Rebuilding the Noachian paleo-surface of Mars

In its past, Mars experienced a warmer and wetter climate than on present days. Many uncertainties remain about the early climate of Mars, for instance on the nature of gas species included in the greenhouse warming or the duration of the warm episodes. Most existing reconstructions of Martian paleo-topography either rely on idealised assumptions, large-scale isostatic corrections, or limited regional reconstructions, and therefore do not explicitly integrate stratigraphic information on buried Noachian terrains. As a result, it is uncertain how paleo-topography impacted the early climate, and the development of the valley network.

For the first time, we present a global reconstruction of the Noachian paleo-surface using constraints from geological mapping, and craters central peaks mineralogy and morphology. Starting from the present-day Mars Orbiter Laser Altimeter topography, we removed all the terrains younger than Noachian, based on the geological map from Tanaka et al., 2014. That includes the large areas from the lowlands in the northern hemisphere, the Tharsis bulge, recent impact basins, craters with inner sedimentary deposits, and the Noachian surfaces extensively affected by post-Noachian tectonic activity such as Valles Marineris and 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 Noachian (lowest layer) and post-Noachian terrains (shallower layer). Phyllosilicates-bearing central peaks and massive morphologies are considered as evidence for excavated Noachian material, while mafic detections without hydrated minerals associated to layers morphologies are interpreted as post-Noachian units. We estimated the stratigraphic uplift for each impact to infer the original depth of the excavation, allowing us to define upper and lower bounds of the Noachian surface. The points are interpolated using a kriging interpolation technique to produce global envelopes, and the Noachian paleo-surface is defined taking the spatial mean of the lower and upper envelopes.

Unlike previous products, this reconstruction directly links surface elevation to independently derived stratigraphic and mineralogical constraints, providing a physically grounded estimate of Noachian topography rather than a purely geometric or isostatic correction of present-day relief. Future refinements of the paleo-surface will include the effects of the true polar wander and lithospheric flexure effects due to the surface loading, particularly for the Tharsis region. This resulting dataset is designed to be used as a common boundary condition for climate, hydrological, erosional, and thermal models. We expect the paleo-surface to allow more realistic simulations of early Mars and a reassessment of the environmental conditions under which valley networks formed.

 

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.