outline stratigraphy: –study of the layers of sedimentary rocks unconformities correlation...
TRANSCRIPT
Outline• Stratigraphy:
– Study of the layers of sedimentary rocks
• Unconformities• Correlation• Relative dating• Absolute dating
Optional Field Trip ExerciseChanged from March 18 to
March 4Due March 9 at 1:10 pm
Zuhl Museum
Alumni Center, 775 College Av.
Sedimentation inlake or sea
Sedimentation inlake 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
TIME 1 Beneath the sea, sediments accumulated in beds.
B
C
D
A
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)
Cardenas Basalt (1.1 billion years)
Angular Unconformity
Nonconformity: seds over granite
Nonconformity
Sequence of events:
1) Deposition of sediment2) Tilting of beds3) Erosion4) Deposition of sediment
Write down the sequence of events for this location.
1. Deposition of sediment
1. Deposition of sediment2. Folding 3. Erosion4. Deposition of sediment
on top
TIME 1 Beneath the sea, sediments accumulated in beds.
B
C
D
A
TIME 2 Tectonic forces caused uplift, exposing the beds to erosion.
B
C
D
A
Uplift
TIME 3 Erosion stripped away bed D and part of C.
B
C
A
TIME 4 Subsidence allowed a new layer, E, to be deposited.
BC
A
E
Subsidence
Unconformity
TIME 1 Beneath the sea, sediments accumulated in beds.
TIME 2 Tectonic forces caused uplift, folding, and deformation.
Uplift
Compression
TIME 3 Erosion stripped away the tops of the folded layers, leaving portions of several layers exposed.
TIME 4 Subsidence allowed new sediments to be deposited.
Subsidence
Angularunconformity
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 Outcrop B
III
II
III
Outcrop A Outcrop B
III
II
III
Outcrop A Outcrop B
III
II
III
Outcrop A Outcrop B
III
II
III
Some of the fossils found inoutcrop A are the same as fossils found in outcrop B, some distance away.
Outcrop A Outcrop B
III
II
III
Some of the fossils found inoutcrop A are the same as fossils found in outcrop B, some distance away.
Layers with the same fossils are the same age.
Outcrop A Outcrop B
III
II
III
Some of the fossils found inoutcrop A are the same as fossils found in outcrop B, some distance away.
Layers with the same fossils are the same age.
Stratigraphicsuccession
A composite of the two outcrops.
Younger rocks
Older rocks
I
II
III
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 killed70% land vertebrates killed
End of the Paleozoic
Mesozoic-Ammonites
Mesozoic-Ammonites
Mesozoic-Triceratops
Cretaceous-Tyrannosaurus
Rex
End of the Mesozoic
Major extinction event:85% of all species died.
Cenozoic-Mammoth
Cenozoic-Sabre tooth tiger
Summary
Principle of superpositionPrinciple of original horizontality
Principle of faunal successionUnconformities
Time scaleEvolution of life