A set of
parallel or
reticulate ridges, usually less than 1
millimetre high and spaced at a few millimetres on
cohesive muddy
sediment surfaces.
These marks form in intertidal environments when strong wind stress affects the surface of the sediment when covered by a very thin film of water, or by the action of subaqueous currents or sediment loading.
In other words, runzelmarken is the geological term for those peculiar wavy patterns you sometimes see on beach sand or in shallow mudflats.
Runzelmarken is also known as wrinkle marks, which unfortunatly doesn't sound anywhere near as exciting or scientific.