The stuff you saw on the dirt road is most likely not petroleum based oil. The road I live on is unpaved, ie gravel with lots of dry dusty dirt underneath. The town used to put a solid, granular stuff to keep the dust down, but have switched to a liquid. It looks a lot like oil, but doesn't work as well. It does get picked up by car and bike tires, which then look like they have oil on them.
I heard rumors that the town might chip seal the road, it's only 1/4 long, but I live at the very end. So I guess I'd have to walk the road bike to the other end when I want to ride it. I don't which would be worse, the CS or the dust/mud.