Age of Martian channels

Abstract

The ages of large martian channels have been studied by determining the relative abundances of craters superimposed on channels and adjacent terrains and by examining superposition relationships between channels and plains and mantle materials. The channels are extremely old, are spatially confined and temporally related to the ancient cratered terrain, and in many cases are related to the as yet poorly understood genetic processes of fretting and chaos formation. No evidence is found for recent channel activity. INTRODUCTIONOf landforms revealed by the Mariner 9 spacecraft during its global reconnaissance of Mars in 1971 and 1972, some of the most dramatic and controversial remain the large, often sinuous channels so reminiscent of terrestrial river channels.In the years since the completion of the Mariner 9 mission, strong differences have developed within the scientific community concerning the mode of channel formation. Low-resolution images foster ambiguous interpretations of morphologic features, often allowing the same channel to be cited as a 'type example' by authors presenting opposed points of view. Unfortunately, higher-resolution photography, when available, often provides as much confusion as clarification. Furthermore, each martian channel has individual characteristics, so that discussions tend to revolve around unique, possibly anomalous, examples. The general categorization scheme developed by Sharp and Malin [1975] will be used to limit the discussion in this paper .to a few specific types of channels. Sharp and Malin [1975] discuss the difficulties in developing a purely nongenetic classification system for martian channels and present a scheme with strong genetic overtones. The channels studied here are those which appear to be formed by the action of external processes on the martian surface, although the considerations of this paper are essentially independent of the mechanism of channel genesis.The focus of this paper is upon the important question of channel age. Initially, it was believed that channels were extremely young because of their fresh appearance and the paucity of superimposed impact craters [cf. Masursky, 1973; Hartmann, 1973]. Early crater counts seemed to indicate ages similar to those of the Tharsis volcanoes and south polar layered deposits, suggesting that Mars had undergone recent geological and, presumably, climatological changes. Estimates of absolute age, based on an impact flux enhanced by as much as a factor of 25 relative to the moon, ranged from tens of millions to hundreds of millions of years. Current interpretation, based on the recognition of more craters and on the reduction of the Mars-to-moon enhancement factor, would increase these ages by an order of magnitude [Soderblom et al., 1974]. This paper draws upon new crater counts and superposition criteria to establish age relationships between martian channels and other surface features. Implications of these relative •Now at ages and a possible absolute time scale are discussed in a separate section. . GENE...

Fluvial Valley Networks on Mars

“…Relative ages of planetary geologic units are determined using superposition relationships and impact crater populations, as surfaces accumulate craters with time (e.g. Malin (1976aMalin ( , 1976b dated the valley networks to the epoch of heavy meteorite bombardment, which declined about 3.85 Ga on the Moon and ∼ 3.7 Ga on Mars, and later workers have confirmed this relative age (Masursky et al, 1977;Pieri, 1980;Carr and Clow, 1981;Baker and Partridge, 1986;Craddock and Maxwell, 1990;Maxwell and Craddock, 1995;Irwin and Howard, 2002;Ansan and Mangold, 2006). 54-64).…”

“…The first papers on Martian fluvial landforms compared the common theatre-headed valley networks to box canyons with headwall springs in the south-western United States and Hawaii (Milton, 1973;Sharp and Malin, 1975;Malin, 1976aMalin, , 1976bPieri, 1976Pieri, , 1980Masursky et al, 1977;Carr and Clow, 1981;Baker, 1982;Mars Channel Working Group, 1983;Laity and Malin, 1985;Kochel and Piper, 1986;Howard et al, 1988). The first papers on Martian fluvial landforms compared the common theatre-headed valley networks to box canyons with headwall springs in the south-western United States and Hawaii (Milton, 1973;Sharp and Malin, 1975;Malin, 1976aMalin, , 1976bPieri, 1976Pieri, , 1980Masursky et al, 1977;Carr and Clow, 1981;Baker, 1982;Mars Channel Working Group, 1983;Laity and Malin, 1985;Kochel and Piper, 1986;Howard et al, 1988).…”

Evidence for Recent Groundwater Seepage and Surface Runoff on Mars

“…However, in 1972 the Mariner 9 orbiter photographed evidence-in the form of giant flood channels and arborescent networks of small valleys-that liquid water (I) might have been stable in the surface environment at some time in the past (2)(3)(4)(5)(6)(7)(8). Analysis of Mars 4 and 5 (1974) and Viking orbiter images (1976-80) contributed to these views (9)(10)(11)(12)(13)(14), as did observations of flood terrain by Mars Pathfinder in 1997 (15-1 7).…”

Origin and development of theater-headed valleys in the Atacama Desert, northern Chile: Morphological analogs to martian valley networks

“…The preservation of ancient cratered terrain in the southern highlands shows that Mars has been hyperarid for about 75% of its history, although it experienced wetter conditions at least intermittently prior to about 3.0-3.6 Ga (e.g., Malin, 1976;Carr and Clow, 1981;Golombek et al, 2006;Fassett and Head, 2008;Grant and Wilson, 2011). The highlands contain fluvially degraded impact craters and branching valley networks, most of which drained to enclosed basins (e.g., Maxwell and Craddock, 1995;Craddock et al, 1997).…”