Relative Dating and Sequencing Notes!
Relative Dating and Sequencing
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Relative vs. Absolute Time
Laws
Unconformities
Correlating Geologic Cross Sections
________________:
• Ages of events are placed in order of
occurrence.
• No exact date is identified.
– Ex. WWI and WWII
– I am the second child in my family.
– Mr. Williams is mad old, yo
_________________:
• identifies the exact date of an event.
– Ex. 65 Million Years Ago
– 1990
Nicholas Steno
• First Things First…or…
“How’d that get there?”
• In the 17th C., Nicolas Steno made an important observation:
"Sediments are usually deposited in __________ layers."
He called this
“ORIGINAL _______________”
1. The Law of ______________ - in a sequence of
undisturbed sedimentary rocks, the oldest rocks
will be at the bottom.
2. The law of _________________ relationships – anything
that cuts across layers of rock is younger than the
rocks that it has intruded into. This applies to
faults and igneous intrusions.
3. The law of ______________ fragments - the
fragments that make up a rock are older than
the entire sample.
4. The Law of _________or _______: tilts in rocks are
younger than the rocks themselves.
5 The Law of Original ____________- Rocks are
usually deposited flat and level.
6. Cole’s LawThinly sliced cabbage.
Contact Metamorphism!
• ___________________ shows that the rock that was
changed was there first when the intrusion
happened.
Formation of an unconformity
• An ___________________ is an old buried surface that was eroded
• Over time, new rock layers were deposited on it
• Sometimes layers of rock are missing
• There is a break or gap of ______________ not represented by the layers in
an area. The gap represents an unknown length of time
• No way of knowing exactly what happened but we do know ____________
exposed rocks to weathering and erosion.
• Rocks above unconformity are ______________ – rocks below _______
How is an unconformity formed?
1. ___________– area of crust uplifted above sea level
(deposition – under water)
2. ___________ – some time after
3. ___________ (subsidence) below sea level
4. ___________ – new sediments deposited on top of the
buried eroded surface