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Geologic Time Scale

Geologic Time Scale. Precambrian — Minimal fossil record Era, Period, Epoch Based on major changes — extinctions, mountain building events. Relative Time. Principle of Superposition Fossil Evidence Cross Cutting Relationships Unconformities Alteration Fracture Termination.

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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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