Evidence of Very Recent, Very Late Amazonian Periglacial & Glacial Processes in Utopia and Northwest Elysium Planitiae, Mars

Recent Mars climate-change models show that obliquity-driven atmospheric transportation could have delivered substantial volumes of dusty H2O-snow to the middle-latitudes of Utopia and western Elysium Planitiae in the late Amazonian period. Using terrestrial cold-climate landscapes as geological analogues, we have identified two landscape-types in the Planitiae whose members (by dint of their morphology, features, scale and possible origin) are consistent with atmospheric deposition and modification by periglacial (~44-54°N) or glacial processes (~31-46°N). The periglacial landscape comprises: 1. lobate, sometimes scalloped-depressions (reminiscent of drained thermokarst-lakes); 2. polygonal patterned-ground (that could have been or may still be underlain by ice-wedges), 3. near-rim, crater-wall gullies (the possible product of highly localised ground-ice thaw); and, 4. polygon-juncture pits (where water/ice could have collected and evaporated/sublimated). On Earth, this type of landscape marks ice-rich ground mobilised by oscillations of mean temperatures around 0°C. Our previous work suggested that two characteristics of the depressions - internal terraces and orthogonal polygons - could be the work of ponded water and its subsequent loss by evaporation or drainage. Agewise, some depressions might be extremely young, cross-cutting/superposing a number of crater-wall gullies. Moreover, many of the gullies and superposed depressions occur in the Astapes Colles Unit (ACU), one of the youngest units in region. The glacial landscape is intra-crater and comprises fill material, previously associated with late Hesperian/early Amazonian circum-Chryse discharges. We present an assemblage of images highlighting the possibly recent degradation (or thaw) of this fill in medium-sized (~7-20 km in diam.) ACU craters. At the same time, we point to some intra-crater mounds in small-sized craters (~1-3 km in diam.) whose characteristics, much like those of the periglacial landscape identified above, point to an obliquity-driven origin and the localised occurrence of ponded water in the late Amazonian period.