Metamorphic. I looked up some rocks and I’m including the picture of it and it shows something similar to your picture and it says it’s a metamorphic rock.
For the answer to the question above, I think that Few Fossils exist from this time because the animals were all soft-bodied. Most of the animals dissolve or decompose immediately and turn to dust because they are soft-bodied.
Either the duodenum or the jejunum
3D paint on a computer or 3D printer hope it helps:)