geologic time scale precambrian — minimal fossil record era, period, epoch based on major changes...
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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
Siccar Point Unconformity
Angular Unconformity – Santa Barbara
Cross-cutting relationship - dike
Smith’s Map of England
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
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
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
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
Absolute Time
• Basis on radiometric dating (see Rahn chapter 1)
• Common dating tools– 14C, K-Ar, Rb-Sr,Uranium decay series
CEE 437Structural Geology
• World Stress
• Brittle and Ductile Deformation
• Faults and Joints
• Folds
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
Brittle Versus Ductile Behavior
• Strain Rate Dependence
• Non-elastic Deformation Mechanisms– recrystallization– lattice dislocations– pressure solution and redeposition
World Stress Map
Brittle Deformation
• Extensile or Shear
• Continuum of Joints and Faults
• Faults as Strain Concentrators
• Internal Structure of Faults
In Situ Stress Measurement
• Seismic data– First motions– Stress drops
• Hydraulic Fracturing
• Overcoring
• Borehole Breakouts
Fault Types
• Normal — Extensile Deformation– Hanging Wall down– Horsts and Grabens
• Reverse — Compressive Deformation– Hanging Wall up– Thrust Faults
• Strike-slip – Mostly transform faults
Fault Nomenclature
• Hanging wall (overhead)
• Footwall (underfoot)
• Gouge
• Damage Zone
• Cataclasite
• Mylonite
Normal Fault, Death Valley
http://darkwing.uoregon.edu/~millerm/slides.html
Normal Fault, Canyonlands
http://www.geo.cornell.edu/geology/classes/RWA/GS_326/photos/tf/DesertPk.jpg
Fault Gouge
http://darkwing.uoregon.edu/~millerm/slides.html
Sevier Thrust
Keystone Thrust, Nevada
http://darkwing.uoregon.edu/~millerm/slides.html
Strike Slip Faults, Nevada
http://darkwing.uoregon.edu/~millerm/slides.html
Strike-Slip, San Andreas Fault, Carrizo Plain
Engineering Concerns of Faults
• Planes of Weakness
• Sources of Seismic Hazard if Active
• Significant Water Courses
• Significant as Groundwater “Dams”
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
Identifying Fold Types
• Attitude of beds
• Pattern of beds on geologic maps
• Anticline — oldest at core
• Syncline — youngest at core
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
Ramp Fault, B.C.
Recumbent Folds
http://darkwing.uoregon.edu/~millerm/slides.html
Fine-Scale Folding
http://darkwing.uoregon.edu/~millerm/slides.html