Simulating long-term Noachian landform evolution and paleoclimate

Abstract:

On Mars, the crater degradation processes and rates seem to have changed drastically after the Noachian Period. Relative to the post Noachian craters and impact craters on the Moon and Mercury, Noachian craters generally have distinct cross-sectional profiles, with relatively flat floors and eroded rims. Craters are preserved at various stages of modification, and many larger craters are more heavily degraded than smaller ones. Furthermore, many small Noachian craters (<20–40 km in diameter) have been lost from the surface record, including nearly all Noachian craters <4 km in diameter, while larger ones were degraded to a rimless and shallow form, requiring substantial lateral erosion and infilling. This observation supports that more prolonged erosion is required than can be explained by late, short-lived events at the Noachian-Hesperian (N/H) transition. Longer-term conditions are also more relevant to biological evolutionary timescales than are shorter-term climatic excursions.

We have modeled the evolution of three study sites in the Martian highlands (Noachis Terra, Terra Cimmeria, and Margaritifer Terra near Parana Valles) to constrain the erosional processes and rates that prevailed before the valley networks formed. The purpose of this study is to determine which suite(s) of geomorphic processes and rates best reproduce the relict Noachian landscape and to constrain the long-term Noachian environment through landscape evolution modeling of representative study areas in the Martian highlands.

Our model runs indicate that the rate and pattern of Noachian erosion might have been limited by the weathering rate of the bedrock, if runoff production was high. When the bedrock was set to as readily erodible as regolith, crater rims retreated rapidly, causing the resulting surface topography to be largely obliterated over the model timescale. Also an arid to semiarid climate with a low dependence of runoff upon contributing area best replicates the degree of fluvial dissection and crater degradation in these region.