Geologic Time Earth’s History. Determining Earth’s History Must determine sequence of events...
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Transcript of Geologic Time Earth’s History. Determining Earth’s History Must determine sequence of events...
Geologic TimeGeologic Time
Earth’s HistoryEarth’s History
Determining Earth’s HistoryDetermining Earth’s History
Must determine Must determine sequence of eventssequence of events
To establish To establish chronological chronological framework use:framework use: Relative AgeRelative Age Absolute AgeAbsolute Age
Dating – 2 typesDating – 2 types• Relative DatingRelative Dating
•Absolute Dating
– Place rocks and events in sequence of formation
– Specify actual number of years that have passed since the event occurred
Principles of Relative DatingPrinciples of Relative Dating
• Law of Superposition—StenoLaw of Superposition—Steno• Principle of Original Horizontality –Principle of Original Horizontality –StenoSteno
• Principle of Lateral Continuity– StenoPrinciple of Lateral Continuity– Steno• Principle of Cross-Cutting Principle of Cross-Cutting Relationships—HuttonRelationships—Hutton
• Principle of InclusionsPrinciple of Inclusions• Principle of Faunal Succession—Principle of Faunal Succession—William SmithWilliam Smith
• Principle of Baked ContactsPrinciple of Baked Contacts
Law of SuperpositionLaw of Superposition In an In an undisturbedundisturbed section, each bed is section, each bed is
younger than the bed below it.younger than the bed below it.– map formations, beds, etc.
Disturbed SectionsDisturbed Sections
http://ceed.utpb.edu/geology-resources/west-texas-geology/folds/http://facweb.bhc.edu/academics/science/harwoodr/geol101/study/structur.htm
Principle of Original Principle of Original HorizontalityHorizontality
Sedimentary layers are mostly deposited Sedimentary layers are mostly deposited horizontallyhorizontally
Which way is up? Or in which Which way is up? Or in which direction are beds younger?direction are beds younger?
Key to establishing Key to establishing sequence of events is to sequence of events is to know which way is up.know which way is up.
Vertical beds (quartzite, Vertical beds (quartzite, limestone, and shale) in limestone, and shale) in mouth of Sheep Creek mouth of Sheep Creek Canyon, probably sec. Canyon, probably sec. 5, T. 17 N., R. 6 E., 22 5, T. 17 N., R. 6 E., 22 miles northwest of miles northwest of Silver Lake, Crucero Silver Lake, Crucero Quadrangle, San Quadrangle, San Bernardino County, Bernardino County, California. October 16, California. October 16, 1917. - ID. Thompson, 1917. - ID. Thompson, D.G. 99 - tdg00099 - D.G. 99 - tdg00099 - U.S. Geological SurveyU.S. Geological Survey
Principle of Lateral ContinuityPrinciple of Lateral Continuity
Layers of sediments extend laterally Layers of sediments extend laterally until pinches out (terminates)until pinches out (terminates)
Principle of Cross-Cutting Principle of Cross-Cutting RelationshipsRelationships
• Faults and intrusions are younger than the rocks Faults and intrusions are younger than the rocks they cut throughthey cut through
Principle of Faunal SuccessionPrinciple of Faunal Succession
Evolution is Evolution is irreversibleirreversible
Therefore, can use Therefore, can use fossils to establish fossils to establish order of eventsorder of events
Principle of InclusionsPrinciple of Inclusions
• Fragments of one rock unit that have been enclosed within Fragments of one rock unit that have been enclosed within another are olderanother are older
In each diagram, which inclusion is younger? Older?
Baked ContactsBaked Contacts
Intrusions bake rocks around itIntrusions bake rocks around it
Relative DatingRelative Dating
Youngest G A
BCFD
Oldest E
Place these rocks from youngest to oldest
Conformable and Unconformable Conformable and Unconformable BedsBeds
• Conformable BedsConformable Beds• Beds that have not been disturbedBeds that have not been disturbed• Image of Permian-Jurassic sequence, Colorado Image of Permian-Jurassic sequence, Colorado
PlateauPlateau
UncomformitiesUncomformities
• Substantial break or gap in the rock record• All geologic history not evident
• But part of record remainsBut part of record remains• Have uplift and erosion, unconformity produced
• 3 types of unconformites• AngularAngular• Disconformity• Nonconformity
Angular UnconformityAngular Unconformity Tilted rocks are overlain by flat-lying rocksTilted rocks are overlain by flat-lying rocks
Siccar Point, England
DisconformityDisconformity
• Beds are parallel Beds are parallel relative to each relative to each other but there is other but there is a break in a break in sequencesequence
• Implies a cessation of sedimentation or erosion, but no tilting
• Hard to recognize
NonconformityNonconformity
Sedimentary layers overlie igneous or Sedimentary layers overlie igneous or metamorphic layersmetamorphic layers
UnconformitiesUnconformities
1. Surface 1 is an example of ? Nonconformity2. Surface 2 is an example of ? Angular unconformity3. Surface 3 and 4? Disconformity4. Granite is _________ than the Schist. Younger
Question: Answer:
1
2
3
4
http://facweb.bhc.edu/academics/science/harwoodr/Geol101/Study/Images/D041-551.jpg