Don Barrie, Geoscience Educator

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Chapter 14—Sediment and Sedimentary Rocks


1. What conditions of climate, weathering rate, and erosion rate could lead to a feldspar-rich sandstone? Explain your answer.

Arid (dry) climate, slow chemical weathering rate, and rapid erosion rate could lead to a feldspar-rich sandstone because the feldspars would be unlikely under such conditions to chemically weather to clay before becoming incorporated into a sandstone.

3. What do mud cracks tell us about the environment of deposition of a sedimentary rock

Mud cracks tell us that the depositional environment was exposed above water and probably characterized by dry, evaporative conditions.

5. List the detrital sediment particles in order of decreasing grain size.

Gravel (made up of boulders, cobbles, and pebbles), sand, silt, clay.

6. How does a sedimentary breccia differ from appearance and origin from a conglomerate?

A sedimentary breccia consists of large, angular fragments whereas conglomerate consists of large, rounded fragments. Sedimentary breccias consist of rock fragments that haven’t been transported as far as those in a conglomerate.

9. What is the origin of coal?

Coal originates as plant matter is rapidly buried and consolidated.

12. Name the three most common sedimentary rocks.

Limestone, sandstone, and shale.

17. D 18. B 19. B 20. D 21. B 22. B 23. A

Chapter 15—Metamorphism and Metamorphic Rocks

3. How do regional metamorphic rock differ in texture from contact metamorphic rocks?

Regional metamorphic rocks are typically foliated whereas contact metamorphic rocks are not.

5. How would you distinguish (a) gneiss from schist, (b) slate from phyllite, (c) quartzite from marble, (d) granite from gneiss?

a. Gneiss exhibits visible (compositional) banding whereas schist does not. Schist is usually strongly foliated, showing visible alignment of mica minerals, whereas the micas in gneiss, if present, may not be as strongly aligned.

b. Phyllite exhibits a wavy foliation and a satin sheen, whereas slate is typically dull and breaks along flat, parallel planes.

c. Quartzite (composed on the mineral, quartz) is harder than marble. Marble (composed on calcite) fizzes in hydrochloric acid.

d. Granite does not display visible banding, whereas gneiss does.

6.Why is an edifice built with blocks of quartzite more durable than one build of marble blocks?

Marble is composed of calcite and therefore easily dissolved, particularly in humid climates, whereas quartzite, composed of quartz, is not.

7. D 9. B 10. A 11. C 12. B 13. C 14. C 15. D 18. D

Chapter 8—Time and Geology

2. See entire question...How many half-lives have gone by? How old is the rock?

5 half-lives have gone by; the rock is 600,000 years old. If the rock originally possessed 8 grams of radioactive isotope X (half life = 120,000 yrs), then after 1 half-life it would posses 4 grams; after 2 half-lives it would posses 2 grams; after 3 half-lives it would possess 1 gram; after 4 half-lives it would possess ½ gram, and after 5 half- lives it would possess ¼ gram. So our rock is 5 half-lives old; 5 * 120,000 = 600,000 years old.

6. C 7. B 8. A 9. D 10. A 11. B 12. A 13. E 14. D 16. D 18. B 19. A

Chapter 7—Earthquakes

2. What causes earthquakes?

Fault rupture associated with the sudden release of energy is the direct cause of most earthquakes.

3. Compare and contrast the concepts of intensity and magnitude of earthquakes. Intensity and magnitude are both ways of measuring the size of an earthquake.

Whereas intensity measures earthquake size in terms of damage caused, magnitude measures earthquake size in terms of ground motion and energy released. Intensity is a descriptive way of summarizing the damage caused by an earthquake, whereas magnitude is numerical measure of ground motion and energy release.

4. Name and describe the various types of seismic waves.

P-waves: body waves; travel in Earth’s interior; propagate via compression; fastest type of wave; can travel through solids, liquids, and gases.
S-waves: body waves; travel in Earth’s interior; propagate via shear; can’t travel through liquids or gases.
Love waves: surface waves; travel at/near Earth’s surface; propagate by sideways shearing, like S waves but with no vertical displacement.
Rayleigh waves: surface waves; gravel at/near Earth’s surface; propagate via a rolling motion similar to a water wave, causing the ground to move in an elliptical path.
9. Describe several ways that earthquakes cause damage.

Fault rupture—rapid displacement of the ground along a fault.
Strong ground shaking—associated with the propagation of seismic waves.
Mass wasting—slope failure associated with strong ground shaking.
Liqefaction—ground failure caused by the transformation of loose, water-saturated sediments to a fluid during an earthquake.
Tsunami—powerful, destructive water waves generated by vertical motion of the seafloor sometimes produced during an earthquake.
10. How do earthquakes cause tsunami?

Earthquakes cause tsunami as fault movement associated with an oceanic earthquake causes rapid, vertical changes on the sea floor. This results in a large vertical displacement of ocean water, which in turn, creates a tsunami, as the displaced water propagates outward like large ripples on a pond.

12. C 13. A 14. A 15. C 16. B 17. D 18. A 19. D 20. A

Chapter 6—Geologic Structures

1. Most anticlines have both limbs dipping away from their hinge lines. For which kind of fold is this not the case.

Syncline—a downfold in which both limbs dip toward the hinge line.

2.Skip

3. On a geologic map, if no cross sections are available, how could you distinguish an anticline from a syncline?

One would still see a reversal of dip direction across the fold hinge, as indicated by strike and dip symbols. Also, an eroded anticline will expose the oldest rock in the center (hinge region) of the fold, whereas a syncline will expose the youngest rock in the center (hinge region) of the fold.

4. If you locate a dip-slip fault while doing field work, what kind of evidence would you look for to determine whether the fault is normal or reverse?

First, identify the hanging wall and the footwall. If the hanging wall has moved UP relative to the footwall, it’s a reverse fault; however, if the hanging wall has moved DOWN relative to the footwall, it’s a normal fault.

9. D 11. A 12. C 13. D 14. C 15. E 16. B 17. B 18. B 19. B