As I was collecting at Arkona in the Widder Fm yesterday, my eye was drawn to this piece. It had a lot going for it - apparent texture, concentric ribbing, suggestive shape. Not knowing for sure at that moment, and not wanting to spend valuable collecting time deliberating on it when I had a lot of shale to move, I simply put it in the bucket so that I could take a closer look when I got home.
My question for those who know more about taphonomy and such would be this: can anyone tell me a bit more on the processes that produce this kind of nodular form? The concentric patterns are