Sedimentary Rock
Sedimentary Rock
 Sedimentary rock is created when existing rock breaks down
into sediments, and then the sediments are recombined by
compaction and cementation
Sedimentary Rock
 Sediments are created by three forces:
 Weathering
 Erosion
 Deposition
Weathering
 Weathering is any process that breaks down rock.
 There are two types of weathering
 Chemical weathering
 Mechanical weathering
Chemical Weathering
 Chemical Weathering is the transformation of rock into
one or more new compounds
 Water is the most important agent of chemical weathering
Mechanical Weathering
 Mechanical weathering occurs when physical forces break
rock into smaller and smaller pieces without changing its
composition
Mechanical Weathering
 Three forces account for the majority of mechanical
weathering:
 Frost wedging
 Unloading
 Biological Activity
Frost Wedging
 When liquids freeze they expand, causing rock to break
apart.
Unloading
 Unloading occurs when pressure is removed from a rock
body causing it to expand and break
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.
Erosion
 Erosion is the removal of rock and its movement by water,
wind, ice, or gravity.
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
Sedimentary Rock
 Compaction and cementation are the two processes that
change sediment into sedimentary rock.
Compaction
 Compaction is a process that squeezes, or compacts
sediments
Cementation
 Cementation takes place when dissolved minerals are
deposited in tiny spaces among the sediments.
 These minerals hold the sedimentary rocks together
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
Clastic Sedimentary Rock
 Clastic Sedimentary Rocks are created when weathered
bits of rocks or minerals are cemented together
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
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