BIOGEOSPHERE
Bilingual Biology and Geology
I.E.S. "J.S.Elcano (Sanlúcar Bda.)
3.3. Sedimentary rocks
a) Types of sedimentary rocks
Sedimentary rocks are classified into three groups: detrital,
chemical and organic.
- Detrital rocks are made up of fragments of other rocks
that are stuck together.
- Chemical sedimentary rocks are made of mineral crystals
from oceans, lakes and groundwater that have dissolved in water.
- Organic sedimentary rocks are made of plant and animal
remains which have been transformed into minerals.
b) Formation of sedimentary rocks
It begins with the accumulation and consolidation of sediment
or of rock fragments.
Rocks are fragmented by:
- Weathering.
Rocks at the surface of the Earth are broken up
by the action of atmospheric phenomena (changes in
temperature, rain, etc), or by the activities of plants and
animals.
- Erosion.
These broken fragments of rocks are swept away
by running water, glaciers, waves or wind.
The deposited sediments are transformed into compact, cohesive
rocks by two processes:
- Compaction. The weight of successive layers of sediment
compacts the sediments. This pressure reduces the spaces
between the fragments and squeezes out the water.
As a result, salt crystals are formed.
- Cementation. The rock fragments are stuck together
with the salt crystal which formed when the water was
eliminated.
Each layer of sediments is transformed into a layer of sedimentary
rock, called a stratum.
Organic sedimentary rocks are formed because the rests of vegetation
and microscopic marine animals and plants was covered
quickly by sediments, avoiding the putrefaction. In this environment,
of high pressure and temperature and without air, some kind of
bacteria changes the organic matter into coal or oil.
c) Fossils
Sedimentary rocks sometimes
contain remains of living things
that lived millions of years ago.
These remains are called fossils.
Fossils become part of the rocks,
during the processes of compaction
and cementation of sediments.
Fossils provide invaluable
information about the history
of life on Earth.
READING ACTIVITIES
After reading the text, copy and answer the following questions into your notebook:
Remember: you must make complete sentences.
3.7. Name some examples of:
a. Detrital sedimentary rocks
b. Chemical sedimentary rocks
c. Organic sedimentary rocks
3.8. Define:
a. Compaction
b. Fossil
c. Stratum
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Eva Mª
López Rodríguez
Departamento
Biología y Geología
IES " J. S. Elcano"
Sanlúcar de Barrameda