Any given point in the rock record indicates a given location throughout the depositional history. As the depositional environment changes so will the type of rock laid down. As the sea level moves across a given point different forms of rock are deposited in a predictable manner.
In the near shore environment the materials deposited will be coarser, frequently sands. As the water deepens during a marine transgression, the sediment is still clastic, but much finer grained, resulting in a shale lithology. In the deep water, the deposition is primarily organic, resulting in limestone deposits. Finally, as sea level drops and the shoreline begins regress, the sequence appears again in reverse.