Some Features on the Nugget/Navajo Sandstone, San Rafael Swell, Utah
A dinosaur track in the top of the Jurassic Nugget Sandstone (also called the Navajo Sandstone) on the San Rafael Swell, Utah. This was located in the bottom of a wash and has since been covered or eroded away. The middle toe must have been loaded with mud as the dinosaur stepped into this spot.
An interesting structure on the same surface as the dino print above. I thought this might be a burrow of some type, but my friend and colleague, Dr. Steven Hasiotis, who is an expert in trace fossils was unconvinced. We decided it must be some kind of fluid "pebble dike" like structure, where the solid sandstone was broken up and then redeposited as water or other fluids moved through the rock.
Also found on the Nugget Sandstone on the San Rafael Swell, this picture shows the individual avalanche deposits of sand that tumbled down the dune face before this became a rock.
Here is another view of this dune in the Nugget Sandstone. You can see the surface with the avalanche deposits in the foreground and in the background a lower face of the dune that is covered with ripples.
In one spot on this petrified dune, there were these small circle-like structures (see piece of chalk for scale). I am not sure what caused them.
Just below the dunes shown above, the sandstone is ribbed with giant polygonal cracks filled with sandstone that is slightly more resistant to erosion. My colleague, Ron Blakey at Univ. of Northern Arizona has published several papers on these structures.
One of the most interesting features to me found on a couple of the dune faces were these triangular and rectangular structures. They represent salt or gypsum that crystallized in the sand and, after leaving an impression, dissolved away.
Another probable dinosaur undertrack on the top of the Nugget.
Along the edge of the wash, a series of these possible dino tracks seem to form a trackway.