Time and Geology

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Lecture 10 Time and Geology
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Lecture Outline
I Definitions II Relative Time A) Principles
i. Original Horizontality ii. Superposition
iii. Lateral Continuity iv. Cross-Cutting
Relationships v. Inclusions B) Unconformities
i. Disconformity ii. Angular
Unconformity iii. Nonconformity C) Correlation
i. Physical Continuity ii. Similarity of
Rock Types iii. Fossils D) Standard Geologic
Time Scale
Lecture 10 i
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Lecture Outline
III Absolute Time A) Isotopes B) Radioactive
Decay i. Types of Decay a) Alpha
Emission b) Beta Emission c) Electron
Capture ii. Decay Systems a) Uranium -
238 C) Isotopic Dating D) Uses of Isotopic
Dating i. Radiocarbon Dating ii. Transport
Tracing iii. Paleoclimatology IV Using
Relative and Absolute Age V Conclusions
Lecture 10 ii
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Definitions
Uniformitarianism the fundamental principle that
geological processes and natural laws now
operating to modify the Earth's crust have acted
in much the same manner and with essentially the
same intensity throughout geologic time, and that
past geologic events can be explained by forces
observable today "The present is the key to the
past. The doctrine does not imply that all
change is at a uniform rate and does not exclude
minor local catastrophes.
Lecture 10 I
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Definitions

• Group
• Formation
• Member

• Contact

Lecture 10 I
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Relative Time

• Original Horizontality (Steno)
• Superposition (Steno)
• Lateral Continuity (Steno)
• Cross-Cutting Relationships (Lyell)
• Inclusions (Lyell)

Lecture 10 II.A
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Principles of Relative TimeOriginal Horizontality
Lecture 10 II.A.i
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Principles of Relative TimeSuperposition
Lecture 10 II.A.ii
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Principles of Relative TimeLateral Continuity
Lecture 10 II.A.iii
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Principles of Relative TimeCross-Cutting
Relationships
Lecture 10 II.A.iv
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Principles of Relative TimeInclusions
Lecture 10 II.A.v
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Unconformities
unconformity - (1) a break or gap in the geologic
record, such as
as interruption in the normal sequence of
deposition of sedimentary rocks, or a break
between eroded metamorphic rocks and younger
sedimentary strata. (2) the
structural relationship between two groups of
rock that are not in normal succession.
conformity - (1) the relationship between
adjacent sedimentary
strata that have been deposited in orderly
sequence with little or no evidence of time
lapse true stratigraphic continuity
(2) a surface that separates younger
strata from older ones, along which there is no
physical evidence of erosion or nondeposition.
Lecture 10 II.B.1
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Unconformities

• Disconformity
• Angular Unconformity
• Nonconformity

Lecture 10 II.B.2
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UnconformitiesDisconformity
an unconformity between beds that are parallel.
The tendency is to apply the term to erosional
breaks that are represented elsewhere by
rock units of at least formational rank.
Lecture 10 II.B.i
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UnconformitiesAngular Unconformity
an unconformity in which younger sediments rest
upon the eroded surface of tilted or folded
older rocks.
Lecture 10 II.B.ii
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UnconformitiesNonconformity
an unconformity between stratified rocks above
and unstratified igneous or metamorphic rocks
below.
Lecture 10 II.B.iii
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Correlation

• Physical Continuity
• Similarity of Rock Types
• Fossils

Lecture 10 II.C
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CorrelationPhysical Continuity
Lecture 10 II.C.i
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CorrelationRock Type
Lecture 10 II.C.ii
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CorrelationFossil Assemblages
Lecture 10 II.C.iii
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Deep Time
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Standard Geologic Time Scale

• Phanerozoic Eon -"Eon of Evident Life"
• Paleozoic Era -"Era of Old Life"
• Mesozoic Era -"Era of Middle Life"
• Cenozoic Era -"Era of Modern Life"

Divisions of Time Eon Era Period
Epoch Age Chron
Lecture 10 II.D
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The Standard Geologic Time Scale Chronostratigraph
ic Units
Chronologic Chronostratigraphic Unit
_ _Unit Era
Erathem Period
System Epoch Series
Age Stage Chron
Zone
Lecture 10 II.D
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Absolute Time

• Isotopes
• Radioactive Decay

Lecture 10 III
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Absolute TimeIsotopes
isotopes - atoms of the same element that
have different
numbers of neutrons but the same number of protons
Lecture 10 III.A
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Absolute TimeRadioactive Decay Types
Lecture 10 III.B.i
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Half-Life
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Radionuclides
Radioactive and Radiogenic
Cosmogenic
Radioactive (parent)
Radiogenic (daughter)
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Radioactive Decay Systems
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Radioactive Decay Systems 238U 206Pb
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Absolute TimeUses of Isotopic Dating

• Radiocarbon Dating
• Transport Tracing
• Paleoclimatology

Lecture 10 III.D
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Absolute TimeRadiocarbon Dating

• Half -life 5,730 years
• Effective Range 100-40,000 years
• Source Materials Organic Matter
• Uses Radiocarbon Dating

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Absolute TimeTransport Tracing
Lecture 10 III.D.ii
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Absolute TimePaleoclimatology
18O/16O (interglacial) lt 18O/16O
(glacial)
Lecture 10 III.D.iii
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Using Absolute and Relative Dating
Lecture 10 IV