Diachronous

A diachronous (Greek dia, through + Chronos) deposit in geology is a sedimentary rock formation in which apparently similar material varies in age from place to place.

Typically this occurs as a result of a marine transgression or regression, or the progressive development of a delta. As the shoreline advances or retreats, a succession of continuous deposits representing different environments (for example beach, shallow water, deeper water) may be left behind. Although each type of deposit (facies) may be continuous over a wide area, its age varies according to the position of the shoreline through time.