Late drainage along portions of Samara Valles, west of Jones Crater, Margaritifer Terra, Mars

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.