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