SEDIMENTARY ROCKS 7
INTRODUCTION
Sedimentary Rocks
CHAPTER OUTLINE
1.
2.
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3.
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4.
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5.
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6.
7.
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8.
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9.
10.
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LEARNING OBJECTIVES/FOCUS ON CONCEPTS
7.1 Discuss
7.2 Summarize
distinguish
7.3 Discuss describe
7.5 Outline
7.7 Summarize
7.9 List explain
TEACHING STRATEGIES
Clicker Questions:
Muddiest Point:
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A. Sedimentary Rock Identification
B. Sedimentary Environments and Facies
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TEACHER RESOURCES
Web Resources:
Sedimentary Rocks.
Places that display sedimentary rocks and structures:
o
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Coal Education
Imagery and Animations:
Images
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Animations
Sedimentary Rocks and Processes From UKY
ANSWERS TO QUESTIONS IN THE CHAPTER:
CONCEPT CHECKS
7.1 THE IMPORTANCE OF SEDIMENTARY ROCKS
1. The volume of sedimentary rocks in the crust is very small compared to the volume of igneous
2. Sedimentary rocks are important because they allow us to understand and reconstruct Earth
history through study of layers and formations that represent past conditions. Fossils aid in
7.2 ORIGINS OF SEDIMENTARY ROCKS
1. An exposure of granite may be mechanically weathered from frost-wedging and sheeting, and
chemically weathered through hydrolysis and dissolution. The products of this weathering
2. Detrital sedimentary rocks are formed from solid sediments (mud, sand, and gravel, for
example) derived from both chemical and mechanical weathering. Chemical sedimentary
7.3 DETRITAL SEDIMENTARY ROCKS
1. Clay minerals and quartz are the primary minerals found in detrital sedimentary rocks. Clays
2. Detrital sedimentary rocks are distinguished by particle size. Shales and udstones/siltstones
are composed of silt and clay sized grains, 1/2561/16 mm in size. Sandstones are composed
3. Sorting is the degree of similarity in particle sizes in a sedimentary rock. Transport of
sediment allows for sorting, and different transport agents sort sediments differently. Wind-
4. Conglomerate and breccia are both sedimentary rocks composed of particles of gravel-size,
7.4 CHEMICAL SEDIMENTARY ROCKS
1. Detrital rocks are the products of weathering; chemical sedimentary rocks are formed from
chemical sediments that form when ions in solution are precipitated by organic or inorganic
processes. Organic chemical sedimentary rocks are said to have a biochemical origin because
2. The primary difference in limestone, dolostone, and chert is composition. Limestone is a
general term given to any rocks that are composed primarily of calcium carbonate.
Biochemical forms of limestone include coquina (made from loosely cemented shells and shell
3. Evaporites form as water evaporates in a closed basin. As water evaporates from a main body
of water, the main body becomes concentrated in ions in solution. When this water becomes
7.5 COAL: AN ORGANIC SEDIMENTARY ROCK
1. The raw material for coal is organic matter. Dead plants will decompose quickly in the
2. Dead plant matter accumulates in an oxygen-poor environment, such as a swamp, where it is
attacked by bacteria and partially decomposed, liberating oxygen and hydrogen and
concentrating carbon. This partial decomposition forms peat, a soft brown material that
7.6 TURNING SEDIMENT INTO SEDIMENTARY ROCKS: DIAGENESIS AND LITHIFICATION
2. Compaction is most important as a lithification process in fine-grained sediments, such as
3. The three most common cementing agents in sedimentary rocks are calcite, silica, and iron
7.7 CLASSIFICATION OF SEDIMENTARY ROCKS
2. Clastic texture is associated with all detrital rocks and describes those rocks that consist of
broken fragments and particles that are cemented together. Non-clastic rocks are those rocks
7.8 SEDIMENTARY ROCKS REPRESENT PAST ENVIRONMENTS
2. Continental environments include stream, lake, glacial, and arid (eolian) environments.
3. A single rock layer may exhibit different types of sedimentary rocks as a representation of
7.9 SEDIMENTARY STRUCTURES
2. Cross bedding is layers of rock inclined to the horizontal, suggesting movement of sediment in
currents of wind or water. Graded bedding is layers of sediment that grade from coarse-
3. Mud cracks and ripple marks both suggest specific environmental conditions, and thus can be
used to reconstruct past environments. Mud cracks form in sediment that is alternatively wet
7.10 THE CARBON CYCLE AND SEDIMENTARY ROCKS
1. Carbon dioxide in the atmosphere combines with water to form carbonic acid; when this acidic
water comes in contact with carbonate rocks, soluble bicarbonate (HCO3–) is formed. This
2. Carbon may move from the geosphere to the atmosphere when chemical weathering of
EYE ON EARTH
EOE #1 GRANITE IN THE SIERRA NEVADA
1. This process occurs as granitic rock expands upon removal of overlying material. When
overlying material is eroded, the confining pressure on the granite drops and the rock
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EOE #2 CHEMICAL SEDIMENTARY ROCK IN YELLOWSTONE NATIONAL PARK
1. This rock likely has an inorganic origin, because its formation was not aided by life. The
3. This rock is likely travertine, also found as dripstone formations in caves (Figure 7.13).
EOE #3 NORTH CAROLINAS HATTERAS ISLAND
2. At point A, wave activity brings coarser sands to the shore, at point B, quieter waters
would deposit fine-grained sediments.
GIVE IT SOME THOUGHT
1. As a mass of igneous rock is uplifted and exposed at the surface, weathering processes begin to
act upon it. Chemical weathering of the silicate minerals in this rock will break down the
ferromagnesian minerals into clays and dissolved silica, which will be carried downstream. If the
rock contains quartz, the quartz grains will be released from the rock as the other minerals
chemically weather, and will be carried downstream as well. Other mechanical weathering
processes, such as frost wedging and sheeting, will also act to increase the surface area of rock
for further weathering.
If the material that made up this rock is deposited fairly close to its source, we might expect to
find arkose sandstone, composed of feldspathic grains and quartz in a cemented matrix. If the
2. In Chapter 3, clay is a term used to describe minerals that have a sheet structure. These
4. Limestone rock atop a mountain suggests that the area was once covered by a sea, where
5. All detrital rocks have a clastic texture. This means that they are composed of fragments of rock
6. A sedimentary rock rich in quartz may effervesce with acid if its cementing agent is calcite.
7. These layers are called graded beds. Graded beds form when sediment-laden water quickly loses
energy, often as currents of water enter a large quiet basin. When the water loses velocity, larger
8. The wave-like ridges on the surface are called ripple marks. Because these marks are
9.
a. An evaporate deposit would be found in an inland lake or sea, salt flat, or a playa lake
environment.
10. This sandstone likely originated from the outcrop of granite. It contains feldspars and quartz,
11. To determine if a rock with intergrown crystals is igneous or sedimentary, we would need to
determine the mineral composition of the crystals. The intergrown crystals of sedimentary rocks