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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 108, NO. E4,
8031,
doi:10.1029/2002JE001900,
2003
Geologic settings of Martian gullies: Implications for their origins
Allan H. Treiman
Lunar and Planetary Institute,
Houston,
Texas,
USA
Abstract
Martian gullies are found on steep slopes of all origins, on all sorts of terrains of all ages, scattered across nearly all
of Mars. Gullies are observed on all manner of substrates (layered, massive, shattered, rubble), with or without nearby mantling
deposits. Gullies are most common in the southern midlatitudes but also occur in the northern hemisphere, in near polar terrain,
on equatorial volcanoes, and on northern plains. Most gullies in the southern hemisphere are on south-facing slopes, but they
occur on slopes of all orientations. Gullies are among the youngest features on Mars but locally are overlain by eolian deposits
and cut by faults. Old or eroded gullies are rare, and those found have been partially stripped from slopes, leaving no rock
debris behind. Most gully deposits contain no detectable rocks. These data are inconsistent with published hypotheses of gully
formation, including seeps and breakouts of water or brine, hydrothermal activity, cryovolcanism, and breakouts from liquid
carbon dioxide. The data are consistent with gullies being dry flows of eolian material (dust and silt), comparable to climax
snow avalanches on Earth. Eolian sedimentation should be correlated little with underlying geology: cause of slope, age of
terrain, type of terrain, or the nature of the rocks. Eolian sedimentation should be correlated with wind deceleration (which
will cause suspended sediment to drop), and areas with common gullies are those with strong wind deceleration (predicted by
global circulation model). In such areas, sediment will be deposited preferentially in the lee of obstacles; for the gully-rich
areas of the southern midlatitudes, winds blow from the NNW, so that sediment is deposited on SSE-facing slopes (i.e., poleward).
These predictions are in accord with observations.
Published 8
March
2003.
Index Terms: 6225 Planetology: Solar System Objects: Mars; 5470 Planetology: Solid Surface Planets: Surface materials and properties; 1824 Hydrology: Geomorphology (1625); 1827 Hydrology: Glaciology (1863).
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Citation: Treiman, A. H.
(2003),
Geologic settings of Martian gullies: Implications for their origins,
J. Geophys. Res.,
108(E4),
8031,
doi:10.1029/2002JE001900.
Copyright 2003 by the American Geophysical Union.
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