That is an interesting question. With coal we have peat, lignite, subbitumunious, bituminous and anthracite as some of the main steps. However, I have not heard of anything similar for oil representing “unfinished oil.” Anyone??
With coal we have peat, lignite, subbitumunious, bituminous and anthracite as some of the main steps.That's the gradualist view, but the evidence is for sudden deposition of deposits, rapid burials. This isn't to say that this didn't take place many times over millions of years of course.