Glacial Landsystems on Mars: Integrating Landform Assemblages, Glaciations, and Cli- Mate Cycles

Introduction: The strong geomorphic similarities between lobate deposits 1) on the northwest flank of the Tharsis Montes [1,2] and 2) along the dichotomy boundary between 30° and 50° [3] with terrestrial cold-based glaciers and glacial deposits has led to hypotheses for geologically recent (Amazonian-age) low and mid-latitude glaciation on Mars [1,4]. The key to these studies has been to identify individual landscape elements on Mars and to match them with terrestrial counterparts [5,6]. Building on this work [1-6], the next logical step is to integrate a landsystems approach, whereby assemblages of landforms over wide spatial scales may be used to deconvolve the evolution and maturation of glacial cycles on Mars. As a starting point, we examine here the areal distribution of glacial deposits on the NW flank of Arsia Mons and then compare these features to terrestrial counterparts that formed during the build up, maturation (glacial overriding of mountain topography), and ultimate sublimation of Miocene-age cold-based glaciers in the Antarctic Dry Valleys (ADV) [7]. Tharsis Montes glacial facies (Arsia Mons): The Amazonian aged deposit covering ~180,000 km 2 of the western flank of Arsia Mons displays several features diagnostic of deposition from cold-based ice (details are outlined in [1]). Foremost are: 1) a ridged facies, which is an outermost zone of over 100 arcuate and parallel raised ridges (drop moraines), each up to 10 meters high and 100 km long; 2) a knobby facies that represents a medial zone of rough, hummocky topography (sublimation till) superposed on intact lava flows; and, 3) a smooth facies, interpreted as debris-covered glaciers, which occurs in a proximal zone abutting the upper flanks of Arsia and consists of several individual lobes and superposed parallel raised ridges. Drop Moraines: Drop moraines are produced as englacial and/or supraglacial debris is dropped at stationary ice margins. Moraine size reflects the debris content in the ice and the duration of ice-front stabilization. Arsia drop moraines are characterized by lateral continuity over hundreds of km, even spacing in plan view (similar to grooves on a record), and repetitive morphology. The continuity of drop moraines at Arsia requires homogeneous and widespread englacial and/or supraglacial debris. Such homogeneity is only achieved with atmosphere-related transport and deposition of dust and/or pyroclastic material onto the ice surface. Extensive aeolian modification of drop moraines observed in MOC images indicates that the grains comprising these features are highly susceptible to wind erosion. The uniform spacing …