Early thinning, late persistence, diachronous boundaries, and a regional dichotomy in Mars' young sedimentary rocks

Mars' sedimentary rocks record Gyrs of environmental change. New data enable global analyses of paleo-environment relevant physical properties of these rocks, including layer thickness and accumulation rate. Here, using plane-fitting techniques on orbital imagery and elevation models, we find that sedimentary layer thicknesses of post-3.5 Ga rocks across the Martian surface show coherent variations at ~1000 km-scale that are inconsistent with simple volcanic and climatic hypotheses for formation, which are consistent with global compositional homogeneity at orbital scales. These data combined with analyses of outcrop age and total rock volume revealed a global decrease in layer thickness that predates the eventual drop off in preserved sedimentary rock volume per Myr. These constraints confirm a diachronous transition in Mars' global sedimentary rock record while also highlighting a regional dichotomy in young sedimentary rock deposits that has not been quantified before.