Dear WW: I have no idea. The important thing that Anita Harris noted was that during the process of changing marine deposits containing methane into petroleum, the conodonts
had a characteristic color change. So where you found changed conodonts, you might find petroleum. But again,
there had to be a layer above that would keep both methane and petroleum from escaping. That I learned from McPhee's book. You might think geology a dry subject, but McPhee
makes it fascinating reading. (Annals of the Former World)