Sedimentary Rocks

To get you thinking…

• Explain how these

different layers of

rock formed?

• Why are these layers

different colors?

Bryce Canyon, Utah

Badlands, South Dakota

Sedimentary Rocks

Weathering

Whenever rock is exposed at earth’s surface, it is

continuously being broken down by weathering.

Weathering – a set of physical and chemical

processes that breaks rock into smaller pieces

Sediments – small pieces of rock that are moved and

deposited by water, wind, glaciers and gravity

Sediments range in size from huge boulders to

microscopic particles

Sedimentary Rocks

Weathering

Physical weathering occurs when rocks are physically

broken down into smaller pieces

Sedimentary Rocks

Weathering

Chemical weathering occurs when minerals in rock are

dissolved or chemically changed

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Erosion

Erosion – the removal and transport of sediment

There are four main agents of erosion

Wind

Moving Water

Gravity

Glaciers

Sedimentary Rocks

Deposition

Deposition occurs when sediments are deposited on the

ground or sink to the bottom of a body of water

As particles of sediment are being carried by water

eventually settle out, layers of sediment will form at

the bottom according to size

Larger particles will settle to the bottom first,

followed by progressively finer particles on the top

Sedimentary Rocks

Deposition

Sediment deposited by wind usually consists of fine-

grained sand

Sediment deposited by glaciers usually consists of

materials that vary in size

Sedimentary Rocks

Lithification

Lithification – the physical and chemical processes

that transform sediments into sedimentary rocks

There are two processes that convert loose sediment to

sedimentary rock – compaction and cementation.

Compaction – the process in which the volume

and porosity of a sediment is decreased by the

weight of overlying sediments as a result of

burial beneath other sediments

Sedimentary Rocks

The high water

content and flat

shape of particles in

mud cause it to

compact greatly

when subjected to

the weight of

overlying sediments.

Sedimentary Rocks

Lithification

Cementation – the process in which minerals

precipitate into pore spaces between sediment

grains and bind sediments together to form rock

Sedimentary Rocks

Sedimentary Rock – rocks made up of a combination

of different types of sediment

Sedimentary Rocks

Clastic Sedimentary Rocks

Clastic sedimentary rocks – formed from deposits of

loose sediments that accumulate on Earth’s surface

Classified according to the sizes of their particles

Coarse-grained (>2 mm)

Medium-grained (1/16 mm to 2 mm)

Fine-grained (1/256 mm – 1/16 mm)

Sedimentary Rocks

Coarse-grained rocks

Conglomerate – rock that

is composed of rounded

fragments ranging in size

from fine mud to boulders

Sedimentary Rocks

Coarse-grained rocks

Breccia – a type of

conglomerate that is

composed of fragments

that are angular and have

sharp corners

Sedimentary Rocks

Medium-grained rocks

Sandstone – rock that is composed of sand sized

particles that have been cemented together

Porosity – the percentage of open spaces between

grains in a rock

Sandstone can have a porosity as high as 30%

Valuable layer as underground reservoirs of oil,

natural gas, and groundwater

Sedimentary Rocks

Sedimentary Rocks

Fine-grained rocks

Shale – rock that is composed of clay sized particles that

are cemented and compacted together

Has low porosity and forms barriers that hinder the

movement of groundwater and oil

Sedimentary Rocks

Shale

Sedimentary Rocks

Chemical sedimentary rocks

Chemical sedimentary rock – sedimentary rock that

forms when minerals precipitate from a solution or

settle from suspension

When water evaporates, the minerals that were

dissolved in the water are left behind.

The minerals left behind form rocks called

evaporates.

Sedimentary Rocks

Chemical sedimentary rocks

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Halite

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Gypsum

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Biochemical sedimentary rocks

Biochemical sedimentary rock – sedimentary rock

that forms from the remains of once-living plants or

animals

Limestone is the most abundant of these rocks

Composed primarily of calcite

Coal is also a biochemical rock that formed when

ancient fern-like plants that grew in swampy areas

Composed primarily of carbon

Sedimentary Rocks

Coal Fossiliferous

Limestone

End of Sedimentary Rocks