Looks like a stem of some kind. I’m arguing stem and not leaf because 1) I don’t see venation and 2) It appears that there are lateral shoots coming off of it. Could be some sort of Progymnosperm or Pteridospermatophyte (depending on your classification scheme) or a Cordaixylon. It’s a seed plant if that helps. I’m not as familiar with the area but given the age and texture of the stem it’s safe to rule out other Carboniferous plants like Calamites, Lepidodendron, Sagellaria and all of the tree ferns.
Thank you for helping with this fossil. Yes, I noticed the lateral shoots. Because of their presence, it had to be a stem or root. I was a bit surprized to see the impression with marine fossils. At least the field of possible plants is narrowed. If there were leaves ID would be easier. Maybe next summer, I will find another with more elements to aid in identification.