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STRATIGRAPHY&GEOLOGICTIME

Stratigraphy:Studyofthelayersofsedimentaryrocks

Unconformities Correlation GeologicTime

Scale

Sedimentation inlake or sea

Sediments are deposited in horizontallayers and slowly change into rock.

StratigraphicPrincipalofOriginal

Horizontality

Sedimentarylayersareoriginallydepositedas.

Foldedortiltedbedsindicatessomethinghappenedtothemlater

TIME 1Beneath the sea, D

sedimentsaccumulated in beds. B

C

A

StratigraphicPrincipalof

Superposition

SedimentarylayersatthebottomofasequenceofbedsareOLDERthantheonesontop

Ifolderbedsareontop,thenthesequencehasbeenturnedupsidedown

Younger

Older

PrincipleofSuperposition

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Stratigraphic Principal ofCross-Cutting Relations

Any rock or structure that cutsacross another rock is younger thatthe rock it cuts across.

Unconformity=

surface

of

nondepositionorerosion

Tapeats Sandstone (ca.500 million years)

Angular Unconformity

Beds below the unconformitysurface are at an angle to the bedsoverlying the surface

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Angularunconformity Unconformitywherebedsbelowareatanangletobeds

above

Nonconformity

Unconformity wherebeds overliemetamorphic origneous rocks

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Angularunconformity Unconformitywherebedsbelowareatanangletobeds

above

TIME 1Beneath the sea,

sediments Daccumulated in beds.

B

C

A

TIME 2Tectonic forcescaused uplift,

C

D

to erosion.

B

A

Uplift

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TIME 3 C

Erosion strippedaway bed D andpart of C.

B

A

DisconformitySurface between horizontal strata wheremajor erosion or non-deposition occurred

Subsidenceallowed a newlayer, E, to bedeposited.

B

C

A

E

Subsidence

Unconformity

10 cm

TIME 1Beneath the seasedimentsaccumulated in beds.

Compression

TIME 2Tectonic forces causeduplift, folding, anddeformation.

Uplift

TIME 3Erosion stripped away

layers, leavingportions of severallayers exposed.

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TIME 4Subsidenceallowed new

sediments to bedeposited.

An ular

Subsidence

unconformity

Write down thesequence of events forthis location. There areat least 5.

1. Deposition of redsiltstone sediment

2. Lithification ofsediments

3.4.5.

1. Deposition ofsediment

2. Compaction/cement= sedimentary rock

3. Folding (syncline)4. Erosion -angular

unconformity

5. Deposition ofsediment on top

Plants grow on this

surface

StratigraphicPrincipalof

FaunalSuccession

Fossilspeciesappearanddisappearina

.

ThissequencecanbeusedtoCORRELATEbedsinoneareatoanotherarea.

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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

Some of the fossils found inoutcrop A are the same asfossils found in outcrop B,some distance away.

II

III

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Outcrop A Outcrop B

III

Some of the fossils found inoutcrop A are the same asfossils found in outcrop B,some distance away.

II

III

Layers with thesame fossils arethe same age.

Outcrop A Outcrop B

III

Some of the fossils found inoutcrop A are the same asfossils found in outcrop B,some distance away.

II

III

Layers with thesame fossils arethe same age.

Younger rocks

I

II

A composite of the tw o outcrops.

Older rocks

III

TheAgeoftheEarth

4,560,000,000 years

or 4.6 billion years

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GeologicTimeScale

Precambrian(4.6Gato540Ma)

Paleozoic(540Mato250Ma)

Triassic

Jurassic

Cretaceous

Cenozoic(65Matothepresent)

LIFEONEARTH

3.5billion

year

old

bacteria

andal ae

PaleozoicEra

Cambrianexplosionoflife:

540millionyearsago

TrilobitesPaleozoicarthropods

Today: 80% of species are arthropods

anotherTrilobite Crinoids

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First land

animals:365 Ma

Dimetrodon Permianreptile

EndofthePaleozoic

Major extinction event:96% of marine life was killed70% land vertebrates killed

EndofthePaleozoic

MesozoicEraAmmonites MesozoicEraAmmonites

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MesozoicEraTriceratops

MesozoicEra

CretaceousPeriod

Tyrannosaurus

Rex

EndoftheMesozoic

Ma or extinction event:85% of all species died.

CenozoicMammoth

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CenozoicSabretoothtiger

EndoftheCenozoic?

Supervolcano eruption

SupernovaMeteorite im act

Nuclear warEpidemic

Global warming...