Naah, I'm afraid the petrol comes from animalcules and vegetation.

After 150 million years there won't be anything left of our civilization that could be recognized as being "artificial" either.

Not sure about that. Isaac Asimov, I think it was, wrote a story in which people in the future were puzzling over these strange ceramic artifacts that were all over the place, and theorising what they might be for. They were lavatory pans. I think they'd survive pretty well.

Now what would a civilised dinosaur's lavatory pan be like? I mean, they haven't been looking for things like that have they...