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Physical Geology Review
the expanse of material is vast!
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Internal Structure of the Earthgranitic/basaltic
crust = 0-40 km; mantle = 40-2900 km; outer core (liquid) = 2900-5200 km; inner core = 5200-6400 km
from: www.usgs.gov
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Guidelines for Structural Analysis
• reference frame– law of original horizontality (rocks deposited
on nominally horizontal surfaces)– law of superposition (deposition of new layers
are on top of old layers)– stratigraphic continuity (deposits tend to be
continuous laterally, or discontinuous strata that lie in the same plane are equivalent in time)
• nature of contacts– stratigraphic (bedding or unconformities)– intrusive (igneous or sedimentary)– tectonic (fractures/faults)
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Basic Principles
• principle of superposition– younger rocks are deposited on top of older
rocks
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Basic Principles
• law of original horizontality– all sediments originally laid down in horizontal
layers
Grand Canyon, Arizona
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Basic Principles
• law of original horizontality– non-horizontal bedding implies some sort of
deformation
The Alps of Sisteron, France
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Interpreting Field Data
• strike and dip measurements• topography following geologic structure• geologic cross-sections
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“Undeformed”, horizontal rock
Cedar Point, UT
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Horizontal Bedding in Sedimentary Rocks
• original horizontality• lateral continuity• superposition
younger
older
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Strike and Dip
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Looking in strike direction,dip is angle from horizontal
arrow pointing down dip
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Interpreting Field Data
• strike and dip = attitude of planes (beds, fractures, ...)– strike is intersection of plane with horizontal– dip is angle between plane and horizontal
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Vertical BedsMiocene Monterey Fm., California coast
Laminated bedding with selective dolomitization (yellow beds)
1 meter
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Orientation of Planes (strike)
• 3d block diagram Horizontal is reference frame
Strike is intersection
between plane and horizontal
North is reference direction
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Orientation of Planes (dip)• vertical cross-section view
dip angle
Dip is inclination of plane from horizontal, measured in vertical plane perpendicular to strike
strike
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Folds and Faults
- folds are evidence of ductile rock deformation
- faults represent brittle rock deformation
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Monocline on the San Juan River, Utah
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Lateral Continuity (or lack thereof!)
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Faults
• vertical cross-section view
Hanging Wall
Footwall
dip angle
Fault
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Faults
• 3d block diagram
Footwall
Fault
Hanging Wall
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Footwall
Dip-Slip (Normal)
Hanging Wall
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Footwall
Dip-Slip (Normal)
Hanging Wall
horizontal stretching = extensionvertical thinning
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Footwall
Dip-Slip (Reverse)
Hanging Wall
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Footwall
Dip-Slip (Reverse)
Hanging Wall
horizontal shortening = contraction,vertical thickening
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Footwall
Strike-Slip
Hanging Wall
strike-slip faults are typically vertical, but they can be dipping like this one
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Footwall
Strike-Slip (right-lateral)
Hanging Wall
as you step across the fault, the block you are stepping onto moves to the right
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Footwall
Strike-Slip (left-lateral)
Hanging Wall
as you step across the fault, the block you are stepping onto moves to the left
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Footwall
Oblique-Slip
Hanging Wall
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Footwall
Oblique-Slip
Hanging Wall
both strike-slip and dip-slip
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Normal Fault with Basin Shaped Fold in Hanging Wall
Hanging Wall
FootWall
FaultPlane
Bedding
Slip vector
shear sense = normal
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Fault drag & shale smear
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Strike-slip fault and Drag folding
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Slickensides = shear
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Reverse Fault in Core
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A
B
Geologic Cross-section
A B
Cross-section view
Map view
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Fracture Types
• shear failure – faults– relative displacement is parallel to fracture face
= shearing mode
• tensile failure – joints, veins, dikes– a fracture with relative displacement
perpendicular to fracture face = opening mode
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Joint are “just” cracks….(looking at dip slopes)
orientation changes from bed to bed
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Joints(looking at bed scarps)
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A Joint filled with minerals = vein
Bristol Channel, UK Ouachita Mtns., Arkansas
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A “Joint” filled with magma = dike
Mt. Moran, Grand Tetons, WY
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Famous Fractures in the Movies
The Middle East?
from Transformers
hardly!
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How about New Mexico?
curving path to line up with earth stresses
volcanic source
volcanicsource
propagating dike
Volcanic Neck and Igneous
Dike:Shiprock dike
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Igneous Rock Features
from Press and Siever, Understanding Earth
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Other Geomorphic Features
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Glacial Moraine & U-shaped Valley
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Glacial Moraine
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Immature River – Steep, V-shaped Canyons
Yellowstone River
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Mature, meandering river (Yellowstone River)
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High energy rivers – heavy sediment load
braided stream
channel cut & fill,
graded bedding
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Alluvial fan
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Unconformities
• represent non-deposition or erosion• often indicate tectonic events or global sea level
change, laterally very continuous• types
– disconformity (parallel sed layers above and below, missing some time)
– nonconformity (sed rocks on top of igneous/metamorphic basement)
– angular unconformity (rocks above and below have different orientation)
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Angular Unconformity
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Disconformity
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Nonconformity
Cambrian Flathead ss on top of Precambrian granite
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