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Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 Lindsley-Griffin, 1999. Maroon Bells, Colorado
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Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

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Page 1: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Earth in TimeThe Rock Record and

Geologic Time

Earth in TimeThe Rock Record and

Geologic Time

GEOLOGY TODAY

Barbara W. MurckBrian J. Skinner

Chapter 3

N. Lindsley-Griffin, 1999.

Maroon Bells, Colorado

Page 2: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Original horizontality:

Sediments are deposited on a horizontal surface

Sedimentary rocks form in horizontal layers

Sedimentary rocks not horizontal were disturbed after they formed Folded sedimentary strata, Crete

Page 3: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Stratigraphic superposition:

Each layer of sedimentary rocks is deposited over the previous layer

Lower layers are always older than upper layers

Sandstone, limestone, and shale strata, Grand Canyon N.P., AZ

Page 4: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Cross-cutting relationships:

A rock unit is always older than any feature which cuts across or disrupts it.

Fractures cutting sandstone layers, Merseyside, UK

Page 5: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Cross-cutting relationships:

A rock unit is always older than any feature which cuts across or disrupts it.

Fractures cutting sandstone layers, Merseyside, UK

Page 6: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Correlation:Lateral continuity --

Strata can be traced from one location to another

Physical similarity --

Same characteristics

= same strata

Similar sequence of strata in two sections

= same sequenceCoal and sandstone strata, Badlands N.P., SD

Page 7: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Faunal succession:Each formation contains a unique fossil assemblage

Assemblages succeed one another in orderly, predictable sequence

Same everywhere in the world

In general, simpler organisms precede more complex ones in the same group

Dinosaur tracks

Page 8: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Faunal succession used for correlation:

Look for same fossils in same sequence of similar strata.

Fig. 3.6, p. 63

Page 9: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Absolute Age - PrinciplesAbsolute Age - Principles

© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999. All rights reserved

Radioactive Decay - Release of particles from nucleus

ALPHA EMISSION:Two protons + two neutronsMass - 4 Number - 2

BETA EMISSION:Neutron decays to a protonand gives off an electronMass - no change Number + 1

BETA CAPTURE:Proton captures electron andbecomes a neutronMass - no change Number - 1

Page 10: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Absolute Age - PrinciplesAbsolute Age - Principles

N. Lindsley-Griffin, 1999

Half-life: Time needed for the number of parent atoms to be reduced by one-half

At time zero, 100% P.A.

After one half-life, 50% P.A. and 50% D.A.

After two half-lives, 25% P.A. and 75% D.A.

Figure 3.12, p. 70

Page 11: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

© Houghton Mifflin 1998. All rights reserved

Carbon-14 Dating

Carbon-14 Dating

Neutrons in atmosphere change nitrogen-14 to carbon-14C-14 incorporated into tissue ofliving organismsRatio of C-14 to other C-isotopesremains constant in living tissueAt death, C-14 not replenished,ratio of C-14 to other C-isotopes decreasesAmount of C-14 remainingdetermines time since deathof organism

Page 12: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

N. Lindsley-Griffin, 1999

Proterozoic

Quaternary

Cretaceous

The Geologic Column[Fig. 3.8, p. 64]

Page 13: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

© Houghton Mifflin 1998. All rights reserved

Dating the Geologic Time Scale Dating the Geologic Time Scale

Sedimentary rocksnot easily dated radiometrically

Radiometric ages added to geologic timescale by:1. Cross-cutting relationships2. Bracketing

Page 14: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

N. Lindsley-Griffin, 1999

Unconformities:

Gaps in the rock record - recognized by an erosional surface

Signifies a major break in deposition

Columbia River Gorge, OR-WA

Page 15: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Relative Age - PrinciplesRelative Age - Principles

© Houghton Mifflin 1998. All rights reserved

Horizontal sedimentary rocks

Dike cuts strata - dike is younger

Fault cuts dike and strata - fault is youngest

Original horizontalitySuperpositionCross-cutting relationships Youngest

sedimentary rock

Oldestsedimentary rock

Page 16: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

© Houghton Mifflin 1998. All rights reserved

Dating the Geologic Time Scale Dating the Geologic Time Scale

Radiometric age of intrusion Y is 350 m.y.

Radiometric age of intrusion X is 400 m.y.

Devonian strata (B) must be older than 350 m.y. and younger than 400 m.y.

Mississippian strata are younger than 350 m.y.

Silurian strata are older than both Devonian and 400 m.y.

Radiometric dating and cross-cutting relationshipsbracket ages of sedimentary rocks

Page 17: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Angular unconformity - younger layers over tilted layers - Grand Canyon, AZ

N. Lindsley-Griffin, 1998

Page 18: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Angular unconformity - younger layers over tilted layers - Grand Canyon, AZ

N. Lindsley-Griffin, 1998

Page 19: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Disconformity Angular Unconformity

Time gap without angular relationship Time gap after folding, faulting

N. Lindsley-Griffin, 1998

Page 20: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Disconformity Angular Unconformity

Time gap without angular relationship Time gap after folding, faulting

N. Lindsley-Griffin, 1998

Page 21: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

“Baked zone” - soil formed on older lava flow before being covered and cooked by a

new lava flow - DisconformityN. Lindsley-Griffin, 1998

Page 22: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

“Baked zone” - soil formed on older lava flow before being covered and cooked by a

new lava flow - DisconformityN. Lindsley-Griffin, 1998

Page 23: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Nonconformity - sedimentary rocks over crystalline (metamorphic or igneous) rocks

N. Lindsley-Griffin, 1998

Page 24: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Nonconformity - sedimentary rocks over crystalline (metamorphic or igneous) rocks

N. Lindsley-Griffin, 1998

Page 25: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Nonconformity - sedimentary gravels over garnet schist. What is the history of this outcrop?

N. Lindsley-Griffin, 1998

Page 26: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Nonconformity - sedimentary gravels over garnet schist. What is the history of this outcrop?

N. Lindsley-Griffin, 1998

Page 27: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Cross-cutting relationships: dike cutting gneiss is youngerN. Lindsley-Griffin, 1998

Page 28: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Cross-cutting relationships: dike cutting gneiss is youngerN. Lindsley-Griffin, 1998

Page 29: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Cross cutting relationships: what is the sequence of events in this folded marble with two dikes?

N. Lindsley-Griffin, 1998

Page 30: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Cross cutting relationships: what is the sequence of events in this folded marble with two dikes?

N. Lindsley-Griffin, 1998

Page 31: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Superposition

Disconformity

Original horizontality

Angular unconformity

Cross-cutting relationships

Nonconformity

Grand Canyon FormationsGrand Canyon Formations

© Houghton Mifflin 1998. All rights reserved

Page 32: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Grand Canyon FormationsGrand Canyon Formations

© Houghton Mifflin 1998. All rights reserved

Sequence of events based on geology of the Inner Gorge

1.Deposition of shale in marine environment

2. Metamorphism of shale into Vishnu schist

3. Intrusion by Zoroaster granite

4. Erosion to sea level, unconformity surface

5. Deposition of Grand Canyon Supergroup

6. Faulting 7. Erosion of fault blocks, deposition of Tapeats sandstone

Page 33: Earth in Time The Rock Record and Geologic Time GEOLOGY TODAY Barbara W. Murck Brian J. Skinner Chapter 3 N. Lindsley-Griffin, 1999. Maroon Bells, Colorado.

Geologic Time - SummaryGeologic Time - Summary

N. Lindsley-Griffin, 1999

Relative Age -- whether a particular rock or feature is older or younger than another

Absolute Age -- the age of a rock in years (m.y. = millions of years)

Geologic Column -- shows succession of all known strata, in chronological order, based on fossils and other relative ages