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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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Smith’s Map of England
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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 Dover’s 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 – 14 C, K-Ar, Rb-Sr,Uranium decay series
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CEE 437 Structural 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) –360 o Convention (120, 45) Right hand rule: dip 90 o 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
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