Those microscopic fossils may well be just "along for the ride." Finding an ancient man's body in a snowbank does not prove that glaciers derive from decayed humans.
Quite right. Now, where does the Earth get these particular fossils, 100 miles underground where petroleum is ostensibly produced? Wouldn't most of the (non-biological) petroleum end up in completely different layers, or (more likely) associated with igneous rocks? How is it possible that paleontologists can help to locate oil deposits by looking at the types of fossils, if the fossils are very old, but the petroleum deposits are not?