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Outline
• Stratigraphy:
– Study of the layers of sedimentary rocks
•
•
•
•
Unconformities
Correlation
Relative dating
Absolute dating
Optional Field Trip Exercise
Changed from March 18 to
March 4
Due March 9 at 1:10 pm
Zuhl Museum
Alumni Center, 775 College Av.
Sedimentation in
lake or sea
Sedimentation in
lake or sea
Sediments are deposited in horizontal
layers and slowly change into rock.
Principle of Original
Horizontality
• In stratigraphy:
• Sedimentary layers are originally deposited
as horizontal sheets.
• Folded or tilted beds indicates something
happened to them later
D
C
B
A
TIME 1
Beneath the sea, sediments
accumulated in beds.
Principle of Superposition
• In stratigraphy:
• Sedimentary layers at the bottom of a
sequence are OLDER than the ones on top
• If older beds are on top, then the sequence
has been turned upside down
Younger
Older
Unconformities: Missing time
Tapeats Sandstone (500 million years)
Angular Unconformity
Nonconformity: seds over granite
Nonconformity
Sequence of events:
1)
2)
3)
4)
Deposition of sediment
Tilting of beds
Erosion
Deposition of sediment
Write down the sequence
of events for this
location.
1. Deposition of
sediment
1.
2.
3.
4.
Deposition of sediment
Folding
Erosion
Deposition of sediment
on top
D
C
B
A
TIME 1
Beneath the sea, sediments
accumulated in beds.
D
C
B
A
TIME 2
Tectonic forces caused
uplift, exposing the beds
to erosion.
Uplift
C
B
A
TIME 3
Erosion stripped away
bed D and part of C.
E
C
B
A
TIME 4
Subsidence allowed a new
layer, E, to be deposited.
Subsidence
Unconformity
TIME 1
Beneath the sea,
sediments accumulated in beds.
Compression
TIME 2
Tectonic forces caused
uplift, folding, and deformation.
Uplift
TIME 3
Erosion stripped away the
tops of the folded layers, leaving
portions of several layers exposed.
Angular
unconformity
TIME 4
Subsidence allowed new
sediments to be deposited.
Subsidence
Plants grow on this surface
10 cm
Principle of Faunal Succession
• In stratigraphy:
• Fossils appear in a definite sequence
• This sequence can be used to CORRELATE
beds in one area to another
Outcrop A
I
Outcrop B
II
II
III
Outcrop A
I
Outcrop B
II
II
III
Outcrop A
I
Outcrop B
II
II
III
Some of the fossils found in
outcrop A are the same as
fossils found in outcrop B,
some distance away.
Outcrop A
I
Outcrop B
II
II
III
Some of the fossils found in
outcrop A are the same as
fossils found in outcrop B,
some distance away.
Outcrop A
Outcrop B
I
II
II
Layers with the
same fossils are
the same age.
III
Some of the fossils found in
outcrop A are the same as
fossils found in outcrop B,
some distance away.
Outcrop A
Outcrop B
I
II
II
Layers with the
same fossils are
the same age.
III
Stratigraphic
succession
Younger rocks
I
II
III
Older rocks
A composite of the two outcrops.
The Age of the Earth
4,560,000,000 years
or 4.6 billion years
Geologic Time Scale
• Precambrian (4.6 Ga to 540 Ma)
• Paleozoic (540 Ma to 250 Ma)
• Mesozoic (250-65 Ma)
– Triassic
– Jurassic
– Cretaceous
• Cenozoic (65 Ma to the present)
LIFE ON EARTH
3.5 billion year old bacteria
and algae
Cambrian explosion of life:
540 million years ago
Trilobites-Paleozoic arthropods
Today: 80% of species are arthropods
another Trilobite
Crinoids
First land
animals:
365 Ma
Dimetrodon-Permian reptile
End of the Paleozoic
Major extinction event:
96% of marine life was killed
70% land vertebrates killed
End of the Paleozoic
Mesozoic-Ammonites
Mesozoic-Ammonites
Mesozoic-Triceratops
CretaceousTyrannosaurus
Rex
End of the Mesozoic
Major extinction event:
85% of all species died.
Cenozoic-Mammoth
Cenozoic-Sabre tooth tiger
Summary
Principle of superposition
Principle of original horizontality
Principle of faunal succession
Unconformities
Time scale
Evolution of life