PROGRESS ON GEOLOGIC MAPPING IN THE SOUTHERN UTOPIA BASIN

Utopia Planitia is located within the Martian northern plains and contains a diverse array of pitted cones and domes, whose origin is not well understood. Pitted cones are pervasive in the northern plains, and studies have shown that they indicate something about the past presence and stability of subsurface water on Mars. Studying and mapping the morphology and distribution of these features in various locations can help us better understand the water-based geologic processes in the Martian lowlands. The goal of this map is to document the morphology of pitted cones in southwestern Utopia Planitia and how they might relate to the history of the Utopia basin. We chose to map our study area at 1:150k-scale because 1) the cone features in this area are small (average area of mapped cone features is ~0.5 km²) and a larger area would not provide enough detail for these features and the local contact relationships, and 2) the cones in the northern plains have not been mapped at this scale before. Contact placement, unit definitions, and type localities were all completed on a Context Camera (CTX) controlled basemap supplemented with a Mars Orbiter Laser Altimeter (MOLA) Digital Elevation Model (DEM) and hillshade. We separated the geologic units of this map into four categories: craters, plains, massifs, and cones. The youngest unit is the Amazonian-aged craters. Plains units are the most widely occurring in the area, covering a combined 95% of the map, highly contrasting with the oldest unit – Amazonian-Hesperian-aged massifs that outcrop only seven times and have an average area of 9 km². We interpreted that this massif unit, Htn_f, and the largest plains unit, Alu₂, are the same units identified and mapped in the Nepenthes region, so the unit colors and names have been used in our map for continuity across the lowlands (unit Alu₂ in this map is the equivalent of unit AHlu₂ in SIM 3389). We mapped ~900 cones and separated them into three units based on size, shape, and unit relationships. Though previous studies have mapped pitted cones in Utopia Planitia, only one other publication has investigated these features at a similar scale, and only two cone morphologies were identified in their study area. Mapping pitted cones in Utopia can help resolve how they may have formed and how they relate to the formation of parts of the Martian northern plains.