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Geologic Time Scale

Explore the complex Geologic Time Scale, which spans from the Precambrian to the Cenozoic era, marking significant events in Earth's history, such as extinctions and mountain-building. Learn about the principles of relative and absolute time, including the significance of fossils, radiometric dating, and the structural geology of faults, folds, and deformation mechanisms. This overview covers essential concepts like brittle and ductile behavior, stress types, and geological maps, providing insights into engineering considerations and seismic hazards linked to geological features.

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Geologic Time Scale

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  1. Geologic Time Scale • Precambrian — Minimal fossil record • Era, Period, Epoch • Based on major changes — extinctions, mountain building events

  2. Relative Time • Principle of Superposition • Fossil Evidence • Cross Cutting Relationships • Unconformities • Alteration • Fracture Termination

  3. Siccar Point Unconformity

  4. Angular Unconformity – Santa Barbara

  5. Cross-cutting relationship - dike

  6. Smith’s Map of England

  7. 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

  8. 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 Dover’s cliffs

  9. 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

  10. 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

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

  12. CEE 437Structural Geology • World Stress • Brittle and Ductile Deformation • Faults and Joints • Folds

  13. 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

  14. Brittle Versus Ductile Behavior • Strain Rate Dependence • Non-elastic Deformation Mechanisms • recrystallization • lattice dislocations • pressure solution and redeposition

  15. World Stress Map

  16. Brittle Deformation • Extensile or Shear • Continuum of Joints and Faults • Faults as Strain Concentrators • Internal Structure of Faults

  17. In Situ Stress Measurement • Seismic data • First motions • Stress drops • Hydraulic Fracturing • Overcoring • Borehole Breakouts

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

  19. Fault Nomenclature • Hanging wall (overhead) • Footwall (underfoot) • Gouge • Damage Zone • Cataclasite • Mylonite

  20. Normal Fault, Death Valley

  21. http://darkwing.uoregon.edu/~millerm/slides.html

  22. Normal Fault, Canyonlands

  23. http://www.geo.cornell.edu/geology/classes/RWA/GS_326/photos/tf/DesertPk.jpghttp://www.geo.cornell.edu/geology/classes/RWA/GS_326/photos/tf/DesertPk.jpg

  24. Fault Gouge http://darkwing.uoregon.edu/~millerm/slides.html

  25. Sevier Thrust

  26. Keystone Thrust, Nevada http://darkwing.uoregon.edu/~millerm/slides.html

  27. Strike Slip Faults, Nevada http://darkwing.uoregon.edu/~millerm/slides.html

  28. Strike-Slip, San Andreas Fault, Carrizo Plain

  29. Engineering Concerns of Faults • Planes of Weakness • Sources of Seismic Hazard if Active • Significant Water Courses • Significant as Groundwater “Dams”

  30. 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

  31. Identifying Fold Types • Attitude of beds • Pattern of beds on geologic maps • Anticline — oldest at core • Syncline — youngest at core

  32. 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

  33. Ramp Fault, B.C.

  34. Recumbent Folds http://darkwing.uoregon.edu/~millerm/slides.html

  35. Fine-Scale Folding http://darkwing.uoregon.edu/~millerm/slides.html

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