2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 8:00 AM-6:00 PM

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


SOARE, Richard J., Department of Geography, Environment & Planning, Concordia University, 1455 de Maisonneuve Blvd. W, Montreal, QC H3A 1M8, Canada, PEARCE, Geoffrey D., Dept. of Earth Sciences, Physics & Astronomy, University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada and PAGE, David P., Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom, rsoare@colba.net

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.