Relative Age Flashcards
Relative age:
The order/sequence known, but not the actual date of occurence
Uniformitarianism:
-Introduced by James Hutton in the 1700s
-The idea that the processes that shaped the
Earth today are the same processes that
occurred in the geologic past
Original horizontality:
-Introduced by Nicolas Steno in the 17th century
-Sediments are usually deposited in
horizontal layers
Superposition:
A sedimentary sequence
will be oldest on bottom (if undisturbed).
Cross-cutting:
The rock is always
older than the processes that changed it
Example: a body of igneous rock is younger than rock it has intruded (cut across)
Included fragments:
Pieces of rock found in another rock must be older (formed first)
Igneous intrusion:
Occurs when magma squeezes into or between layers of pre-existing rock
Unconformity:
A buried surface of erosion separating two rock masses
What does an unconformity represent?
A gap in geologic time
Angular unconformity:
An unconformity in which the beds below the unconformity dip at a different angle than the beds above
Disconformity:
An unconformity in which the beds above the unconformity are parallel to the beds below the unconformity, though the layers are “missing”
Nonconformity:
An unconformity that seperates profoundly different rock types, such as sedimentary rocks from metamorphic rocks
Stress:
A force that is capable of greatly deforming rocks, and may result in the folding or faulting of rock
Faults:
Cracks or fractures in rocks caused by stress
Folds:
“Bends” in rock layers
