Of course there is no proof that confirm fossilization took place in each sedimentary rock. These methods are applicable to materials that are up to aboutyears old. The principles of original horizontality, superposition, and cross-cutting relationships allow events to be ordered at a single location. You can learn more about fossils, dinosaurs, radiometric dating and related topics by reading through the links below.
Some of the isotopes used for this purpose are uranium, uranium and potassiumeach of which has a half-life of more than a million years.