This looks for all the world like a diagenetic oxidation halo around a bar-shaped fossil (crinoid pluricolumnal?), caused by bacterial activity after the death of the animal. Especially given the halos around the other fossils in the same rock.
If this were the Hunsrück Slate, I would give more pause. But since soft-bodied preservation is unheard of anywhere else in the Devonian, and since Appalachia’s Devonian rocks are sufficiently well studied that we would know about instances of soft-bodied preservation, there is no good reason to consider the possibility here. Just a diagenetic halo.