Sedimentary rock is created when existing rock breaks down into
sediments, and then the sediments are recombined by compaction and
cementation
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Sedimentary Rock Sediments are created by three forces:
Weathering Erosion Deposition
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Weathering Weathering is any process that breaks down rock.
There are two types of weathering Chemical weathering Mechanical
weathering
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Chemical Weathering Chemical Weathering is the transformation
of rock into one or more new compounds Water is the most important
agent of chemical weathering
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Mechanical Weathering Mechanical weathering occurs when
physical forces break rock into smaller and smaller pieces without
changing its composition
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Mechanical Weathering Three forces account for the majority of
mechanical weathering: Frost wedging Unloading Biological
Activity
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Frost Wedging When liquids freeze they expand, causing rock to
break apart.
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Unloading Unloading occurs when pressure is removed from a rock
body causing it to expand and break
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Biological Activity The activities of plants and animals can
cause rock to break apart For example tree roots can break through
rock layers, or borrowing animals creating holes in rock.
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Erosion Erosion is the removal of rock and its movement by
water, wind, ice, or gravity.
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Deposition When water, wind, ice or gravity loses energy the
sediments are released and deposited in a new area. Sediments are
deposited according to size, with larger sediments being released
first
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Sedimentary Rock Compaction and cementation are the two
processes that change sediment into sedimentary rock.
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Compaction Compaction is a process that squeezes, or compacts
sediments
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Cementation Cementation takes place when dissolved minerals are
deposited in tiny spaces among the sediments. These minerals hold
the sedimentary rocks together
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Classification of Sedimentary Rock Sedimentary rocks like
igneous rock can be classified into two groups based on how the
form: Clastic Sedimentary Rock Chemical Sedimentary Rock
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Clastic Sedimentary Rock Clastic Sedimentary Rocks are created
when weathered bits of rocks or minerals are cemented together
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Chemical and Biochemical Sedimentary Rocks Chemical Sedimentary
rocks are created when dissolved minerals precipitate from water
solutions Biochemical Sedimentary rocks are created when living or
once living materials are cemented together
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Features of Sedimentary Rock Sedimentary rock can have unique
features that can help us interpret the history of the Earth. Some
Features include: Ripples Mud Cracks Fossils