Mounds of the Hypanis fan system, Mars: sedimentary vs magmatic volcanism

The presence of sedimentary volcanism on the surface of Mars is still debated, due to the limitations imposed by studying Martian proposed mud volcanoes only with remote sensing techniques (without the so called “ground truth”) and the issues related to “equifinality” (different geological processes may produce similar morphologies on planetary surfaces). Being able to confirm the active role of sedimentary volcanoes on Mars would be extremely important [1]: they can probe the subterranean environmental conditions of Mars, more suitable for biological activity than the hostile surface, and can represent important “windows” into the deep sediments underneath the crust. This research is a detailed geological investigation on the area of Hypanis Vallis fan-delta system, proposed as a reference site for the “Rosalind Franklin” rover landing site (Oxia Planum), [2] with the purpose to constrain the stratigraphic relationships between the “mounds” (positive-relief features reported in the surrounding of the sedimentary body) and the geologic units of the study area, to characterize and classify these edifices using morphological and morphometrical parameters, and finally infer their genetic origins. Hypanis mounds were previously studied by other authors, who proposed for them the hypothesis of erosional remnants of a previous contiguous surface [3] and the possibility to be the results of “constructive” sedimentary and volcanic processes, or eroded basement material [4]. Our findings seem to support well two alternative explanations: sedimentary and/or phreatomagmatic volcanoes. Hypanis mounds geomorphological features and sizes are comparable with supposed Martian sedimentary volcanoes and scoria/rootless cones, and also with terrestrial analogues. The geological map that summarizes the main sedimentary events at the Hypanis Vallis outlet region shows a setting that may have been suitable for the development of both the volcanic processes. Moreover, the possibility of sedimentary and phreatomagmatic eruptions around the big sedimentary body of Hypanis could provide to this area an elevated geological and astrobiological potential.