The increasingly inaccurately named image of the "week" series continues. Since I've failed to post any of these for a few weeks, I'm going to post several images. In honour of the Boudin Centennial (which you can read more about here, but only if you subscribe to the Journal of Structural Geology), these are boudin-like structures that occur in slumps in the Albert Formation of New Brunswick, Canada:
Here's a layer beginning to break up into the boudin-like structures.
You can see a couple of the boudin-like structures here, to the right of the notebook.
This is within a slump unit, and you can see that there are fragments of fold hinges and aerofoil-shaped fold fragments that have become detached from the rest of their parent layers. I think what happens is that these isolated fragments then get rolled up as slumping continues, and you end up with something like this:
A polished section of one of the boudin-like structures, showing internal folding.
This one has a sheath-fold, if you look in the top left of the image. Not sure about this, but perhaps along-boudin extension occurs as the "boudin" gets flattened and rolls during slumpiing, analogous to rolling out a piece of plasticine.
Playground example of gravity-driven deformation
2 years ago