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| Lower Antelope
Canyon was carved out of the surrounding
sandstone by both mechanical weathering and
chemical weathering. Wind, sand, and water from
flash flooding are the primary weathering
agents. |
Sedimentary
Sedimentary rocks are types of rock that are formed by
the accumulation or deposition of mineral or organic
particles at the Earth's surface, followed by
cementation. Sedimentation is the collective name for
processes that cause these particles to settle in place.
The particles that form a sedimentary rock are called
sediment, and may be composed of geological detritus
(minerals) or biological detritus (organic matter). The
geological detritus originated from weathering and
erosion of existing rocks, or from the solidification of
molten lava blobs erupted by volcanoes. The geological
detritus is transported to the place of deposition by
water, wind, ice or mass movement, which are called
agents of denudation. Biological detritus was formed by
bodies and parts (mainly shells) of dead aquatic
organisms, as well as their fecal mass, suspended in
water and slowly piling up on the floor of water bodies
(marine snow). Sedimentation may also occur as dissolved
minerals precipitate from water solution.
The sedimentary rock cover of the continents of the
Earth's crust is extensive (73% of the Earth's current
land surface), but sedimentary rock is estimated to be
only 8% of the volume of the crust. Sedimentary rocks
are only a thin veneer over a crust consisting mainly of
igneous and metamorphic rocks. Sedimentary rocks are
deposited in layers as strata, forming a structure
called bedding. Sedimentary rocks are often deposited in
large structures called sedimentary basins. Sedimentary
rocks have also been found on Mars.
The study of sedimentary rocks and rock strata provides
information about the subsurface that is useful for
civil engineering, for example in the construction of
roads, houses, tunnels, canals or other structures.
Sedimentary rocks are also important sources of natural
resources including coal, fossil fuels, drinking water
and ores.
The study of the sequence of sedimentary rock strata is
the main source for an understanding of the Earth's
history, including palaeogeography, paleoclimatology and
the history of life. The scientific discipline that
studies the properties and origin of sedimentary rocks
is called sedimentology. Sedimentology is part of both
geology and physical geography and overlaps partly with
other disciplines in the Earth sciences, such as
pedology, geomorphology, geochemistry and structural
geology. |
|
Consolidation
Sedimentary rocks are types of rock that are formed by
the accumulation or deposition of mineral or organic
particles at the Earth's surface, followed by
cementation. Sedimentation is the collective name for
processes that cause these particles to settle in place.
The particles that form a sedimentary rock are called
sediment, and may be composed of geological detritus
(minerals) or biological detritus (organic matter). The
geological detritus originated from weathering and
erosion of existing rocks, or from the solidification of
molten lava blobs erupted by volcanoes. The geological
detritus is transported to the place of deposition by
water, wind, ice or mass movement, which are called
agents of denudation. Biological detritus was formed by
bodies and parts (mainly shells) of dead aquatic
organisms, as well as their fecal mass, suspended in
water and slowly piling up on the floor of water bodies
(marine snow). Sedimentation may also occur as dissolved
minerals precipitate from water solution.
The sedimentary rock cover of the continents of the
Earth's crust is extensive (73% of the Earth's current
land surface), but sedimentary rock is estimated to be
only 8% of the volume of the crust. Sedimentary rocks
are only a thin veneer over a crust consisting mainly of
igneous and metamorphic rocks. Sedimentary rocks are
deposited in layers as strata, forming a structure
called bedding. Sedimentary rocks are often deposited in
large structures called sedimentary basins. Sedimentary
rocks have also been found on Mars.
The study of sedimentary rocks and rock strata provides
information about the subsurface that is useful for
civil engineering, for example in the construction of
roads, houses, tunnels, canals or other structures.
Sedimentary rocks are also important sources of natural
resources including coal, fossil fuels, drinking water
and ores.
The study of the sequence of sedimentary rock strata is
the main source for an understanding of the Earth's
history, including palaeogeography, paleoclimatology and
the history of life. The scientific discipline that
studies the properties and origin of sedimentary rocks
is called sedimentology. Sedimentology is part of both
geology and physical geography and overlaps partly with
other disciplines in the Earth sciences, such as
pedology, geomorphology, geochemistry and structural
geology. |
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Types of sedimentary rock
Sediments are formed by three processes: |
- Solids swept down from the land.
- Bits & pieces laid down in water,
e.g. shells.
- Chemicals in solution, which may be
precipitated.
|
These sedimentary processes – weathering, transportation,
and deposition – reach three final end products: quartz
sand, shale (from clay), and limestone (CaCO3). Most
sedimentary rocks are variations on this general pattern.
Chalk, limestone, and dolomite are all basically made from
calcium carbonate. This comes from a mixture of minerals and
pieces of animals (especially animal shells). They are
mostly formed in oceans. Shales, sandstones, and
conglomerates are all clastic rocks. They are made from
pieces of other rocks. The pieces may have come from erosion
by water, ice or wind. Coal is made from ancient plants; oil
and natural gas is also organic in origin.
Some sedimentary rocks are made of just one type of
sediment, all about the same size, such as sand. Other
sedimentary rocks will have large and small lumps, and
pieces of different types of rock. Well-known sedimentary
rocks are sandstone and limestone. |
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Sedimentary rocks may be found anywhere on Earth. When
sedimentary rocks are heated and squeezed, they become
metamorphic rocks. Igneous rocks have a volcanic origin.
Over a very long time, rocks get recycled, in two ways.
When marine sediments are raised above sea level, they
get weathered, and the pieces carried down to the sea.
On a much longer time-scale continental plates may
collide. Then one plate goes under the other (is
subducted), and all its material is recycled, emerging
much later. |
|
 Kiddle: Sedimentary
Wikipedia: Sedimentary |
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