HR: 0800h
AN: P31C-0546    [Abstracts]
TI: Gully-Polygon Interactions, Stratigraphy, and Distribution on Earth and Mars: Thermal Contraction Crack Polygons as Part of Cold-Desert, Near-Surface, Fluvial Systems
AU: * Levy, J S
EM: joseph_levy@brown.edu
AF: Brown University, 324 Brook Street Geological Sciences Box 1846, Providence, RI 02912, United States
AB: The distribution and structure of thermal contraction crack polygons in the South Fork region of Wright Valley are examined in order to document the manner in which patterned ground contributes to the flow of water in cold desert gully systems. Thermal contraction crack polygons span the interface between the atmospheric, permafrost, and hydrological systems in Wright Valley, providing a unique window into the interactions between these agents of geomorphic change. We find that polygonally patterned ground contributes to the generation, transport, and storage of water in the Wright Valley gully systems. Generation is contributed to by the trapping of windblown snow in gully troughs; transport, by changes to the ice-cement table and active layer hydrological properties caused by polygon trough formation; and storage by sorting of colluvium within polygons by grain-size. Further, we find that the styles of patterned ground can serve as an indicator of the degree of fluvial modification of a surface, ranging from nearly unmodified sand-wedge polygons to polygons forming within inactive gully channels. Finally, we find that thermal contraction crack polygons can be used as a stratigraphic element for evaluating the formation sequence of landscape elements. Cross-cutting relationships between gully channels and polygons suggest that gully channels formed in a polygonally patterned surface. Gully fan deposits overprint patterned ground, and are dissected by patterned ground that forms a continuous network across the fan surface contact, suggesting that patterned ground evolution "kept pace" with gully fan aggradation. Taken together, these lines of evidence suggest the continuous presence of permafrost beneath the Wright Valley gullies during the entire period of gully emplacement. These observations provide a baseline for interpreting patterned ground observed on gullied terrains on Mars. Similar relationships between gully alcoves, channels, and fans and patterned ground suggest that many martian gullies formed on patterned surfaces, implying that these gullies may form from the melting of trapped frost and snow under appropriate microclimate conditions.
DE: 0702 Permafrost (0475)
DE: 1825 Geomorphology: fluvial (1625)
DE: 5419 Hydrology and fluvial processes
DE: 6225 Mars
DE: 9310 Antarctica (4207)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting