Hi robert, re post 56.
Thanks for the links.
The first is a fantasy site and therefore not germane to the issue. The second distinguishes between silt sized deposits of loess and sand sized dune deposits. The third does not make clear the nature and context of the "silt dunes". The fourth link shows how source bordering "silt dunes" of the Missouri river are made. In such cases the silt is deflated, transported and deposited as sand-sized aggregates, even if that link does not make it clear. The fifth link is in error when it talks about "silt dunes" as loess deposits, to which the page links "silt dunes", whether in the US or China, do not form dunes but topography-mantling blankets. The sixth link does not contain any reference to dunes at all that I can find. Neither does the seventh, which simply talks about aeolian silt burying topography.
It is important to recognise that "silt dunes" is often used as a kind of shorthand jargon. The term "clay dune" is been similarly been used elsewhere. Unfortunately is rather sloppy. It is worse when semi-popular or non-scientific articles refer to any mound of wind deposited material as a "dune" when in many cases they are not.
To the best of my knowledge silt-sized material, entrianed, transported, and deposited as such, does not form dunes, although they do form other deposits. Dunes require sand sized grains. But I will check the relevant literature tomorrow. The physics of blown sand is well understood, since the benchmark studies of Bagnold in the 30's.
Cheers
Jon
