Geologic Time Scale

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Geologic Time Scale

• Precambrian Minimal fossil record
• Era, Period, Epoch
• Based on major changes extinctions, mountain
  building events

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Relative Time

• Principle of Superposition
• Fossil Evidence
• Cross Cutting Relationships
• Unconformities
• Alteration
• Fracture Termination

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Siccar Point Unconformity
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Angular Unconformity Santa Barbara
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Cross-cutting relationship - dike
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Smiths Map of England
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(No Transcript)
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Paleozoic (Old Life) Brachiopods, Trilobites,
Fish

• Periods based on English Geology
• Cambrian for Latin Wales
• Ordovician and Silurian for ancient Welsh Tribes
• Devonian for Devon
• Carboniferous for Coal Measures (also
  Mississippian and Pennsylvanian in US)
• Permian for Perm Basin in Ukraine

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Mesozoic (Middle Life) Ammonites, Dinosaurs

• Triassic based on distinctive three-layer
  stratigraphy in southern Germany
• Jurassic based on Jura Mountains in France and
  Switzerland
• Cretaceous (Latin for Chalk) based on chalk unit
  that forms Dovers cliffs

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Cenozoic (Recent Life) Mammals, Modern marine
fauna (foraminifera)

• Periods are Tertiary (before Ice Ages) and
  Quaternary (ice ages)
• Primary and secondary have been long replaces
• Rocks of western Washington are Tertiary and
  Quaternary

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Age of the Earth

• Kelvin and a basis in heat flow (set at 20
  million years)
• Problem of fitting all of evolution in this time
• Rutherford and the introduction radioactive decay
• Added a head source, pushed ages back to 4.5
  billion years

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Absolute Time

• Basis on radiometric dating (see Rahn chapter 1)
• Common dating tools
• 14C, K-Ar, Rb-Sr,Uranium decay series

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CEE 437Structural Geology

• World Stress
• Brittle and Ductile Deformation
• Faults and Joints
• Folds

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Representing a Plane

• Strike and Dip
• Quadrant Convention (N 60 E, 45 SE)
• 360o Convention (120, 45)
• Right hand rule dip 90o clockwise of strike)
• Pole trend and plunge
• Dip vector
• does not discriminate strike of vertical planes

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Brittle Versus Ductile Behavior

• Strain Rate Dependence
• Non-elastic Deformation Mechanisms
• recrystallization
• lattice dislocations
• pressure solution and redeposition

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World Stress Map
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Brittle Deformation

• Extensile or Shear
• Continuum of Joints and Faults
• Faults as Strain Concentrators
• Internal Structure of Faults

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In Situ Stress Measurement

• Seismic data
• First motions
• Stress drops
• Hydraulic Fracturing
• Overcoring
• Borehole Breakouts

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Fault Types

• Normal Extensile Deformation
• Hanging Wall down
• Horsts and Grabens
• Reverse Compressive Deformation
• Hanging Wall up
• Thrust Faults
• Strike-slip
• Mostly transform faults

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Fault Nomenclature

• Hanging wall (overhead)
• Footwall (underfoot)
• Gouge
• Damage Zone
• Cataclasite
• Mylonite

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Normal Fault, Death Valley
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http//darkwing.uoregon.edu/millerm/slides.html
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Normal Fault, Canyonlands
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http//www.geo.cornell.edu/geology/classes/RWA/GS_
326/photos/tf/DesertPk.jpg
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Fault Gouge
http//darkwing.uoregon.edu/millerm/slides.html
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Sevier Thrust
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Keystone Thrust, Nevada
http//darkwing.uoregon.edu/millerm/slides.html
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Strike Slip Faults, Nevada
http//darkwing.uoregon.edu/millerm/slides.html
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Strike-Slip, San Andreas Fault, Carrizo Plain
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Engineering Concerns of Faults

• Planes of Weakness
• Sources of Seismic Hazard if Active
• Significant Water Courses
• Significant as Groundwater Dams

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Folds

• Anticline
• Concave down or oldest beds at core
• Syncline
• Concave up or youngest beds at core
• Overturned and Recumbent Folds
• Fold Terms
• Hinge, Axis

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Identifying Fold Types

• Attitude of beds
• Pattern of beds on geologic maps
• Anticline oldest at core
• Syncline youngest at core

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Engineering Concerns of Folds

• Means of Extrapolating Bed Locations
• Fracturing related to folding
• Favorable or non-favorable orientations of beds
  to engineered structures or slopes

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Ramp Fault, B.C.
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Recumbent Folds
http//darkwing.uoregon.edu/millerm/slides.html
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Fine-Scale Folding
http//darkwing.uoregon.edu/millerm/slides.html