Aeolian Environment Research Articles

Differential aeolian redistribution rates on Mars

THE surface of Mars gives abundant evidence for aeolian activity, including wind-laid dust and ice deposits at the poles that may be several kilometres thick, a vast dune field surrounding the north polar deposits, a dust mantle of varying thickness covering the high to mid-latitudes, and both depositional and deflationary aeolian landforms in the equatorial latitudes. Two major questions concerned with the martian aeolian activity are: first, what are the rates of erosion and redistribution of surface materials such as rock and soil deposits; and second, are most of the large-scale aeolian features seen on Mars products of the present aeolian environment, extrapolated back through geological time, or were most of the features produced in a different climatic regime? Presumably, a different climatic regime, either associated with an early, denser atmosphere, or with periodic variations in atmospheric conditions induced by obliquity changes, would strongly modulate the vigour of aeolian activity1. The Viking Orbiters and Landers, which began acquiring data during the summer of 1976, have now monitored the aeolian environment for slightly more than one full Mars year. Data acquired during the mission have enabled us to investigate these questions for aeolian effects averaged over billions of years, tens of thousands of years, and during a single year.

Dome-shaped aeolian dunes in the frodsham member of the so-called “keuper” sandstone formation (scythian-anisian: triassic) at Frodsham, Cheshire (England)

At four localities near Frodsham, especially in the railway cutting, a wellsorted mottled soft fine-grained sandstone lithofacies lies above a cyclic fluvial pebbly red sandstone lithofacies. It is suggested that the former facies is aeolian, and comparison with the internal structures of present-day aeolian dunes in the White Sands Desert, New Mexico, enables features of dome-shaped and, to some extent transverse, dunes to be recognized. The aeolian environment is interpreted in detail in terms of local derivation of abundant sand from upwind parts of a dunefield in which dried-out river courses were winnowed by moderate breezes where transverse dune structures are initiated, rising to strong breezes and moderate gales where dome-shaped types arise. These palaeowinds were directed unidirectionally from an easterly point in low latitudes north of the palaeo-equator. In the exposures available, cross winds were most commonly directed from the south. It is suggested that the term Frodsham Facies be restricted in future to define deposits of aeolian environments where dome-shaped dunes are dominant.