Download - Chapter 7 Sedimentary Rocks
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Chapter 7 Sedimentary Rocks
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What is a sedimentary rock? Sedimentary rocks are products of
mechanical and chemical weathering They account for about 5% (by volume) of
Earth’s outer 10 miles Contain evidence of past environments
• Provide information about sediment transport
• Often contain fossils
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What is a sedimentary rock? Sedimentary rocks are important for
economic considerations because they may contain
• Coal• Petroleum and natural gas• Sources of iron, aluminum, and manganese
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Turning sediment into rock Many changes occur to sediment after it is
deposited Diagenesis = chemical, physical, and
biological changes that take place after sediments are deposited
• Occurs within the upper few kilometers of Earth’s crust
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Turning sediment into rock Diagenesis
• Includes• Recrystallization – development of more stable
minerals from less stable ones• Lithification – sediments are transformed into
solid rock by • Compaction and cementation• Natural cements include calcite, silica, and
iron oxide
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Types of sedimentary rocks
Sediment originates from mechanical and/or chemical weathering
Rock types are based on the source of the material
• Detrital rocks – transported sediment as solid particles
• Chemical rocks – sediment that was once in solution
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Detrital sedimentary rocks
The chief constituents of detrital rocks include
• Clay minerals• Quartz-clear or any color • Feldspars - pink• Micas – biotite, muscovite
Particle size is used to distinguish among the various rock types
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Detrital sedimentary rocks
Common detrital sedimentary rocks• Shale
• Mud-sized particles in thin layers that are commonly referred to as laminea
• Most common sedimentary rock• Sandstone
• Composed of sand-sized particles• Forms in a variety of environments• Quartz is the predominant mineral
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Laminae = layers about 1 cm thick or less
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Shale with plant remains
Figure 7.2
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Quartz sandstone
Figure 7.4
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Detrital sedimentary rocks
• Conglomerate and breccia• Both are composed of particles greater than
2mm in diameter• Conglomerate consists largely of rounded
gravels
• Breccia is composed mainly of large angular particles
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Conglomerate
Figure 7.6
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Breccia
Figure 7.7
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Chemical sedimentary rocks
Consist of precipitated material that was once in solution
Precipitation of material occurs by• Inorganic processes• Organic processes (biochemical origin)
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Chemical sedimentary rocks
Common chemical sedimentary rocks• Limestone
• Most abundant chemical rock• Composed chiefly of the mineral calcite• Marine biochemical limestones form as coral
reefs, coquina (broken shells), and chalk (microscopic organisms)
• Inorganic limestones include travertine and oolitic limestone
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Coquina
Figure 7.9
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Fossiliferous limestone
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Chemical sedimentary rocks Common chemical sedimentary rocks
• Dolostone• Typically formed secondarily from limestone
• Chert• Composed of microcrystalline quartz • Varieties include flint and jasper (banded form
is called agate)
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Agate
Figure 7.12 A
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Chemical sedimentary rocks Common chemical sedimentary rocks
• Evaporites• Evaporation triggers deposition of chemical
precipitates• Examples include rock salt and rock gypsum
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Chemical sedimentary rocks Common chemical sedimentary rocks
• Coal• Different from other rocks because it is
composed of organic material • Stages in coal formation (in order)
• 1. Plant material• 2. Peat• 3. Lignite• 4. Bituminous
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Stagesof
coal formation
Figure 7.15
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Stagesof
coal formation
Figure 7.15
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Classification of sedimentary rocks
Sedimentary rocks are classified according to the type of material
Two major groups• Detrital• Chemical
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Classification ofsedimentary rocks
Two major textures are used in the classification of sedimentary rocks
• Clastic• Discrete fragments and particles• All detrital rocks have a clastic texture
• Nonclastic• Pattern of interlocking crystals• May resemble an igneous rock
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Identification of sedimentary rocks
Figure 7.17
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Sedimentary environments
A geographic setting where sediment is accumulating
Determines the nature of the sediments that accumulate (grain size, grain shape, etc.)
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Sedimentary environments
Types of sedimentary environments• Continental
• Dominated by stream erosion and deposition • Glacial• Wind (eolian)
• Marine• Shallow (to about 200 meters)• Deep (seaward of continental shelves)
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Sedimentary environments
• Transitional (shoreline)• Tidal flats• Lagoons• Deltas
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Sedimentaryenvironments
Figure 7.19 (left)
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Sedimentaryenvironments
Figure 7.19 (right)
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Sedimentary environments
Sedimentary facies• Different sediments often accumulate
adjacent to one another at the same time• Each unit (called a facies) possesses a
distinctive set of characteristics reflecting the conditions of a particular environment
• The merging of adjacent facies is a gradual transition
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Sedimentary facies
Figure 7.20
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Sedimentary structures
Provide information useful in the interpretation of Earth history
Types of sedimentary structures• Strata, or beds (most characteristic of
sedimentary rocks)• Bedding planes that separate strata• Cross-bedding
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Sedimentary structures
Types of sedimentary structures• Graded beds• Ripple marks• Mud cracks• Fossils
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End of Chapter 7