HR: 1340h
AN: P13B-1293    [Abstracts]
TI: Geomorphologic Interpretation of Southwest Arabia Terra, Mars: Evidence of Regional, Long- Duration Fluvial Activity
AU: * Salvatore, M R
EM: mrs5002@psu.edu
AF: Penn State University Department of Geography, 302 Walker Building, University Park, PA 16802, United States
AU: Allen, C C
EM: carlton.c.allen@nasa.gov
AF: National Aeronautics and Space Administration Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
AU: Oehler, D Z
EM: dorothy.z.oehler@nasa.gov
AF: National Aeronautics and Space Administration Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
AU: Wilkinson, J
EM: justin.wilkinson-1@nasa.gov
AF: National Aeronautics and Space Administration Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
AB: Southwest Arabia Terra, Mars, is home to seven candidate Mars Science Laboratory (MSL) landing sites and is immediately north of the Mars Exploration Rover (MER) Opportunity in Meridiani Planum. Some of the strongest evidence for the past presence of liquid water exists in this region: the strong hematite signals from Meridiani revealed by the Thermal Emission Spectrometer (TES) as well as evidence of layering and analyses of rocks that must have formed in the presence of water by Opportunity. To better understand this region and the context for the potential MSL landing sites, a detailed geologic map was produced during the summer of 2007. The numerous exposed layers present in southwest Arabia Terra reveal a vast history of deposition and erosion. Of particular interest is the widespread geologic unit containing sinuous, inverted ridges of varying lengths, widths, and orientations. This ridge-forming unit appears to have once been dominant throughout much of the study region. Since its original formation, deposition and erosion have obscured or removed sections of this unit to produce the fragmented and discontinuous pattern that we see today. Analyses of these inverted ridges suggest that they are sedimentary in nature and are likely to be the cemented and hardened remains of ancient stream channels. One analog we are considering is that of a terrestrial megafan. Megafans, which are relatively new concepts in geology, are onshore sedimentary features laid down by rivers over extended periods of time. They are defined as major, regional geomorphic forms (similar to alluvial fans) that are greater than 100 kilometers in radius and typically have a slope of less than 1º. They differ from alluvial fans in main stream behavior; streams in alluvial fans will quickly split into numerous smaller streams while streams that form megafans remain as one continuous stream. The comparison of the ridged-unit to a terrestrial megafan is based on several features including the braided nature, sinuosity, and cross-cutting relationships of the inverted channels as well as the regional distribution of the entire unit across a plain of extremely low slopes. The hypothesis that the ridged-unit may be a remnant of a megafan would imply that liquid water was present in this area for an extended period of time. This would be consistent with other features suggesting that Southwest Arabia Terra has experienced of a long history of aqueous conditions (e.g., abundant rampart craters, ramparts with varying degrees of erosion, regional setting likely to have received run-off from the southern highlands and from possible extensions of the major obvious outflow channels to the west, and high abundances of near-surface hydrogen as measured by gamma-ray spectroscopy on Mars Odyssey which suggest the presence of significant ice/ fluids in the subsurface). The interpretation of possible megafans in Southwest Arabia Terra has implications for habitability in the Martian past. Long episodes of liquid water indicate that a denser atmosphere must have existed. In addition, liquid water is necessary for life as we know it to exist. MSL landing site candidates, such as Vernal Crater which are clearly associated with this ridged-unit, may have enhanced chances of having been habitable in the past if the proper conditions to produce a megafan once existed on Mars. Work is continuing to evaluate this possibility.
DE: 5419 Hydrology and fluvial processes
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting