Evidence for Global-scale Northern Mid-latitude Glaciation in the Amazo- Nian Period of Mars: Debris-covered Glacier and Valley Glacier Deposits in The

Introduction: Terrestrial cold-based glacial analogs [1,2] have recently been applied to the analysis of fan-shaped deposits on the NW flanks of the Tharsis Montes and Olympus Mons, interpreting them to represent extensive tropical mountain glaciers formed by enhanced snow and ice deposition during periods of high obliquity in the Amazonian [3-8]. Additional Earth glacial analogs have been used to develop criteria for the recognition of glacial deposits in various topographic and environmental settings on Mars [9]. These criteria have recently been applied to the assessment of the fretted terrain, one of the hallmark morphologies of the high-lowland boundary region in the northern mid-latitude Deuteronilus-Protonilus Mensae area (30 o-50 o N and 10 o-75 o E). The fretted terrain [e.g., 10] consists of 1) lobate debris aprons (LDA) that surround many of the massifs and valley walls, and 2) lineated valley fill (LVF) that occurs on the floors of many of the valleys. We addressed the question of whether the accumulation of snow and ice, and resulting glacial activity, could account for some of the observed characteristics of the fretted terrain. In one area (Fig. 1; 1)(~37.5 o N, 24.2 o E) [11] evidence was presented that lineated valley fill formed in multiple accumulation zones in breached craters, alcoves, and tributary valleys and flowed laterally down-valley forming a major trunk system that was characterized by compression of ridges at constrictions, tight folds at converging branches, and a lobate, convex-upward terminus. In a second area (Fig. 1; 2)(~40.5 o N, 34,5 o E) [12] a single integrated system was documented covering ~30,000 km 2 and consisting of multiple, theater-headed, alcove-like accumulation areas, converging patterns of downslope flow into several major valley systems, and broad piedmont-like lobes where the LVF extended out into the adjacent lowlands. The features and deposits in these two areas are interpreted to represent intermontaine valley glacial systems dating from earlier in the Amazonian. Synthesis of criteria for recognition: Using the range of terrestrial analogs and the subset most likely to apply to the recent cold desert environment of Mars [e.g., 1,2,9], the following criteria have been developed to assist in the identification of debris-covered glacial-related terrains on Mars; the interpretation of each is listed in parentheses: 1) alcoves, theater-shaped indentations in valley and massif walls (local snow and ice accumulation zones and sources of rock debris cover), 2) parallel arcu-ate ridges facing outward from these alcoves and extending …