Geology of the Reull Vallis Region, Mars

Abstract

The geology and stratigraphy of the Reull Vallis region (27.5–47.5°S, 245–270°W) of the southern highlands of Mars are documented through geomorphic analyses and geologic mapping at 1:2,000,000 scale. Crater size–frequency distributions are used to constrain relative ages of geologic units 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 highlands are also evaluated. Rugged highland terrains were formed by repeated impact events and were extensively degraded and embayed by a series of plains. Highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region. Reull Vallis originates in Hesperia Planum, and dissects units of various types and ages. Truncated and bisected wrinkle ridges in Hesperia Planum indicate that the formation of Reull Vallis postdates ridge formation. The morphology of Reull Vallis suggests it had a long and complex history, including subsurface and surface movement of fluids followed by extensive modification by mass wasting. Volcanic and sedimentary plains units in the region record evidence of erosion by surface flow possibly related to development of Reull Vallis. Features produced by mass wasting, such as debris aprons and crater fill material, and aeolian processes appear to form the youngest deposits exposed in the region.