Paleoenvironmental constraints from quantitative sedimentology and geomorphology: Canyon erosion and sand-ripple formation on Earth and Mars
Séminaires Planétologie et Sciences Spatiales
522, bât. Lamarck
Over the past few decades, orbiters, landers, and rovers have significantly expanded our understanding of Mars’ hydrology and climate; however, significant knowledge gaps stand in the way of our quest for early martian life. In particular, the global drying of the planet remains one of the grandest unsolved mysteries in planetary science. To help unravel this puzzle, we develop new quantitative theories for sedimentary processes with implications for both Earth and Mars.First, we focus on the erosion of bedrock canyons by water on Earth and Mars. After showing that groundwater-fed springs may only carve canyons in restricted conditions, we develop new hydraulic theory for flow focusing upstream of horseshoe- shaped waterfalls and combine it with waterfall-erosion mechanics to constrain the discharge, duration, and volume of canyon-carving floods on Earth and Mars. We show that martian canyons at Echus Chasma were carved by large but short-lived floods, not springs. Second, we investigate fluid and sediment controls on the equilibrium size of bedforms. We develop a comprehensive scaling relation to predict the size of ripples forming in various sedimentary environments, including martian brines and methane flows on Titan, and show that the scaling relation predicts the size of large wind ripples forming under a thin martian atmosphere. This new theory, combined with observations of large-ripple cross-strata in wind-blown sandstones of the Burns formation at Victoria crater, suggests that Mars had a thin atmosphere around the Noachian-Hesperian boundary. Collectively, these results provide new mechanistic and quantitative constraints on the past hydrology and climate of Mars that are key to assess Mars’ astrobiological potential through time.