Will McMahon (University of Cambridge)
Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6–3.0 Ga. Despite widespread geomorphic evidence, few analyses of Mars’ alluvial sedimentary-stratigraphic record exist, with detailed studies of alluvium largely limited to smaller sand-bodies amenable to study in-situ by rovers. The work discussed in this talk, completed whilst at Utrecht University, discusses a far larger, 1500-m-wide, 190-m-thick sedimentary succession identified from satellite imagery and located in the NW Hellas Basin. Models for siliciclastic deposition are largely based on sedimentary environments on Earth, where physical form and process is near ubiquitously influenced by biology in some way. To eliminate the influence of biology here, the interpretations of the sedimentary architecture at Hellas stem from tangible observations made from Earth’s Precambrian (pre- vegetation) record. The deposits mirror partial terrestrial analogues subject to low-peak discharge variation, implying that river deposition at Hellas was subject to semi-perennial, or even perennial, fluvial flow. Furthermore, conceptual advances in our understanding of how time is preserved at outcrop suggest active water-conduits may have been maintained for 100,000 years or longer. These results strongly suggest a precipitation-driven hydrological cycle was operational on Mars by the mid-Noachian, a finding only made possible through careful analogy with sedimentary rocks deposited on Earth in the absence of complex life.
About the author
William’s research currently integrates techniques in sedimentology, geochemistry and petrology to study some of Earth’s most fundamental transitions, such as the initial emergence of metazoans and subsequent terrestrialization of the continents. He also enjoys working in planetary geology and have focused projects aiming to demonstrate how, through biological evolution, Earth’s sedimentary-stratigraphic record has become differentiated from those on other planets.