Long‐term precipitation and late‐stage valley network formation: Landform simulations of Parana Basin, Mars

Abstract

[1] We use a computer landform evolution model to show that Noachian-Hesperian-aged, late-stage valley network formation required numerous and repeated moderate flood events rather than one or a few continuous, multiyear, deluge-style flows. We introduce a technique that generates an estimated ''initial conditions'' digital elevation model (DEM) of the Parana Valles drainage catchment (PDC) prior to valley network incision. We then explored how variations in three classes of environmental parameters related to fluvial processes, and surface material properties evolve the initial conditions DEM. Specifically, we parameterized discharge scaling, evaporation from ponded water, and the effects of an indurated surface crust. Each simulation run produced a model output DEM that was qualitatively and statistically compared to the actual surface DEM. Simulations with an arid to semiarid climate, moderate evaporation rates, and an indurated surface crust provide the best match to the actual surface. Simulated valley network formation requires periods of fluvial activity that last a minimum of 10 3 -10 4 years under constant delugestyle conditions. However, craters within the PDC in deluge-style simulations overflow and generate exit breaches that cut through all crater walls. Longer simulations (10 5 -10 6 years) that modeled repeated, episodic flows with interim evaporation avoid universal crater breaching. The paucity of crater rim exit breaches in the PDC and the southern highlands in general implies both that the precipitation was not continuous and that formation conditions were inconsistent with a few short-lived extreme climate excursions such as might be induced by large-scale impacts or other cataclysmic events.

Juvenile chemical sediments and the long term persistence of water at the surface of Mars

“…The observation that these precipitates have persisted to the present further suggests that they have seen little liquid water since they formed. This conclusion is consistent with recent studies of (Stepinski and Stepinski, 2005;Fassett and Head, 2008a;Fassett and Head, 2008b;Barnhart et al, 2009;Som et al, 2009). …”

“…They also suggest that some features, such as catastrophic outflow channels, could be the result of repeated short-duration episodes of aqueous activity. Another study on the origin of valley networks in the Parana Basin requires an arid to semiarid climate that lasted for a minimum of 10 3 -10 4 years (Barnhart et al, 2009). The authors stress the importance of episodic precipitation events that must have been punctuated by periods of evaporation to produce the observed morphologies.…”

“…Modeling studies exploring the nature of Noachian valley networks agree that an arid climate is required to reproduce the observed drainage characteristics -a wetter climate invariably produces features inconsistent with observed topographic distributions and branching patterns and causes breaching of craters where water could have ponded (Stepinski and Stepinski, 2005;Barnhart et al, 2009;Som et al, 2009) Stepinski (2005) argue that the closest Earth analogs come from the Atacama Desert, a region with negligible annually averaged precipitation. They also suggest that some features, such as catastrophic outflow channels, could be the result of repeated short-duration episodes of aqueous activity.…”

Characterization of fluvial activity in Parana Valles using different age-dating techniques

“…Parana Valles is located between Margaritifer and Noachis Terra in a large basin that also includes Loire Valles and Erythraeum Chaos (Barnhart et al, 2009). Parana Valles was chosen as a site for evaluating the different age-dating techniques because of the good coverage high-resolution imagery and the high density of valleys.…”

“…We applied three distinct techniques to obtain the age of Parana Valles (Fig. 1), located between Margaritifer and Noachis Terra in a large basin that also includes Loire Valles and Erythraeum Chaos (Barnhart et al, 2009). This area was chosen because of the availability of high-resolution imagery and because it contains a relatively high density of valley networks.…”