Final answer:
The occurrence of sandstone directly underlying shale is an example of a lithostratigraphic relationship that represents lateral changes in sediment deposition, which can be an onlap sequence.
Step-by-step explanation:
When sandstone directly underlies shale in a vertical sequence, it is an example of a lithostratigraphic relationship that reflects changes in the depositional environment of these sedimentary rocks. According to Walther's Law, this vertical arrangement represents the lateral changes in the environment that occurred as sediments were deposited. In the context of the sea-level changes you've described, as mentioned in sequence stratigraphy, when sea level rises, deposition of sediments shifts toward the coastline, which can result in an onlap sequence, where sediments are deposited against the sloping surface of the older clinoforms. Conversely, when sea level lowers, this is known as a regression, and can result in offlap sequences. Sequences like these are key in interpreting the geological history of an area.