HR: 0800h
AN: P41A-0189    [Abstracts]
TI: Geology of the NW Rim of the Hellas Basin
AU: * Crown, D A
EM: crown@psi.edu
AF: Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, United States
AU: Bleamaster, L F
EM: lbleamas@psi.edu
AF: Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, United States
AU: Mest, S C
EM: mest@psi.edu
AF: Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, United States
AU: Mustard, J F
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912, United States
AB: Hellas is a significant region for evaluating volatile abundance, distribution, and cycling as well as changes in surface conditions on Mars, given the nature, diversity, and range in ages of potential water- and ice-related landforms. The highland terrains north of the basin have been of recent interest due to the discovery of phyllosilicates around and within impact craters. Current work focuses on the evolution of Hellas' NW rim, where an abrupt transition from basin floor deposits to circum-Hellas crater terrain is observed. Preliminary observations suggest that the NW Hellas rim can be divided into four zones that have different surface characteristics and lie in different elevation ranges: 1) Terra Sabaea highlands (above 500m), 2) Terra Sabaea plains (-2000m - 500m), 3) Hellas basin rim (-5800m - -2000m), and 4) Hellas Planitia/basin floor deposits (below -5800m). All of these zones show significant numbers of moderate to large impact craters, suggesting that the basic geologic framework of the region was established early in Martian history. However, there are clear differences in the types of landforms and materials exposed as well as differences in densities of large impact craters and crater degradation states. A significant and complex sedimentary history can be inferred given that many craters contain interior layered deposits, as well as by a multitude of scarps and valleys within intercrater plains. Crater interior deposits, typically exposed by irregular scarps, exhibit layering and clear differences in erosional morphology and thermophysical properties. We are characterizing the observed deposits and layered sequences, as well evaluating geologic and stratigraphic patterns in order to distinguish potential large-scale Hellas-centric systems from localized, spatially and/or temporally scattered depositional sinks. The zone of Terra Sabaea plains exhibits remnants of cratered highlands, including large infilled craters, within younger plains that appear to be part of a larger depositional shelf along Hellas' north rim. This zone is also at elevations similar to smooth and channeled plains along Hellas' east rim, which may be related to flooding from Reull Vallis and/or accumulation of atmospheric volatiles due to circulation patterns off of the south pole. Comparisons of the geologic evolution of highland terrains around the Hellas perimeter should yield important constraints on past climate regimes.
DE: 5419 Hydrology and fluvial processes
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting