54
3.2.
Sedimentary rocks
Rocks found on the Earth’s surface are changed by the action of the wind, sea,
rivers, rain or ice. The elements wear down rocks in a process of
erosion.
The rock
fragments are deposited in the lowest areas of the Earth’s surface.
3.2.1.
Formation of sedimentary rocks
Sediments deposited in sedimentary basins (1) often follow two essential
processes for the formation of sedimentary rocks:
❚
Compaction
(2) is when sediments lose volume. Due to the weight
of the sediments on top, water is lost and the sediments become
compacted.
❚
Cementation
(3) takes place after the water is lost and the salts form
crystals. The crystals act like cement and stick the sediments together
to form sedimentary rocks.
❚
Sediments
are fragments of rock and organic material that have been
transported and deposited by water and wind.
❚
The places where sediments are deposited are called
sedimentary basins
.
The process in which sediments transform into sedimentary rocks is
called
diagenesis
or
lithification
.
Sedimentary basins: the origin of sedimentary rocks
Formation of sedimentary rock
Analyse
21.
2.5 cm of sediments are accumulated every 10 years in a
sedimentary basin. After the process of compaction, will
the volume of sediment be thicker or thinner? Explain your
answer.
22.
Explainwhywater is important in the formationof sedimentary
rocks.
