Geologic History of Deuteronilus Cavus in the Ismenius Lacus Region, Mars

The Ismenius Lacus region of Mars has a diverse geological history, and we present the first high-resolution map of the ~120 km Deuteronilus Cavus (36.2°N; 14.0°E, irregular or circular depression) in the fretted terrain south of the dichotomy boundary. Strong evidence suggests a volcanic origin of the regional plains, based on the ~50 m thick volcanic bed underlying 180-300 m of sublimation residue associated with Amazonian plateau glaciation. Pervasive external volcanic flooding, internal erosional modification, and enlargement of a pre-existing crater by up to 175-200% resulted in the cavus' present shape. The phyllosilicates detected within Deuteronilus Cavus could be primary materials associated with surficial aqueous activity, subsurface alteration products excavated by impacts, or a combination of both. We observe branching fluvial channels that are more recent than the traditional valley networks and may be related to fretted terrain resurfacing during the waning period of a high-obliquity glaciation phase. This is consistent with our interpretation of the ~600 m thick lobate and lineated deposits, which are remnants of receding glaciers. The glacial ice, protected by a 15-20 m insulating layer of debris cover, is of significant interest for future landing missions because of its potential to preserve biological and climatological signatures, provide a critical test of Amazonian plateau glaciation, and can be used for in situ resource utilization. With our detailed geological mapping, we improved our understanding of the geological evolution and climatic conditions in the enigmatic fretted terrain near the dichotomy boundary.