CHAPTER 6 Sedimentary Rocks
174
G I V E I T S O M E T H O U G H T
Dust collecting on furniture is an everyday example of a sedimentary
process. Provide another example of a sedimentary process that
might be observed in or around where you live.
Discuss two reasons sedimentary rocks are more likely to contain
fossils than igneous rocks.
Imagine you are studying sedimentary deposits in an abandoned
river channel. You see layers of well-sorted sand alternating with
coarser-grained, poorly sorted material consisting of sand, gravel,
and rock fragments. How would you interpret the history of this
river channel based on these layers of sediment? What might the
layers indicate about possible changes in climate conditions and the
flow of water in the river in the past?
If you hiked to a mountain peak and found limestone at the top,
what would that indicate about the likely geologic history of the
rock atop the mountain?
In which of the environments illustrated in Figure 6.18 would you
expect to find:
a. A deposit consisting of several beds in which sediment sizes in
each bed decrease from bottom to top.
b. An evaporite deposit.
c. A well-sorted sand deposit.
d. A deposit that includes a high percentage of partially decomposed plant material.
5
4
3
2
1
While on a field trip with your geology class, you stop at an outcrop
of sandstone. An examination with a hand lens shows that the sandstone is poorly sorted and rich in feldspar and quartz. Your instructor tells you that the sediment was derived from one of two sites in
the area. Select the most likely site and explain your choice. What
name is given to this type of sandstone?
Site #1 A nearby exposure of weathered basaltic lava flows.
Site #2 An outcrop of granite at the previous field trip stop up the
road.
Every year about 20,000 pounds of stone, sand and gravel are
mined for each person in the United States.
a. Calculate how many pounds of stone, sand, and gravel will be
needed for an individual during an 80-year lifespan.
b. If one cubic yard of rock weighs roughly 1700 pounds, how big a
hole (cubic yards) must be dug to supply an individual with 80
years’ worth of stone, sand, and gravel?
c. A typical pickup truck can carry about a half cubic yard of rock.
How many pickup truck loads would be necessary during the
80-year span?
7
6
Key Terms
bedding planes (p. 166)
beds (strata) (p. 166)
biochemical origin (p. 156)
cap rock (p. 171)
cementation (p. 161)
chemical sedimentary
rocks (p. 151)
clastic (p. 162)
compaction (p. 161)
cross-bedding (p. 166)
crystalline texture (p. 163)
detrital sedimentary
rocks (p. 151)
diagenesis (p. 161)
environment of deposition
(p. 163)
evaporites (p. 159)
fossil fuel (p. 170)
fossils (p. 168)
graded beds (p. 166)
lithification (p. 161)
mud cracks (p. 168)
nonclastic (p. 163)
nonmetallic mineral
resources (p. 168)
oil trap (p. 171)
organic sedimentary rocks
(p. 151)
reservoir rock (p. 171)
ripple marks (p. 166)
salt flats (p. 160)
sedimentary environment
(p. 163)
sorting (p. 153)
strata (beds) (p. 166)
174
G I V E I T S O M E T H O U G H T
Dust collecting on furniture is an everyday example of a sedimentary
process. Provide another example of a sedimentary process that
might be observed in or around where you live.
Discuss two reasons sedimentary rocks are more likely to contain
fossils than igneous rocks.
Imagine you are studying sedimentary deposits in an abandoned
river channel. You see layers of well-sorted sand alternating with
coarser-grained, poorly sorted material consisting of sand, gravel,
and rock fragments. How would you interpret the history of this
river channel based on these layers of sediment? What might the
layers indicate about possible changes in climate conditions and the
flow of water in the river in the past?
If you hiked to a mountain peak and found limestone at the top,
what would that indicate about the likely geologic history of the
rock atop the mountain?
In which of the environments illustrated in Figure 6.18 would you
expect to find:
a. A deposit consisting of several beds in which sediment sizes in
each bed decrease from bottom to top.
b. An evaporite deposit.
c. A well-sorted sand deposit.
d. A deposit that includes a high percentage of partially decomposed plant material.
5
4
3
2
1
While on a field trip with your geology class, you stop at an outcrop
of sandstone. An examination with a hand lens shows that the sandstone is poorly sorted and rich in feldspar and quartz. Your instructor tells you that the sediment was derived from one of two sites in
the area. Select the most likely site and explain your choice. What
name is given to this type of sandstone?
Site #1 A nearby exposure of weathered basaltic lava flows.
Site #2 An outcrop of granite at the previous field trip stop up the
road.
Every year about 20,000 pounds of stone, sand and gravel are
mined for each person in the United States.
a. Calculate how many pounds of stone, sand, and gravel will be
needed for an individual during an 80-year lifespan.
b. If one cubic yard of rock weighs roughly 1700 pounds, how big a
hole (cubic yards) must be dug to supply an individual with 80
years’ worth of stone, sand, and gravel?
c. A typical pickup truck can carry about a half cubic yard of rock.
How many pickup truck loads would be necessary during the
80-year span?
7
6
Key Terms
bedding planes (p. 166)
beds (strata) (p. 166)
biochemical origin (p. 156)
cap rock (p. 171)
cementation (p. 161)
chemical sedimentary
rocks (p. 151)
clastic (p. 162)
compaction (p. 161)
cross-bedding (p. 166)
crystalline texture (p. 163)
detrital sedimentary
rocks (p. 151)
diagenesis (p. 161)
environment of deposition
(p. 163)
evaporites (p. 159)
fossil fuel (p. 170)
fossils (p. 168)
graded beds (p. 166)
lithification (p. 161)
mud cracks (p. 168)
nonclastic (p. 163)
nonmetallic mineral
resources (p. 168)
oil trap (p. 171)
organic sedimentary rocks
(p. 151)
reservoir rock (p. 171)
ripple marks (p. 166)
salt flats (p. 160)
sedimentary environment
(p. 163)
sorting (p. 153)
strata (beds) (p. 166)