Polythermal Glacial Landforms in Acidalia Planitia Reveal Amazonian Ice-Related Processes on Mars

Bonestell Crater in Acidalia Planitia and a ∼13 km-diameter crater to the northwest preserve geomorphic and thermophysical evidence of Amazonian-aged glacial activity. In Bonestell, lobate deposits along the northwestern rim and a cirque-like depression along the southeastern rim display steep scarps, lineated textures, and polygonal surface patterns consistent with debris-covered ice and periglacial modification. The cirque depression contains thrust-like ridges and compressional structures resembling terrestrial glacial cirques, interpreted as a remnant of polythermal glaciation, where cold- and warm-based ice likely coexisted. Thermal inertia values across these deposits range from ∼300 to 800 J·M⁻² K⁻¹·s^−1/2, suggesting a downslope transition from poorly consolidated sediment to indurated material. CRISM spectra reveal hydrated minerals and altered silicates consistent with episodic basal melting or volatile-driven alteration. In contrast, the unnamed northwest crater hosts clear examples of rock glaciers. Multiple lobate flows descend from alcoves along the crater walls, exhibiting convex-upward profiles, degraded termini, and compressive ridges that closely resemble terrestrial debris-covered glaciers. HiRISE image data show flow-parallel lineations and banding indicative of internal deformation and sublimation-driven modification. Spectral unmixing of THEMIS ROTO data acquired from multiple viewing geometries fit modeled mixtures of sand and indurated crust with thermal inertia values ∼600 J·M⁻² K⁻¹·s^−1/2, consistent with debris-coated ice. These results demonstrate that mid-latitude ice in the region is preserved in diverse forms, including cirques, rock glaciers, and debris-mantled ice masses. Their co-occurrence indicates that Amazonian glaciation was not singular nor isolated but regionally extensive and capable of producing transient wet-based conditions that locally sustained liquid water and habitable environments.