Eolian sedimentation on Earth and Mars: Some comparisons

Eolian sediments on Earth are mostly formed from quartz; they consist, in large part, of eolian sand deposits in deserts, silt and loess deposits in and adjoining present and former glaciated areas, and finally clay-sized particles carried in suspension for relatively long distances and deposited in oceanic areas by winds. The quartz particles in these regimes originally came from a granitic source; stresses in granitic rock formation, glacial action, and wind abrasion are largely responsible for making the particles available for the three kinds of eolian deposits. With respect to eolian sediments on Mars, it appears that an entirely different set of criteria must apply, but some critical parameters can usefully be compared. Evidence for free quartz on Mars is lacking and sand-sized particles are probably basaltic, although there does appear to be a deficit in the sand size range. Glacial action does not appear to be available as a large-scale particle producer but high-velocity winds could be efficient producers of very fine particles. Fine particles may aggregate in a similar way to that observed in the Australian regions where “parna” is seen; this could supply a silt mode on Mars. Impact experiments with basalt in eolian abrasion devices suggest that basalt sand-sized particles fragment rapidly to produce silt and clay-sized detritus. Cohesive forces must be more effective on Mars since the gravitational contribution to the bond/weight ratio (R) is lowe; if R = 1 at about 100 μm on Earth, then R = 1 at about 140 μm on Mars and a much greater range of deposits will be stable. Compared to the terrestrial situation, both larger and smaller particles can be expected to make significant contributions to eolian sediments on Mars. The low gravity and the high speed of moving particles and the relatively weak rock material of which they are composed will allow large-scale fine particle production.