread Carbonate- 10.1002/2015JE004972 Bearing Rocks on Mars Key Point: James J
    PUBLICATIONS Journal of Geophysical Research: Planets RESEARCH ARTICLE Orbital evidence for more widespread carbonate- 10.1002/2015JE004972 bearing rocks on Mars Key Point: James J. Wray1, Scott L. Murchie2, Janice L. Bishop3, Bethany L. Ehlmann4, Ralph E. Milliken5, • Carbonates coexist with phyllosili- 1 2 6 cates in exhumed Noachian rocks in Mary Beth Wilhelm , Kimberly D. Seelos , and Matthew Chojnacki several regions of Mars 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA, 2The Johns Hopkins University/Applied Physics Laboratory, Laurel, Maryland, USA, 3SETI Institute, Mountain View, California, USA, 4Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA, 5Department of Geological Sciences, Brown Correspondence to: University, Providence, Rhode Island, USA, 6Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA J. J. Wray, [email protected] Abstract Carbonates are key minerals for understanding ancient Martian environments because they Citation: are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for Wray, J. J., S. L. Murchie, J. L. Bishop, paleoatmospheric CO2. Previous remote sensing studies have identified mostly Mg-rich carbonates, both in B. L. Ehlmann, R. E. Milliken, M. B. Wilhelm, Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older K. D. Seelos, and M. Chojnacki (2016), Orbital evidence for more widespread Fe- and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates carbonate-bearing rocks on Mars, are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between the Argyre – J.
    [Show full text]
  • Observations of the Marker Bed at Gale Crater with Recommendations for Future Exploration by the Curiosity Rover
    52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1484.pdf OBSERVATIONS OF THE MARKER BED AT GALE CRATER WITH RECOMMENDATIONS FOR FUTURE EXPLORATION BY THE CURIOSITY ROVER. C. M. Weitz1, J. L. Bishop2, B. J. Thomson3, K. D. Seelos4, K. Lewis5, I. Ettenborough3, and R. E. Arvidson6. 1Planetary Science Institute, 1700 East Fort Lowell, Tuc- son, AZ ([email protected]); 2SETI Institute, Carl Sagan Center, Mountain View, CA; 3Dept. of Earth and Planetary Sciences, Univ. Tennessee, Knoxville, TN; 4Planetary Exploration Group, JHU Applied Physics Laboratory, Laurel, MD; 5Dept Earth and Planetary Sciences, John Hopkins University, Baltimore, MD; 6Dept Earth and Planetary Sci- ences, Washington University, St. Louis, Missouri. Introduction: A dark-toned marker bed is ob- pearance across the mound. Most of the sulfates served within the sulfates at Gale crater [1,2]. This above/below the marker bed are stratified, heavily marker bed is characterized by a dark-toned, smooth fractured, and erode into boulder-size blocks, but there surface that appears more indurated and retains more are examples where the sulfates appear massive with craters relative to the sulfate-bearing layers above and limited fracturing and no boulders eroding from the below it. The bed has a distinct physical appearance unit (Fig. 3a). from the sulfates in which it occurs, suggesting a change in the environment or geochemistry for a brief period of time within the depositional sequence that formed the sulfates or post-deposition alteration. In this study, we utilized HiRISE and CTX images to identify and map the occurrence of the marker bed throughout Aeolis Mons.
    [Show full text]
  • 16. Ice in the Martian Regolith
    16. ICE IN THE MARTIAN REGOLITH S. W. SQUYRES Cornell University S. M. CLIFFORD Lunar and Planetary Institute R. O. KUZMIN V.I. Vernadsky Institute J. R. ZIMBELMAN Smithsonian Institution and F. M. COSTARD Laboratoire de Geographie Physique Geologic evidence indicates that the Martian surface has been substantially modified by the action of liquid water, and that much of that water still resides beneath the surface as ground ice. The pore volume of the Martian regolith is substantial, and a large amount of this volume can be expected to be at tem- peratures cold enough for ice to be present. Calculations of the thermodynamic stability of ground ice on Mars suggest that it can exist very close to the surface at high latitudes, but can persist only at substantial depths near the equator. Impact craters with distinctive lobale ejecta deposits are common on Mars. These rampart craters apparently owe their morphology to fluidhation of sub- surface materials, perhaps by the melting of ground ice, during impact events. If this interpretation is correct, then the size frequency distribution of rampart 523 524 S. W. SQUYRES ET AL. craters is broadly consistent with the depth distribution of ice inferred from stability calculations. A variety of observed Martian landforms can be attrib- uted to creep of the Martian regolith abetted by deformation of ground ice. Global mapping of creep features also supports the idea that ice is present in near-surface materials at latitudes higher than ± 30°, and suggests that ice is largely absent from such materials at lower latitudes. Other morphologic fea- tures on Mars that may result from the present or former existence of ground ice include chaotic terrain, thermokarst and patterned ground.
    [Show full text]
  • Explosive Lava‐Water Interactions in Elysium Planitia, Mars: Geologic and Thermodynamic Constraints on the Formation of the Tartarus Colles Cone Groups Christopher W
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, E09006, doi:10.1029/2009JE003546, 2010 Explosive lava‐water interactions in Elysium Planitia, Mars: Geologic and thermodynamic constraints on the formation of the Tartarus Colles cone groups Christopher W. Hamilton,1 Sarah A. Fagents,1 and Lionel Wilson2 Received 16 November 2009; revised 11 May 2010; accepted 3 June 2010; published 16 September 2010. [1] Volcanic rootless constructs (VRCs) are the products of explosive lava‐water interactions. VRCs are significant because they imply the presence of active lava and an underlying aqueous phase (e.g., groundwater or ice) at the time of their formation. Combined mapping of VRC locations, age‐dating of their host lava surfaces, and thermodynamic modeling of lava‐substrate interactions can therefore constrain where and when water has been present in volcanic regions. This information is valuable for identifying fossil hydrothermal systems and determining relationships between climate, near‐surface water abundance, and the potential development of habitable niches on Mars. We examined the western Tartarus Colles region (25–27°N, 170–171°E) in northeastern Elysium Planitia, Mars, and identified 167 VRC groups with a total area of ∼2000 km2. These VRCs preferentially occur where lava is ∼60 m thick. Crater size‐frequency relationships suggest the VRCs formed during the late to middle Amazonian. Modeling results suggest that at the time of VRC formation, near‐surface substrate was partially desiccated, but that the depth to the midlatitude ice table was ]42 m. This ground ice stability zone is consistent with climate models that predict intermediate obliquity (∼35°) between 75 and 250 Ma, with obliquity excursions descending to ∼25–32°.
    [Show full text]
  • Pacing Early Mars Fluvial Activity at Aeolis Dorsa: Implications for Mars
    1 Pacing Early Mars fluvial activity at Aeolis Dorsa: Implications for Mars 2 Science Laboratory observations at Gale Crater and Aeolis Mons 3 4 Edwin S. Kitea ([email protected]), Antoine Lucasa, Caleb I. Fassettb 5 a Caltech, Division of Geological and Planetary Sciences, Pasadena, CA 91125 6 b Mount Holyoke College, Department of Astronomy, South Hadley, MA 01075 7 8 Abstract: The impactor flux early in Mars history was much higher than today, so sedimentary 9 sequences include many buried craters. In combination with models for the impactor flux, 10 observations of the number of buried craters can constrain sedimentation rates. Using the 11 frequency of crater-river interactions, we find net sedimentation rate ≲20-300 μm/yr at Aeolis 12 Dorsa. This sets a lower bound of 1-15 Myr on the total interval spanned by fluvial activity 13 around the Noachian-Hesperian transition. We predict that Gale Crater’s mound (Aeolis Mons) 14 took at least 10-100 Myr to accumulate, which is testable by the Mars Science Laboratory. 15 16 1. Introduction. 17 On Mars, many craters are embedded within sedimentary sequences, leading to the 18 recognition that the planet’s geological history is recorded in “cratered volumes”, rather than 19 just cratered surfaces (Edgett and Malin, 2002). For a given impact flux, the density of craters 20 interbedded within a geologic unit is inversely proportional to the deposition rate of that 21 geologic unit (Smith et al. 2008). To use embedded-crater statistics to constrain deposition 22 rate, it is necessary to distinguish the population of interbedded craters from a (usually much 23 more numerous) population of craters formed during and after exhumation.
    [Show full text]