EART 3 Geology of National Parks 10704

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EART 3- Geology of National Parks 1/07/04

• Outline
• National Parks of the Colorado Plateau
• The Grand Canyon- A Geologic View of Time
• Concepts
• Geologic Provinces
• Geologic History
• Rock Cycle
• Relative vs. Absolute Time

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Colorado Plateau Geologic Province

• Covered with flat lying sedimentary rocks
• Sedimentary rocks- composed of fragments of other
  rocks or derivatives of the ocean that have been
  deposited by water, wind or ice
• Rocks are uplifted between 1600-4300 m
  (5000-13000 ft) without being contorted
• Powerful rivers have cut deeply into the rocks
• Erosion in arid climate produced common
  topography of mesas, buttes, pinnacles and arches

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Flat lying sedimentary rocks
Bedding planes
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Colorado River cutting sedimentary section
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Colorado River cutting sedimentary rocks and
older metamorphic rocks
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Mesa Verde National Park
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Petrified Forest National Park
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Canyon de Chelly National Park
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Age of the Earth 4.5 by4500 my
Oldest rocks 4.0 by4000 my
Oldest rock in G C 2.0 by 2000 my
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Rock Cycle

• Sedimentary Rocks -composed of fragments of other
  rocks or derivatives of the ocean that have been
  deposited by water, wind or ice
• Igneous Rocks- Cool from magma underground
  (intrusive) or on the surface (volcanic)
• Metamorphic Rocks- Sedimentary or igneous rocks
  that change due to high temperatures and pressure
• Through various processes rock types may change
  throughout time

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Geologic View of Time

• Principle of Uniformitarianism- The present is
  the key to the past
• Principle of Original Horizontality- Sediments
  are laid down as flat layers
• Principle of Superposition- Oldest sedimentary
  rocks locate at the bottom with younger
  sedimentary rocks on top
• Unconformities- Breaks in time in the rock
  sequence caused by periods of non-deposition or
  erosion

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nonconformity
angular unconformity
disconformity
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Relative Time

• Rock Correlation- matches up rock units that look
  alike
• Fossil Correlation- matches up rock units that
  formed at the same time using similar fossils
  (index fossils)
• index Fossil- common, occur over large geographic
  areas and lived for a very short time
• Sex Pistols
• Tonya Harding
• Brian Bosworth
• AMC Pacer
• Vanilla Ice?

1977-1978
1994
1984-87
1975-80
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Fossil Correlation
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Absolute Time- Radioactive Decay

• Some isotopes of elements decay at known rates to
  other elements
• Isotopes- atoms with the same number of protons
  but different number of neutrons
• 235 Uranium (U) 207 Lead (Pb)
• parent daughter
• Half life- time for half of parent atoms to
  change to daughter
• Example
• Half life of 235U is 713 my . Start with 20
  atoms of 235U
• in 713 my (1 half life) there will be
• 10 atoms of 235U and 10 atoms of 207Pb
• in 1426 my (2 half lives) there will be

5 atoms of 235 U and 15 atoms of 207 Pb
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Cenozoic
66
Mesozoic
245
Paleozoic
570
Precambrian
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Geologic Time

• Precambrian Time 4.6-.57 by
• Atmosphere had little oxygen
• Mostly single celled and simple organisms
• Paleozoic Era .57 - .25 by (570-245 my)
• Rapid diversification of life
• Evolution of organisms with shells
• Invertebrates flourish
• Vertebrates appear
• Land plants appear
• MAJOR EXTINCTION OCCURS- 50 marine and 75 land
  organisms are wiped out

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Geologic Time

• Mesozoic Era 245-66 my
• Dinosaurs appear
• Mammals appear
• Reptiles flourish
• MAJOR EXTINCTION OCCURS
• Cenozoic Era 66- .0 my
• Mammals flourish