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.