Ice Content of Mantling Materials in Deuteronilus Mensae, Mars

Layers of ice and dust (i.e., “mantle”) are found throughout the mid-latitudes of Mars, where they drape and mute topography and record the recent climate history. Many of the youngest Late Amazonian “latitude-dependent mantles” have been characterized, but the full range of mantle characteristics, including variations in ice content and age, has not been well documented. To advance our understanding of these ice-dust units, we use SHAllow RADar (SHARAD) radar sounding data to constrain the subsurface physical properties of a widespread Middle Amazonian mantle unit within Deuteronilus Mensae. This region hosts a high density of glacial landforms, which allows assessment of the stratigraphic relationship between mantle deposits and glacial ice. SHARAD reflectors at the base of the mantle units are used to determine moderate dielectric constants (∼5.75) and high loss tangents (∼0.038). These radar properties imply relatively limited ice content and high-loss mantling materials with possible enhanced roughness or subsurface scattering. Further, we interpret deeper reflectors that are continuous with glacier basal reflectors and that suggest materials with lower dielectric constants (∼3.2–4.5) and loss tangents (0.0071–0.0120) to be due to extensions of stagnant, possibly lithic-rich, glacier ice that are buried by a mantle layer. This study demonstrates the high variability in the origins and evolution of mid-latitude mantling units on Mars. While the most recent latitude-dependent mantling deposits may still be ice-rich, older deposits, such as those preserved in Deuteronilus Mensae and elsewhere in the mid-latitudes of Mars, may be largely desiccated or contain a more heterogeneous and limited distribution of ice.