Geology of the Reull Vallis region, Mars

The geology and stratigraphy of the Reull Vallis region (27.5-47.5 degreesS , 245-270 degreesW) of the southern highlands of Mars are documented throug h geomorphic analyses and geologic mapping at 1:2,000,000 scale. Crater siz e-frequency distributions are used to constrain relative ages of geologic u nits and determine the timing and duration of the various geologic events. The origin and evolution of the Reull Vallis outflow system and the extent to which Reull Vallis and other fluvial features modified the surrounding h ighlands are also evaluated. Rugged highland terrains were formed by repeat ed impact events and were extensively degraded and embayed by a series of p lains. Highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region. Reull Vallis originat es in Hesperia Planum, and dissects units of various types and ages. Trunca ted and bisected wrinkle ridges in Hesperia Planum indicate that the format ion of Reull Vallis postdates ridge formation. The morphology of Reull Vall is suggests it had a long and complex history, including subsurface and sur face movement of fluids followed by extensive modification by mass wasting. Volcanic and sedimentary plains units in the region record evidence of ero sion by surface flow possibly related to development of Reull Vallis. Featu res produced by mass wasting, such as debris aprons and crater fill materia l, and aeolian processes appear to form the youngest deposits exposed in th e region. (C) 2001 Academic Press.