Abstract:
Relatively pristine valley segments along medial-to-distal Samara Valles in Margaritifer Terra likely originate within the continuous ejecta west of the Late-Hesperian Jones impact crater. Valley expression between a ~ 46 km3 upper basin and a ~ 7 km3 lower basin is typically well-incised with smooth walls and a relatively uniform width-to-depth, but elsewhere varies from well-incised to diffuse and some segments appear anastomosing or truncate one another. Many are more than a kilometer across and 100 s of meters deep and display interior terraces and depositional forms. More pristine segments continue north and are associated with finely layered, alternating dark- and light-toned deposits well beyond Jones ejecta. Basins are approximately bound by the -1275 m MOLA contour and the upper basin displays benches and partially filled craters near and below that elevation. Lower interior surfaces of the upper basin are not incised, expose relatively light-toned discontinuous deposits, include polygonal fractures, and are locally Mg/Fe phyllosilicate-bearing. We interpret the formation of the relatively pristine segments as the result of water from impact-melted ice in and under the Jones ejecta draining westward, with some filling the upper basin. Water accumulated over a period of months to years before overtopping the divide and draining at rates perhaps on order of 104 m3s-1 before filling and overwhelming the lower basin and breaching two additional local divides. Drainage persisted for a period of years at most and then ceased. If correct, our model indicates a geologically brief interval of transient potentially habitable environments relatively late in Mars history that was likely unrelated to global climate.
•Pristine, young valleys incise ejecta of the Late Hesperian Jones crater, Mars.•Pristine valleys are separated by basins, and express interior deposits and terraces.•Valley formation was related to drainage of ice melted during the Jones impact.•Valleys likely formed over a period of months to years and then activity ceased.•Valleys and basins represent transient late, aqueous, likely habitable environments.
