Answer:
Disconformity
Step-by-step explanation:
Disconformities are usually erosional contacts that are parallel to the bedding planes of the upper and lower rock units.
Since disconformities are hard to recognize in a layered sedimentary rock sequence, they are often discovered when the fossils in the upper and lower rock units are studied.
A gap in the fossil record indicates a gap in the depositional record, and the length of time the disconformity represents can be calculated.
Disconformities are usually a result of erosion but can occasionally represent periods of non-deposition.