The correct answer is carbon film.
A carbon film or the carbonaceous film refers to a species outline of a fossil. It is a kind of fossil found in any rock when an organic substance is compressed, leaving behind the carbon film or residue.
When a species is buried beneath the various layers of sediment, the heat and pressure pile up. These circumstances make the liquids and gases to expel from the body, leaving behind a thin film of carbon residue, producing an outline of the original species known as a carbon film.