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 Deuteronilus Cavus (36.2°N; 14.0°E, ∼120 km diameter) 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 the 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, to provide a critical test of Amazonian plateau glaciation, and to 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. Plain Language Summary: The ∼120 km long Deuteronilus Cavus was initiated by an impact event. The resulting impact crater was modified by glacial erosional and fluvial processes, leading to the enlargement of 175%–200% of the pre‐existing crater. In addition, we find strong evidence for recent glaciation (<1 Ga) that left 180–300 m of sublimation residue on the plateau superimposed on a ∼50 m thick volcanic bed, suggesting a volcanic origin of the regional plains. During the waning period of a high‐glacial phase, the meltwater ponded on the surface of the cavus, altered surface rocks to produce phyllosilicates, formed channels (now observed as inverted sinuous ridges), and locally distributed branched fluvial channels that are more recent than the traditional valley networks. Glacial landforms still contain up to 600 m of remnant ice from the retreating glaciers at the end of the last glacial period. The relatively pure ice, protected by a 15–20 m insulating layer of debris cover, is critical for future landing missions because of its potential to preserve biological and climatological signatures and to be used for in situ resource utilization. Overall, this research enhances our understanding of the geological evolution and climatic history of Mars. Key Points: We have produced the first high‐resolution map of Deuteronilus Cavus in the fretted terrain south of the Martian dichotomy boundaryThe region records a complex erosional and depositional history, including fluvial and glacial processes in the Amazonian periodThis study provides a framework for exploration of high‐obliquity mid‐latitude plateau glaciation [ABSTRACT FROM AUTHOR]