Post by Daniela Tirsch.
Glacial and fluvial landforms that date to ancient Noachian and Hesperian times indicate an abundance of liquid water on Mars at that time. Of interest is evidence of younger (i.e., Amazonian) glacial activities. These processes have recently been suggested for some locations in the Marmers Valles region of Mars [Kress et al., 2006; Di Achille and Ori, 2008; Tirsch, 2009a] (Image 1).
Marmers Valles tracks about 1000 km along the dichotomy boundary on Mars, near the Deuteronilus Mensae region. This region is characterized by “fretted terrain”, a term used for a surface having a stippled and pitted texture. This surface texture is proposed to have resulted from the partial removal of formerly smooth and thin deposits by deflation and sublimation [Carr, 2001].
Images of the crater and the valley entering the crater from the east (Image 2) show that flow structures dominate the morphology of the floor. They are interpreted as remnants of debris-covered glaciers, commonly known as lineated valley fills (LVF) [e.g. Dickson et al., 2006; Levy et al., 2007; Kress and Head, 2009; Morgan et al., 2009]. Other theories concerning the origin of the LVFs include ice-rich landslides [Carr, 2001] or rock glaciers [Mangold, 2003; Pierce and Crown, 2003]. Thus, these structures are evidence of glacial processes in northern Arabia Terra dated to the Amazonian period [Morgan et al., 2009]. Small rampart crater morphology in the vicinity of the crater (e.g. in the lower right corner of Image 1) confirm the former existence of water and ice in the subsurface [e.g. Carr et al., 1977; Wohletz and Sheridan, 1983]. The mesas at the center of this 30 km crater (Image 1) may be either remnant mountains or blocks that detached from the flanks and transported to the crater center.
The material in the low albedo area at the eastern crater rim is composed of mafic minerals, dominated by pyroxene (Image 3) [Tirsch et al., 2008]. This material is proposed to be ancient volcanic ash, either transported to the crater floor by aeolian processes or derived in situ from a dark layer exposed by erosion in the crater subsurface [Tirsch et al., 2009a, b].
Carr, M.H., L.S. Crumpler, J.A. Cutts, R. Greeley, J.E. Guest, and H. Masursky (1977): Martian impact craters and emplacement of ejecta by surface flow, Journal of Geophysical Research, 82, 4055-4065. [Abstract]
Carr, M.H. (2001): Mars Global Surveyor observations of Martian fretted terrain, Journal of Geophysical Research, 106, 23571-23594. [Abstract]
Dickson, J.L., J.W. Head, M.A. Kreslavsky, and D.R. Marchant (2006): Linear Lobate Debris Aprons, Piedmont-like Lobes, and Crater Fill in the Acheron Fossae Graben Region, Mars: Evidence for Debris-covered Glacier Formation and Flow, LPSC XXXVII, abstract #1321. [Abstract]
Kress, A. and J.W. Head (2009): Lineated Valley Fill and Lobate Debris Aprons in the Deuteronilus Mensae Region, Mars: Implications for Regional Glaciation, Lunar and Planetary Institute Science Conference Abstracts, abstract #1632. [Abstract]
Levy, Joseph S., James W. Head, and David R. Marchant (2007): Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary, Journal of Geophysical Research (Planets), 112, 08004. [Abstract]
Mangold, N. (2003): Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures, Journal of Geophysical Research(Planets), 108, 8021. [Abstract]
Morgan, G.A., J.W. Head, and D.R. Marchant (2009): Lineated valley fill (LVF) and lobate debris aprons (LDA) in the Deuteronilus Mensae northern dichotomy boundary region, Mars: Constraints on the extent, age and episodicity of Amazonian glacial events, Icarus, 202, 22-38. [Abstract]
Pierce, T.L. and D.A. Crown (2003): Morphologic and topographic analyses of debris aprons in the eastern Hellas region, Mars, Icarus, 163, 46-65. [Abstract]
Tirsch, D., R. Jaumann, F. Poulet, K.D. Matz, J.-P. Bibring, and G. Neukum (2008): A Global View on the Mineralogical Composition of Dark Dunes on Mars, LPSC XXXIX, abstract #1693. [Abstract]
Tirsch, D. (2009a): Dark Dunes on Mars – Analyses on Origin, Morphology and Mineralogical Composition of the Dark Material in Martian Craters., PhD thesis, 164 pp, Freie Universitaet Berlin, Berlin. [Abstract]
Tirsch, D., R. Jaumann, A. Pacifici, F. Poulet, L.H. Roach, J.F. Mustard, J.-P. Bibring, and G. Neukum (2009b): Dark Layers as Local Sources for the Dark Intra-Crater Dunes on Mars, LPSC XL, abstract #1004. [Abstract]
Wohletz, K.H. and M.F. Sheridan (1983): Martian rampart crater ejecta: Experiments and analysis of melt-water interaction, Icarus, 56, 15-37. [Abstract]
Image credit: ESA/DLR/FU Berlin (G. Neukum)