Lecture 10
Time and Geology
Lecture Outline
I
II
Definitions
Relative Time
A)
Principles
i.
ii.
iii.
iv.
v.
B)
Unconformities
i.
ii.
iii.
C)
Disconformity
Angular Unconformity
Nonconformity
Correlation
i.
ii.
iii.
D)
Original Horizontality
Superposition
Lateral Continuity
Cross-Cutting Relationships
Inclusions
Physical Continuity
Similarity of Rock Types
Fossils
Standard Geologic Time Scale
Lecture 10
i
III
Absolute Time
Lecture Outline
A) Isotopes
B) Radioactive Decay
i.
ii.
Types of Decay
a) Alpha Emission
b) Beta Emission
c) Electron Capture
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
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
Definitions
Group
•
Formation
•
Member
•
Contact
•
Lecture 10
I
Relative Time
Original Horizontality (Steno)
Superposition (Steno)
Lateral Continuity (Steno)
Cross-Cutting Relationships (Lyell)
Inclusions (Lyell)
Lecture 10
II.A
Principles of Relative Time
Original Horizontality
Lecture 10
II.A.i
Principles of Relative Time
Superposition
Lecture 10
II.A.ii
Principles of Relative Time
Lateral Continuity
Lecture 10
II.A.iii
Principles of Relative Time
Cross-Cutting Relationships
Lecture 10
II.A.iv
Principles of Relative Time
Inclusions
Lecture 10
II.A.v
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
Unconformities
Disconformity
Angular Unconformity
Nonconformity
Lecture 10
II.B.2
Unconformities
Disconformity
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
Unconformities
Angular Unconformity
an unconformity in which
younger sediments rest
upon the eroded surface
of tilted or folded older
rocks.
Lecture 10
II.B.ii
Unconformities
Nonconformity
an unconformity between
stratified rocks above and
unstratified igneous or
metamorphic rocks below.
Lecture 10
II.B.iii
Correlation
Physical Continuity
Similarity of Rock Types
Fossils
Lecture 10
II.C
Correlation
Physical Continuity
Lecture 10
II.C.i
Correlation
Rock Type
Lecture 10
II.C.ii
Correlation
Fossil Assemblages
Lecture 10
II.C.iii
Deep Time
Standard Geologic Time Scale
Divisions of Time
Eon
Era
Period
Epoch
Age
Chron
Phanerozoic Eon -"Eon of Evident Life"
Paleozoic Era
-"Era of Old Life"
Mesozoic Era
-"Era of Middle Life"
Cenozoic Era
-"Era of Modern Lif
Lecture 10
II.D
Chronologic
Unit
Era
Period
Epoch
Age
Chron
The Standard Geologic Time Scale
Chronostratigraphic Units
Chronostratigraphic
_
_Unit
Erathem
System
Series
Stage
Zone
Lecture 10
II.D
Absolute Time
Isotopes
Radioactive Decay
Lecture 10
III
Absolute Time
Isotopes
isotopes - atoms of the same element that have different
numbers of neutrons but the same number of protons
Lecture 10
III.A
Absolute Time
Radioactive Decay Types
Lecture 10
III.B.i
Half-Life
Radionuclides
Radioactive (parent)
Radiogenic (daughter)
Radioactive and Radiogenic
Cosmogenic
Radioactive Decay Systems
Radioactive Decay Systems
238U
206Pb
Absolute Time
Uses of Isotopic Dating
Radiocarbon Dating
Transport Tracing
Paleoclimatology
Lecture 10
III.D
Absolute Time
Radiocarbon Dating
Half -life: 5,730 years
Effective Range: 100-40,000 years
Source Materials: Organic Matter
Uses: Radiocarbon Dating
Absolute Time
Transport Tracing
Lecture 10
III.D.ii
Absolute Time
Paleoclimatology
18O/16O
(interglacial)
<
18O/16O
(glacial)
Lecture 10
III.D.iii
Using Absolute and Relative Dating
Lecture 10
IV