Lecture 10

Time and Geology

Lecture OutlineI DefinitionsII Relative Time

A) Principlesi. Original Horizontalityii. Superpositioniii. Lateral Continuityiv. Cross-Cutting Relationshipsv. Inclusions

B) Unconformitiesi. Disconformityii. Angular Unconformityiii. Nonconformity

C) Correlationi. Physical Continuityii. Similarity of Rock Typesiii. Fossils

D) Standard Geologic Time Scale

Lecture 10i

Lecture OutlineIII Absolute Time

A) IsotopesB) Radioactive Decay

i. Types of Decaya) Alpha Emissionb) Beta Emissionc) Electron Capture

ii. Decay Systemsa) Uranium - 238

C) Isotopic DatingD) Uses of Isotopic Dating

i. Radiocarbon Datingii. Transport Tracingiii. Paleoclimatology

IV Using Relative and Absolute AgeV Conclusions

Lecture 10ii

Definitions

Lecture 10I

Uniformitarianismthe 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.

Definitions

Lecture 10I

•Group

•Formation

•Member

•Contact

Relative Time

Lecture 10II.A

Original Horizontality (Steno)

Superposition (Steno)

Lateral Continuity (Steno)

Cross-Cutting Relationships (Lyell)

Inclusions (Lyell)

Principles of Relative TimeOriginal Horizontality

Lecture 10II.A.i

Principles of Relative TimeSuperposition

Lecture 10II.A.ii

Principles of Relative TimeLateral Continuity

Lecture 10II.A.iii

Principles of Relative TimeCross-Cutting Relationships

Lecture 10II.A.iv

Principles of Relative TimeInclusions

Lecture 10II.A.v

Unconformities

Lecture 10II.B.1

unconformity - (1) a break or gap in the geologic record, such asas interruption in the normal sequence of deposition of sedimentary rocks, or a break between eroded metamorphicrocks and younger sedimentary strata. (2) the structural relationship between two groupsof rock that are not in normal succession.

conformity - (1) the relationship between adjacent sedimentarystrata that have been deposited in orderly sequence withlittle 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 erosionor nondeposition.

Unconformities

Lecture 10II.B.2

Disconformity

Angular Unconformity

Nonconformity

UnconformitiesDisconformity

Lecture 10II.B.i

an unconformity between beds that are parallel. The tendency is to apply the term to erosional breaks that arerepresented elsewhere by rockunits of at least formationalrank.

UnconformitiesAngular Unconformity

Lecture 10II.B.ii

an unconformity in whichyounger sediments rest upon the eroded surfaceof tilted or folded olderrocks.

UnconformitiesNonconformity

Lecture 10II.B.iii

an unconformity between stratified rocks above andunstratified igneous or metamorphic rocks below.

Correlation

Lecture 10II.C

Physical Continuity

Similarity of Rock Types

Fossils

CorrelationPhysical Continuity

Lecture 10II.C.i

CorrelationRock Type

Lecture 10II.C.ii

CorrelationFossil Assemblages

Lecture 10II.C.iii

Deep Time

Standard Geologic Time Scale

Lecture 10II.D

Divisions of TimeEon

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 Life"

Lecture 10II.D

The Standard Geologic Time ScaleChronostratigraphic Units

Chronologic Chronostratigraphic Unit _ _Unit Era Erathem Period System Epoch Series Age Stage Chron Zone

Absolute Time

Lecture 10III

Isotopes

Radioactive Decay

Absolute TimeIsotopes

Lecture 10III.A

isotopes - atoms of the same element that have different numbers of neutrons but the same number of protons

Absolute TimeRadioactive Decay Types

Lecture 10III.B.i

Half-Life

Radionuclides

Radioactive (parent)Radioactive (parent) Radiogenic (daughter)Radiogenic (daughter) Radioactive and RadiogenicRadioactive and Radiogenic CosmogenicCosmogenic

Radioactive Decay Systems

Radioactive Decay Systems238U 206Pb

Absolute TimeUses of Isotopic Dating

Lecture 10III.D

Radiocarbon Dating

Transport Tracing

Paleoclimatology

Half -life: 5,730 years

Effective Range: 100-40,000 years

Source Materials: Organic Matter

Uses: Radiocarbon Dating

Absolute TimeRadiocarbon Dating

Absolute TimeTransport Tracing

Lecture 10III.D.ii

Lecture 10III.D.iii

18O/16O (interglacial) < 18O/16O (glacial)

Absolute TimePaleoclimatology

Lecture 10IV

Using Absolute and Relative Dating