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

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 sediment 2)Tilting of beds 3)Erosion 4)Deposition of sediment

Write down the sequence of events for this location. 1.Deposition of sediment

2.Folding 3.Erosion 4.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. B C 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 Angular unconformity

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 AOutcrop B I II III

Outcrop AOutcrop B I II III

Outcrop AOutcrop B I II III

Outcrop AOutcrop B I II III Some of the fossils found in outcrop A are the same as fossils found in outcrop B, some distance away.

Outcrop AOutcrop B I II III Some of the fossils found in outcrop A are the same as fossils found in outcrop B, some distance away. Layers with the same fossils are the same age.

Outcrop AOutcrop B I II III Some of the fossils found in outcrop A are the same as fossils found in outcrop B, some distance away. Layers with the same fossils are the same age.

Stratigraphic succession 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 ( 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-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 superposition Principle of original horizontality Principle of faunal succession Unconformities Time scale Evolution of life