Just been digging around in the rock pile, and I found this rock which I'd recently described in a USENET post:
The cohesiveness of consolidated mud would provide a comparatively resistant surface over which coarser-grained sediments could be transported as a package. Actually, thinking about it, I've a nice specimen in my rock pile showing a similar event from 100-odd million years ago. Mid-jurassic of the Isle of Wight, there was a muddy sea-bottom with a rich fauna of burrowing worms chomping away buried in their nice muddy burrows. Then along came a flood of silty sand which buried and killed off the worms leaving a series of sandy casts of the top ends of the burrows on the *under* surface of a circa-2cm thick sand bed. One hundred million years later along comes a superannuated hippie of a geology student who extracts said thin sand bed from a 10-odd metre high cliff of similarly interbedded muds and sands, and carefully appreciates the day in the death of these worms before spending hours in the pub (and back in the honours year student labs) carefully picking out the bits of clay from between the casts of the burrows.
"AA" size cell and a ruler to give scale objects. The autofocus of the camera seems to be slipping, and there's no manual alternative. I'm thinking that I can almost justify getting a new camera.
Carsten described these as "escape structures". I don't think so - I think they're burrows which the worms (lugworm or equivalent) died in after getting a belly full of sand. The underlying mudstone bed contains sub-vertically oriented sand tubes dispersed through the mud, representing the worms which swallowed a sand meal, stopped eating, swallowed (separating the swallowed sand from the continuous sheet), then died.
Please note that this photograph is of the UNDERSIDE of the slab as originally found, in a normally oriented sediment sequence.