EESA06 Final Exam Ch11 Summary + 40 MCQ/T or F

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19 Apr 2012
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PHYSICAL GEOLOGY AND THE ENVIRONMENT
(2ND CANADIAN EDITION)
Chapter 11: Geologic Structures
Chapter Summary:
Tectonic forces result in deformation of the Earth's crust. Stress (force per unit area) is a measure
of the tectonic force and confining pressure acting on bedrock. Stress can be compressive,
tensional, or shearing. Strained (changed in size or shape) rock records past stresses, usually as
joints, faults, or folds.
A geologic map shows the structural characteristics of a region. Strike and dip symbols on
geologic maps indicate the attitudes of inclined surfaces such as bedding planes. The strike and
dip of a bedding surface indicate the relationship between the inclined plane and a horizontal
plane.
If rock layers bend (ductile behaviour) rather than break, they become folded. Rock layers are
folded into anticlines and synclines and recumbent folds. If the hinge line of a fold is not
horizontal, the fold is plunging. Older beds exposed in the core of a fold indicate an anticline,
whereas younger beds in the centre of the structure indicate a syncline. In places where folded
rock has been eroded to a plain, an anticline can usually be distinguished from a syncline by
whether the beds dip toward the centre (syncline) or away from the centre (anticline). Also, the
oldest rocks are found in the centre of an eroded anticline whereas the youngest rocks are found
in the centre or core of a syncline.
Fractures in rock are either joints or faults. A joint indicates that movement has not occurred on
either side of the fracture; displaced rock along a fracture indicates a fault. Dip-slip faults are
either normal or reverse, depending on the motion of the hanging-wall block relative to the
footwall block. The relative motion of the hanging wall is upward in a reverse fault and
downward in a normal fault. A reverse fault with a low angle of dip for the fault plane is a thrust
fault. Reverse faults accommodate horizontal shortening of the crust, whereas normal faults
accommodate horizontal stretching or extension.
In a strike-slip fault, which can be either left-lateral or right- lateral, horizontal movement
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PHYSICAL GEOLOGY AND THE ENVIRONMENT
(2ND CANADIAN EDITION)
parallel to the strike has occurred.
Questions:
1. Which of the following is a type of stress? (Page 277-278)
A. Shear
B. Compression
C. Tension
D. All of these are types of stress
2. The compass direction of a line formed by the intersection of an inclined plane and a
horizontal plane is called:
A. the cross-cutting angle
B. the intersection angle
C. strike
D. dip
3. Folding occurs when rocks behave as: (Page 282)
A. brittle solids
B. fluids
C. ductile solids
D. none of these
4. Anticlines:
A. form in rocks that are resistant to folding
B. form in rocks as a result of brittle deformation
C. are upward-arching folds
D. are downward-arching folds
5. Synclines:
A. are never observed in nature
B. are downward-arching folds
C. are upward-arching folds
D. form in rocks that are resistant to folding
6. In a syncline, the oldest rocks will be found: (Page 282-286)
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