>"The commonest sites for the development of mudcracks are water-
>saturated sediment surfaces which are exposed subaerially, such
>as surfaces of dried up ponds, coastal and inland sabkha, lakes
>and lagoons; abandoned river channels; flood plains, and
>intertidal zones. In these areas mudcracks are usually
>associated with other features of subaerial exposure, such as
>raindrop imprint, hailstone imprints, etc. A combination of such
>features constitutes one of the best indicators of intermittent
>subaerial exposure of a sedimentation surface."~ p. 59-60 H. E.
>Reineck J. B. Singh Depositional Sedimentary Environments New
>York: Springer-Verlag 1980
Such cracks can and are known to have been produced subaqueously by
histeresis shrinkage of chemically shortened clays. This is not to say
that all mud cracks formed that way, just to sound a cautionary note to any
dogmatic assertion.
Art
http://chadwicka.swau.edu