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.The key to identifying each specific type of unconformity is recognizing what the unconformity is on top of.
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.
An angular unconformity is an unconformity beneath which the strata were tilted or folded before deposition of the younger layers of sediment above the unconformity.
After being tilted or folded, the older layers of sediment were eroded.
Instead, there is just an unconformity, a buried erosional or non-depositional surface.
Unconformities separate chapters in the geologic history of a given region.To determine the nature of the contact - whether it is an intrusive contact or a nonconformity - further evidence from field investigations would be needed.Evidence such as angular pieces of conglomerate surrounded by the granitic intrusion, and contact metamorphism of the conglomerate adjacent to the granite, would indicate that the granite is younger and intruded the older conglomerate.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.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.