Treatises on the paleohydrology of Mars and Earth

Abstract

A paleotopographic reconstruction has revealed the potential existence of an ancient enormous drainage basin and productive regional aquifer system in the eastern part of the Tharsis region. The basin model addresses a fundamental question in martian paleohydrology: Where did the massive amount of water required to carve the catastrophic outflow channels come from? These gigantic channels are typified in the recently discovered northwestern slope valleys (NSVs). The paleohydrologic implications for the NSVs are enormous, as they represent: (1) previously undocumented Noachian and early Hesperian martian catastrophic floods, (2) a watershed to the northwest of Tharsis, possibly related to the early development of the circum-Chryse system of outflow channels, a watershed to the northeast that records flooding as recent as the early Amazonian, and (3) a potential source of water for a northern plains ocean and/or paleolakes. In addition to catastrophic outflows, Hesperian and Amazonian hydrological activity resulted in the formation of sapping valleys, such as Abus Vallis. An investigation of Wet Beaver Creek, Arizona, revealed geological, hydrogeological, and geomorphic similarities between Wet Beaver Creek and Abus Vallis, Mars. As such, one may infer lithological and hydrological similarities as well. Wet Beaver Creek represents geological and climatological conditions that result in rapid, sometimes dynamic, formation of sapping channels. Sapping channels that occur along the highland-lowland boundary scarp, such as Abus Vallis, may now also be explained in terms of rapid formation during short-term periods of global climatic change, as well as by hypersaline aquifers and hydrothermal processes. The dark slope streaks on Mars may represent yet another type of hydrogeomorphic process, different from the NSVs and Abus Vallis. In light of Mars Global Surveyor-based geographic, geologic, and morphologic considerations, spring discharge is a viable explanation for the formation of dark slope streaks. Such activity would indicate the existence of near-surface aquifers and, more importantly, hydrological processes acting upon the surface of the planet, making it the only other hydrogeomorphically-active planet in the solar system besides Earth.