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In the example below, the contact between the conglomerate and the granite beneath it appears likely to be a nonconformity.
However, it is possible that the granite may have intruded as a magma within the crust, beneath conglomerate, after the conglomerate formed.
An unconformity marks a "gap in geologic time" because the rocks below and above it come from widely separated geologic times.
Unconformities separate chapters in the geologic history of a given region.
For instance, an orogenic episode (a long geologic episode of mountain building) may finally come to end and the eroded mountains may be buried beneath a new sequence of sediments.
After being tilted or folded, the older layers of sediment were eroded.
Then younger layers of sediment were deposited on them.