Constraints on the uncertainty, timing, and magnitude of potential Mars oceans from topographic deformation models

Abstract

Proposed ocean paleoshorelines on Mars have faced criticism over their genetic interpretation and because they deviate significantly from an expected equipotential surface (by many kilometers). Multiple geophysical deformation models have been proposed to explain this large topographic range and deviation including true polar wander and direct Tharsis-induced deformation. Yet, the application of these models is potentially flawed as there exists no consensus on exactly where these proposed paleoshorelines are located. Here, we apply these models to proposed maps and mappings of the putative martian ocean shorelines and show that even when considering deformation due to the rise of Tharsis and its associated true polar wander, the observed deviation within each Arabia level's paleotopography precludes them as past equipotential surfaces. Additionally, we compute best-fit ages for all proposed paleoshorelines relative to the rise of Tharsis and the ages span nearly the entire period of Tharsis construction. Assessment of the paleoelevations of open basin deltas and valley network termini also suggests disagreement with the timing of such features with a paleoocean. Overall, we find that these geophysical deformation models are unable to explain the large elevation ranges observed in the putative shoreline data and that the long-wavelength trends may simply be the result of mismapped features along the topographic dichotomy which itself may have been modified by Tharsis and/or true polar wander.