Late Hesperian to early Amazonian midlatitude Martian valleys: Evidence from Newton and Gorgonum basins

Abstract

[1] Numerous shallowly incised valleys extend from the upper interior rims of Newton and Gorgonum basins across smooth interior basin deposits. These valleys are a few meters to 300 m wide and may have experienced discharges over all or most of their width, implying that they are, in fact, incised channels. In Newton Crater these valleys extend up to 75 km, to near the center of the basin floor. In Gorgonum basin the valleys terminate at what we interpret to be a former ice-covered lake. These valleys appear to be examples of scattered, shallowly incised valleys found throughout the midlatitudes of Mars superimposed upon the widespread mantling deposits within the region. On the basis of crater count age dating, the interior valleys in Newton and Gorgonum basins were formed at about the Hesperian to Amazonian transition. The runoff through the valleys may have occurred due to episodic melting of snow and ice that had accumulated on the crater rims. Temperatures warm enough to cause extensive melting may have occurred during optimal orbital and obliquity configurations because of intensive volcanism releasing greenhouse gasses or as a result of a brief episode of warming from a large impact somewhere on Mars. The valleys were formed at about the same time as major outflow channels were active along the highlands-lowlands boundary. Water delivered to the northern lowlands by the outflow channels may have been recycled as snow and ice deposits within the Martian midlatitudes. The episodic melting of such deposits may have formed the midlatitude valleys.