by Michael Steinbacher
While hosting a geology tour one year ago, we passed the formation from the link below.
It has layers of dark material that might be coal or shale. The only way to get such vertical layers from a dune would be to have the formation fold after deposition. That seemed possible but something of a stretch. This caused a re-examination of the dune process.
Sand dunes grow with the direction of the wind. Dry sand bounces along the desert and up the windward side of a dune. When the bouncing sand gets to the ridge, the sand falls down the slip face, increasing the size of the dune in the direction of the wind.
If the blowing material was wet, conglomerate (dirt with various sizes of rocks), or molten, it would stick to the windward side and grow up and back into the wind. This now appears to be the process I misconstrued as duning. I was only wrong by 180 degrees.