Stratigraphers have codified a basic concept of their discipline in the Law of Superposition , which simply states that , in an undeformed stratigraphic sequence , the oldest strata occur at the base of the sequence .
One of stratigraphy 's basic concepts is codified in the law of superposition , which simply states that , in an undeformed stratigraphic sequence , the oldest strata occur at the base of the sequence .