Reconstructing the Noachian paleo-surface of Mars

Studying Noachian times on Mars from both climate and geological evolution is crucial to characterize the habitable conditions of early terrestrial planets. To understand global planet dynamics in its earliest times, assessment of the ancient topography of Mars is required. However, current paleo-topography models are mostly based on idealized assumptions, large-scale isostatic corrections, or limited regional reconstructions, and do not rely on geological analyses to integrate stratigraphic information from buried Noachian terrains. Therefore, the impact of paleo-topography on the early climate and the formation of valley network remains poorly constrained.

For the first time, we present a global reconstruction of the Noachian paleo-surface using constraints from geological mapping (Tanaka et al., 2014), and craters central peaks mineralogy and morphology. First, we removed all the post-Noachian terrains from the Mars Obriter Laser Altimeter topography, including the lowlands from the north hemisphere, the Tharsis province, and post-Noachian impact craters with their inner sedimentary deposits. We also excluded Noachian surfaces extensively reworked by younger tectonic or volcanic events, like Valles Marineris, and the outflow channels.

We used the mineral detections in the central peaks of impact craters and the central peak morphologies to describe the buried terrains and find the boundary between lowest Noachian terrains and shallower post-Noachian deposits. We interpret phyllosilicates detections and massive morphologies as part of the Noachian excavated material, and mafic detections without hydrated minerals associated to layering as post-Noachian samples. By inferring the stratigraphic uplift for each Noachian impact, we provided constraints on the upper and lower bounds of the Noachian surface. The points are interpolated using spherical harmonics to produce smooth global envelopes, and the Noachian paleo-surface is defined by the spatial mean located between the lower and upper envelopes. We accounted for True Polar Wander caused by the formation of the Tharsis bulge, and included isostatic corrections.

Unlike previous products, the reconstructed Noachian paleo-surface links the surface with stratigraphic and mineralogical constraints. This provides a physically grounded estimate of Noachian topography rather than pure corrections of the current topography. Future work will bring new improvements by including the effect of the lithospheric flexure due to the surface loading. The final dataset is designed to be used as an input for modelling climate, hydrology, bathymetry, and landscape evolution through time. We expect our Noachian paleo-surface to allow even more realistic models of early Mars, and a robust reassessment of the environmental conditions during the formation of valley networks.

Tanaka, K. L. et al. (2014). The digital global geologic map of Mars: Chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history. Planetary and Space Science, 95, 11-24.