Relative dating of sedimentary rocks asking question for dating
However, it is possible that the granite may have intruded as a magma within the crust, beneath conglomerate, after the conglomerate formed.
If so, the granite is younger and the boundary between the granite and the conglomerate is an intrusive contact rather than a nonconformity.
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.
A major unconformity would mark the change from the building up of mountains to the wearing down of those same mountains and the subsequent blanketing of the area with sediments.
Nonconformities mark major chapter breaks in the geologic history of an area.
In the example below, the contact between the conglomerate and the granite beneath it appears likely to be a nonconformity.
They did not know how many thousands, millions, or billions of years ago the Cambrian period began, but they knew that it came after the Proterozoic Eon and before the Ordovician Period, and that the fossils unique to Cambrian rocks were younger than Proterozoic fossils and older than Ordovician ones.
A nonconformity is an unconformity with sedimentary or volcanic strata on top and, beneath it, either plutonic rock such as granite or metamorphic rock such as schist.
Because granitic and metamorphic rocks form deep in the earth's crust, a significant amount of time is required for uplift and erosion to expose them.
What would the geologist be able to deduce about the world we live in, based on what was left in the strata?
Stratigraphy started to become a formal science due to the work of a man who published under the name Nicolaus Steno in the 17th century.