Relative Dating – LabRelative Dating – Lab

Which geologic event occurred first??Which geologic event occurred first??

Which rock layer formed first?Which rock layer formed first?

How do you know?How do you know?

Which rock layer formed first?Which rock layer formed first?

How do you know?How do you know?

Geologic relative dating LabGeologic relative dating LabGeologic relative dating LabGeologic relative dating Lab

Relative Dating:

Unraveling earth history by placing geologic events in

chronological order

“Which geologic process came first”?

Relative Dating:

Unraveling earth history by placing geologic events in

chronological order

“Which geologic process came first”?

NO actual numbers applied!NO actual numbers applied!

Objectives:Objectives: •To observe exposures of rock and decipher To observe exposures of rock and decipher

the geologic historythe geologic history

•Use relative dating principles to unravel Use relative dating principles to unravel geologic historygeologic history

Objectives:Objectives: •To observe exposures of rock and decipher To observe exposures of rock and decipher

the geologic historythe geologic history

•Use relative dating principles to unravel Use relative dating principles to unravel geologic historygeologic history

Which layer was deposited firstA,B,C,D, or E??Which layer was deposited firstA,B,C,D, or E??

A

B

C

D

E

Igneous dikeIgneous dike

Let’s unravel some geologic history from observations of Let’s unravel some geologic history from observations of various formations and their contactsvarious formations and their contactsLet’s unravel some geologic history from observations of Let’s unravel some geologic history from observations of various formations and their contactsvarious formations and their contacts

Nicholas Steno – 1669 proposed the following relativeNicholas Steno – 1669 proposed the following relativedating principlesdating principlesNicholas Steno – 1669 proposed the following relativeNicholas Steno – 1669 proposed the following relativedating principlesdating principles

The principle of Original Horizontality:•Sedimentary rock layers are deposited as horizontal strata•Any observed non-horizontal strata has been disturbed

The principle of Original Horizontality:•Sedimentary rock layers are deposited as horizontal strata•Any observed non-horizontal strata has been disturbed

Sediment input

AABB

CC

Strata has been deposited in horizontal layersOriginal Horizontality

Strata has been deposited in horizontal layersOriginal Horizontality

The principle of The principle of SuperpositionSuperposition

• In any undisturbed sequence of strata, the In any undisturbed sequence of strata, the oldest stratum is at the bottomoldest stratum is at the bottom of the of the sequence and the youngest stratum is on top.sequence and the youngest stratum is on top.

The principle of The principle of SuperpositionSuperposition

• In any undisturbed sequence of strata, the In any undisturbed sequence of strata, the oldest stratum is at the bottomoldest stratum is at the bottom of the of the sequence and the youngest stratum is on top.sequence and the youngest stratum is on top.

11

22

33

44

55

Oldest

Youngest

Which strata are older and younger??Which strata are older and younger??

OldestOldest

YoungestYoungest

The principle of The principle of InclusionsInclusions

•A piece of rock (clast) that has become “included” A piece of rock (clast) that has become “included” in another rock body is in another rock body is olderolder than the rock body than the rock body it has become part of – why?it has become part of – why?

The principle of The principle of InclusionsInclusions

•A piece of rock (clast) that has become “included” A piece of rock (clast) that has become “included” in another rock body is in another rock body is olderolder than the rock body than the rock body it has become part of – why?it has become part of – why?

Rock body Rock body AARock body Rock body AA

Intrusion of pluton BIntrusion of pluton BIntrusion of pluton BIntrusion of pluton B

AAAA AA

Older (rock A was there first)Older (rock A was there first)

Which “granites” are older and younger?Which “granites” are older and younger?

OLDEROLDERYOUNGERYOUNGER

The principle of The principle of Cross Cutting relationshipsCross Cutting relationships

•Any geologic feature that cuts across another geologicAny geologic feature that cuts across another geologic feature is feature is youngeryounger

The principle of The principle of Cross Cutting relationshipsCross Cutting relationships

•Any geologic feature that cuts across another geologicAny geologic feature that cuts across another geologic feature is feature is youngeryounger

1

2

3

4

5

6

Is layer 5 olderor younger thanthe intrusivedike ??

Is layer 5 olderor younger thanthe intrusivedike ??

Which dikes formed first?

ABC

Qtz-Asp Vn

1

2

3

6

7

Given this sequence of rock layers, “What’s wrong with the timing of events????Given this sequence of rock layers, “What’s wrong with the timing of events????

OldestOldest

YoungestYoungestA time of erosionor non-deposition

“missing time”

A time of erosionor non-deposition

“missing time”

The principle of The principle of UnconformitiesUnconformities

•Rock surface that represents a period of erosion or non Rock surface that represents a period of erosion or non depositiondeposition•Referred to “missing time”Referred to “missing time”•Three major types of unconformitiesThree major types of unconformities

•DisconformityDisconformity•Angular unconformityAngular unconformity•Non-conformityNon-conformity

The principle of The principle of UnconformitiesUnconformities

•Rock surface that represents a period of erosion or non Rock surface that represents a period of erosion or non depositiondeposition•Referred to “missing time”Referred to “missing time”•Three major types of unconformitiesThree major types of unconformities

•DisconformityDisconformity•Angular unconformityAngular unconformity•Non-conformityNon-conformity

UnconformityUnconformity

DisconformityDisconformity – uncon in non-disturbed sedimentary uncon in non-disturbed sedimentary layerslayersDisconformityDisconformity – uncon in non-disturbed sedimentary uncon in non-disturbed sedimentary layerslayers

Angular unconAngular uncon – – uncon lies between angled stratauncon lies between angled strata and overlying horizontal strataand overlying horizontal strataAngular unconAngular uncon – – uncon lies between angled stratauncon lies between angled strata and overlying horizontal strataand overlying horizontal strata

Non-conformity Non-conformity – – sedimentary stratasedimentary strata overlies crystallineoverlies crystalline rocks (ig and met)rocks (ig and met)

Non-conformity Non-conformity – – sedimentary stratasedimentary strata overlies crystallineoverlies crystalline rocks (ig and met)rocks (ig and met)

Xln rocksXln rocks

Sedimentary rocksSedimentary rocks

DisconformityDisconformity

AngularUnconformity

AngularUnconformity

NonconformityNonconformity

Let’s apply the principles and unravel earth’s historyLet’s apply the principles and unravel earth’s historyWhich came first? -- start with oldest to youngestWhich came first? -- start with oldest to youngestLet’s apply the principles and unravel earth’s historyLet’s apply the principles and unravel earth’s historyWhich came first? -- start with oldest to youngestWhich came first? -- start with oldest to youngest

A

B

C DE

F

G

H

I

Deposition of layers Deposition of layers E,D,C,B,AE,D,C,B,ADeposition of layers Deposition of layers E,D,C,B,AE,D,C,B,A

Tilting of layersTilting of layersE,D,C,B,AE,D,C,B,ATilting of layersTilting of layersE,D,C,B,AE,D,C,B,A

Angular Uncon FAngular Uncon FAngular Uncon FAngular Uncon F

Deposition of layers Deposition of layers G,H,IG,H,IDeposition of layers Deposition of layers G,H,IG,H,I

oldestoldestoldestoldest

youngestyoungestyoungestyoungest

Rock symbols (rock legends) Rock symbols (rock legends) Rock symbols (rock legends) Rock symbols (rock legends)

Understand the various types Understand the various types of rock (lithologic) symbols in of rock (lithologic) symbols in conjunction to the principles to conjunction to the principles to determine the geologic historydetermine the geologic historyof an area.of an area.

Understand the various types Understand the various types of rock (lithologic) symbols in of rock (lithologic) symbols in conjunction to the principles to conjunction to the principles to determine the geologic historydetermine the geologic historyof an area.of an area.

deposition

emplacement

The principle of Faunal (fossil) successionThe principle of Faunal (fossil) succession

This principle is attributed to William Smith, an English engineer in the late 1700s. Smith noticed that the kinds of fossils he found changed through a vertical succession of rock layers, and furthermore, that the same vertical changes in fossils occurred in different places.

This principle is attributed to William Smith, an English engineer in the late 1700s. Smith noticed that the kinds of fossils he found changed through a vertical succession of rock layers, and furthermore, that the same vertical changes in fossils occurred in different places.