Geology Ch. 6

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Sedimentary rock

Back 1

sediment that has been lithified into solid rock

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2 Sources of Sedimentary Rock

Back 2

(1)detrital material

(2)soluble material

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Detrital Material

Back 3

originates and is transported as solid particles from both mechanical and chemical weathering, which, when lithified, forms detrital sedimentary rocks

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Soluble Material

Back 4

produced largely by chemical weathering, which, when precipitated, forms chemical sedi¬mentary rocks.

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Diagenesis

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refers to:
physical
chemical
biological changes

that occur after sediments are deposited and during and after the time they are turned into sedimentary rock.

Burial promotes diagenesis. Diagenesis includes lithification.

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Lithification

Back 6

processes by which unconsolidated sediments are transformed into solid sedimentary rock.

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How are sedimentary rocks lithified?

Back 7

Compaction

Cementation

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Compaction

Back 8

Compaction: occurs when the weight of overlying materials compresses the deeper sediments.

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Cementation

Back 9

Cementation: the most important process by which sedi¬ments are converted to sedimentary rock, occurs when sol¬uble cementing materials, such as calcite, silica, and iron oxide, are precipitated onto sediment grains, fill open spaces, and join the particles.

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Particle size:

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the primary basis for distinguishing among various detrital sedimentary rocks.

The size of the particles in a detrital rock indicates the energy of the medium that transported them.

ex: gravels are moved by swiftly flowing rivers, whereas less energy is required to transport sand.

Common detrital sedimentary rocks include shale (silt- and clay-size particles), sandstone, and conglomerate (rounded gravel-size particles) or breccia (angular gravel-size particles).

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Percipitation of Chemical Sediments:

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inorganic processes

organic processes

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Inorganic Processes

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ex: evaporation and chemical activity

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Organic Processes

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ex: water-dwelling organisms that produce sediments of biochemical origin. Limestone, the most abundant chemical sedimentary rock, consists of the mineral calcite (CaCO3) and forms either by inorganic means or as the result of biochemical processes. Inorganic limestones include travertine, which is commonly seen in caves, and oolitic limestone, consisting of small spherical grains of calcium carbonate. Other common chemical sed-imentary rocks include dolostone (composed of the calcium-magnesium carbonate mineral dolomite), chert (made of microcrystalline quartz), evaporites (such as rock salt and rock gypsum), and coal (lignite and bituminous).

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2 groups of Sedimentary Rocks

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Detrital

Chemical

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Detrital

Back 15

All detrital rocks have a clastic texture, which consists of discrete fragments and particles that are cemented and compacted together. The main criterion for subdividing the detrital rocks is particle size.

ex:conglomerate
sandstone
shale


Chemical: The primary basis for distinguishing among different rocks in the chemical group is their mineral composition. Some chemical rocks, such as those deposited when seawater evaporates, have a nonclastic texture in which the minerals form a pattern of interlocking crystals. However, in reality, many of the sedimentary rocks classified into the chemical group also contain at least small quantities of detrital sedi¬ment. Common chemical rocks include limestone, rock gyp¬sum, and coal (e.g., lignite and bituminous).

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Chemical

Back 16

The primary basis for distinguishing among different rocks in the chemical group is their mineral composition. Some chemical rocks, such as those deposited when seawater evaporates, have a nonclastic texture in which the minerals form a pattern of interlocking crystals. However, in reality, many of the sedimentary rocks classified into the chemical group also contain at least small quantities of detrital sediment.

include:
limestone
rock gypsum
coal (e.g., lignite and bituminous).

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Sedimentary environments:

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places where sediment accumulates

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Sedimentary environments are
grouped into:


Each is characterized by certain:

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continental
marine
transitional (shoreline) environments


Physical
Chemical
biological con¬ditions

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Why is sediment important?

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Because sediment contains clues about the environment in which it was deposited, sedimentary rocks are important in the interpretation of Earth's history.

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Strata

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Layers, or beds, are probably the single most characteristic feature of sedimentary rocks.

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Other features charicteristic of sedimentary rocks:

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ripple marks
mud cracks
cross-bedding
graded bedding
fossils

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nonmetallic resources:

2 Groups

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Earth materials that are not used as fuels or processed for the metals they contain. Many are sediments or sedimentary rocks.


building materials
industrial minerals

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Fossil Fuels:

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Coal
Petroleum
natural gas

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Coal

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originates from large quantities of plant remains that accu¬mulate in an oxygen-deficient environment, such as a swamp. More than 70 percent of present-day coal usage is for the generation of electricity. Air pollution from the sulfur-oxide gases that form from burning most types of coal is a significant environmental problem.

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Petroleum

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formation is associated with the accumulation of sediment in ocean areas that are rich in plant and animal remains that become buried and isolated in an oxygen-deficient environment.

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Natural Gas

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natural gas: Oil and natural gas, which commonly occur together in the pore spaces of some sedimentary rocks, consist of various hydrocarbon compounds (compounds made of hydrogen and carbon) mixed together.
associated with sedimentary rocks

As the mo¬bile petroleum and natural gas form, they migrate and ac¬cumulate in adjacent permeable beds such as sandstone. If the upward migration is halted by an impermeable rock layer, referred to as a cap rock, a geologic environment de¬velops that allows for economically significant amounts of oil and gas to accumulate underground in what is termed an oil trap.