VALLEY NETWORK PRESERVATION IN OXIA PALUS, MARS

Valley networks on Mars are typically mapped as negative relief features. However, burial and erosion have altered the form of some valley networks, resulting in forms that range from aligned pits, to knobs and ridges in cases of landscape inversion. Because these variations in valley network preservation state are now recognized, a more complete record of the history of water on Mars can be cataloged. We mapped the spatial distribution of these specific morphologic variations of valley networks to compare with existing valley network maps. The GIS database was created with ConTeXt (CTX; ~6 m/px) camera images, supplemented with THEMIS infrared (100 m/px) images. Efforts to date have focused on the Oxia Palus quadrangle (Mars Chart 11) located between 0 to 30 degrees north latitude, and 0 to 45 degrees west longitude.

Over 2500 km of new valley network segments were identified, half of which are ridge forms (often termed sinuous ridges). Branching ridge networks are interpreted as inverted channels, particularly where there is continuity with negative-relief channels. Many of the networks transition between different forms along route. For example a system may include aligned pits, ridge segments and channel sections. The preservation state of the valley network is a combined result of the material properties for both channel fill deposits and the substrate over which water originally flowed, as well as the subsequent history of deposition and erosion at any given site. Variations in form within the same valley network reflect heterogeneity within the system and a complex formation history.

The majority of the mapped features are located in western Arabia Terra and northwestern Sinus Meridiani on terrain that is devoid of valley networks in prior maps. This discrepancy is due in part to the higher resolution images examined in this study. Preliminary analysis shows these newly identified fluvial landforms vary in their stratigraphic position. In addition, certain preservation states correlate with specific geologic units. For example, all of the branching networks with aligned pits are found in a small region (<12,000 km²) of the scarp-forming unit. These new results imply that Mars had multiple periods of fluvial activity in the Noachian.