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Geologic relative dating Lab. Which rock layer formed first? How do you know?. Relative Dating – Lab Which geologic event occurred first??. Relative Dating : Unraveling earth history by placing geologic events in chronological order “Which geologic process came first”?.

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Presentation Transcript
slide1

Geologic relative dating Lab

Which rock layer formed first?

How do you know?

Relative Dating – Lab

Which geologic event occurred first??

slide2

Relative Dating:

Unraveling earth history by

placing geologic events in

chronological order

“Which geologic process came first”?

NO actual numbers applied!

slide3

Objectives:

      • To observe exposures of rock and decipher
  • the geologic history
      • Use relative dating principles to unravel
      • geologic history

D

C

B

E

A

Igneous dike

Which layer was deposited first

A,B,C,D, or E??

slide4

Let’s unravel some geologic history from observations of

various formations and their contacts

Nicholas Steno – 1669 proposed the following relative

dating principles

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

Sediment input

C

B

A

slide6

The principle of Superposition

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

5

Youngest

4

3

2

1

Oldest

slide8

The principle of Inclusions

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

Rock body A

A

A

A

Older (rock A was there first)

Intrusion of pluton B

slide10

The principle of Cross Cutting relationships

    • Any geologic feature that cuts across another geologic
    • feature is younger

5

Is layer 5 older

or younger than

the intrusive

dike ??

4

3

2

6

1

slide11

A

B

C

Qtz-Asp Vn

Which dikes formed first?

slide12

Given this sequence of rock layers, “What’s

wrong with the timing of events????

A time of erosion

or non-deposition

“missing time”

Youngest

7

6

3

2

1

Oldest

slide13

The principle of Unconformities

    • Rock surface that represents a period of erosion or non deposition
    • Referred to “missing time”
    • Three major types of unconformities
      • Disconformity
      • Angular unconformity
      • Non-conformity

Disconformity – uncon in non-disturbed sedimentary

layers

Angular uncon – uncon lies between angled strata

and overlying horizontal strata

Non-conformity – sedimentary strata

overlies crystalline

rocks (ig and met)

Unconformity

slide14

Disconformity

Angular

Unconformity

Sedimentary rocks

Nonconformity

Xln rocks

slide15

Let’s apply the principles and unravel earth’s history

Which came first? -- start with oldest to youngest

I

Deposition of layers

G,H,I

youngest

H

G

Angular Uncon F

A

F

Tilting of layers

E,D,C,B,A

B

C

D

E

Deposition of layers

E,D,C,B,A

oldest

slide16

Rock symbols (rock legends)

Understand the various types

of rock (lithologic) symbols in

conjunction to the principles to

determine the geologic history

of an area.

emplacement

deposition

slide17

The 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.

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