GLY 155 Introduction to Physical Geology, W. Altermann
©
Press & Siever, 1995
GLY 155 Introduction to Physical Geology, W. Altermann
©
compressive
forces
Compressive forces cause
folding and faulting.
faults
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Uplift is followed by erosion, which creates
new horizontal surface.
GLY 155 Introduction to Physical Geology, W. Altermann
©
lava flows
Volcanic eruptions cover
the surface with lava flows.
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GLY 155 Introduction to Physical Geology, W. Altermann
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Tensional forces cause
normal faults, creating
down-dropped
blocks and
breaking up
earlier features.
tensional forces
normal faults
GLY 155 Introduction to Physical Geology, W. Altermann
©
Fish River Canyon, Namibia
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GLY 155 Introduction to Physical Geology, W. Altermann
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Bedding and unconformities:
All sedimentary rocks are characterized through bedding:
•The bedding originates from alternating conditions of deposition in
time.
•The layers of sediment are deposited horizontally
The law of layer superposition:
GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Missing bed B - deposited and eroded or not deposited?
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Bed D is pinching out to the right and has not been deposited in the
right profile
GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Reconstruction of relative time events from bedding and conformity relationships
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Two erosional
unconformities
in the Grand
Canyon
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Reconstruction of relative time events from bedding and conformity relationships
GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Paraconformity
Disconformity
Nonconformity
Unconformities:
Time gaps in sedimentary record
Paraconformity: Time of non deposition without noticeable
erosion
Disconformity: Time of erosion within a depositional sequence
Angular unconformity
Nonconformity: Time of exhumation and erosion of a much
older igneous rock
Angular unconformity: Time of exhumation and erosion of a
folded or tilted rock sequence
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GLY 155 Introduction to Physical Geology, W. Altermann
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Old
Oldland
landsurface
surface-Erosional
Erosionalsurface
surface
Transgression conglomerate
GLY 155 Introduction to Physical Geology, W. Altermann
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Transgression conglomerate on the
Sardic unconformity
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GLY 155 Introduction to Physical Geology, W. Altermann
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Bedding and unconformities:
Reconstruction of relative time events from bedding and conformity relationships
GLY 155 Introduction to Physical Geology, W. Altermann
©
Bedding and unconformities:
Sequence of events:
1. Sedimentation of the sequence of A to G
2. Folding and faulting of A to G
3. Intrusion of a granite into A to G
4. Exhumation and erosion of A to G and of the granit
5. Deposition of X to Z as horizontal layers
6. Tilting of the entire system to the E (right)
7. Intrusion of a vertical dyke into the granite and A to G
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GLY 155 Introduction to Physical Geology, W. Altermann
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Chapter 7:
DeformationModification of
Rocks by Folding
and Fracturing
GLY 155 Introduction to Physical Geology, W. Altermann
©
Plate Tectonic Forces
Deformation
tensional forces
compressive forces
shearing forces
Outcrop – basic source of geologic
information in the field
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GLY 155 Introduction to Physical Geology, W. Altermann
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Mapping Geologic Structure
GLY 155 Introduction to Physical Geology, W. Altermann
©
Mapping Geologic Structure
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Mapping Geologic Structure
GLY 155 Introduction to Physical Geology, W. Altermann
©
Mapping Geologic Structure
W
S
Dip
N
n
ctio
dire
45°
Strik
e
Dip
angle
direc
tion
E
N
W
S
45°
Dip angle
E
Water trickles down
slope parallel to dip.
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Outcrop – basic
source of geologic
information in the
field
Dinosaur Ridge,
located west of Denver,
Colorado.
GLY 155 Introduction to Physical Geology, W. Altermann
©
Mapping Geologic Structure
Geologic maps
geologic maps represent the rock formations exposed
at Earth’s surface
A common scale for geologic maps is 1:25000
Geologic cross sections
geologic cross sections – diagrams showing the
features that would be visible if vertical slices were
made through part of the crust
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GLY 155 Introduction to Physical Geology, W. Altermann
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GLY 155 Introduction to Physical Geology, W. Altermann
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Basic Deformation Structures
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Example
of a
strikeslip fault
GLY 155 Introduction to Physical Geology, W. Altermann
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Basic Deformation Structures
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GLY 155 Introduction to Physical Geology, W. Altermann
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GLY 155 Introduction to Physical Geology, W. Altermann
©
Basic Deformation Structures
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GLY 155 Introduction to Physical Geology, W. Altermann
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GLY 155 Introduction to Physical Geology, W. Altermann
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joints
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GLY 155 Introduction to Physical Geology, W. Altermann
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Styles of Continental Deformation
GLY 155 Introduction to Physical Geology, W. Altermann
©
Styles of Continental Deformation
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GLY 155 Introduction to Physical Geology, W. Altermann
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Styles of Continental Deformation
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GLY 155 Introduction to Physical Geology, W. Altermann
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Example
of
tensional
tectonics
GLY 155 Introduction to Physical Geology, W. Altermann
©
Example of
compressive
tectonics
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GLY 155 Introduction to Physical Geology, W. Altermann
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Example
of
shearing
tectonics
GLY 155 Introduction to Physical Geology, W. Altermann
©
Thought questions for this chapter
In what sense is a geologic map a scientific model of the surface
surface geology? Is it fair to
say that geologic cross sections in combination with a geologic map describe a
scientific model of a threethree-dimensional geologic structure?
Why is it correct to say that “largelarge-scale geologic structures should be represented on
smallscale
geologic
maps”
”
?
How
large a piece of paper would be required to make a
small
maps
map of the entire U.S. Rocky Mountains at 1;24,000 scale?
Can you explain the geologic story in Exercise 6 (Understanding Earth, p. 188, ) in
terms of plate tectonics?
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GLY 155 Introduction to Physical Geology, W. Altermann
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Thought questions for this chapter
The submerged margin of a continent has a thick layer of sediments
sediments
overlying metamorphic basement rocks. That continental margin
collides with another continental mass, and the compressive forces
forces
deform it into a fold and thrust belt. During the deformation, which of
the following geologic formations would be likely to behave as brittle
brittle
materials and which as ductile materials?
(a) sedimentary formations in the upper few km
(b) metamorphic basement rocks at depths of 55-15 km
(c) lower crustal rocks below 20 km
In which of these layers would you expect earthquakes?
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