Download WORKSHEET 5 SEDIMENTARY ROCKS Activity 1

UNIT: EARTH`S EXTERNAL GEOMORPHOLOGY
SESSION 5 - WORKSHEET 5
SEDIMENTARY ROCKS
Activity 1 - Read this text about sedimentary rocks.
SEDIMENTARY ROCKS

Sediments
are
loose
materials
which
come
from
erosion
processes.
Sedimentary rocks are formed by sediment that is deposited over time in
layers on different areas of the Earth.

These sediments may include materials of different sizes which have been
carried by water or wind-accumulated in places such as valleys, lakes,
deltas
of
rivers,
coasts,
oceans,
etc.
These
are
called
depositional
environments.

Sediments settle in layers called strata, which can often be seen in exposed
cliffs. These layers are usually parallel. The oldest ones are at the bottom and
the most recent are at the top.

The weight of the sediments on top squashes the sediments at the bottom. This
is called compaction. The water and air are squeezed out from between the
pieces of rock so crystals of different salts form.

The crystals form a sort of glue that sticks the pieces of rock together. This
process is called cementation. It decreases the porosity of the sediment.

These processes eventually form a type of rock called sedimentary. It may take
millions of years for sedimentary rocks to form.

This is the order of the process:
sedimentation → compaction → cementation.

Sometimes these layers may have been folded or broken by the Earth's internal
forces originating faults and folds, as we can see in some cliffs.

Sedimentary rocks cover most of the Earth's rocky surface but only make up a
small percentage of the Earth’s crust compared to metamorphic and igneous
rocks.

Sedimentary rocks may contain fossils of animal and plants which were trapped
in the sediments as the rock was being formed.
FORMATION OF SEDIMENTARY ROCKS

These are the different processes in order:
sedimentation → compaction → cementation.

We classify sedimentary rocks according to their formation processes: detritic
rocks, organic rocks or precipitated rocks.

Detritic rocks are made of fragments of rocks of different sizes.
o Conglomerates: made from large grains of sediments (gravel or stones).

o
Sandstone: made from small grains.
o
Mudstone: made from clay.
Organic rocks include sediments with a high content of remains of living things
which are sometimes fossilized. Coal and oil (the only liquid rock) and shelly
limestone are organic rocks.

Precipitated rocks, like limestone, are formed as a result of the precipitation
of minerals dissolved in water.
Activity 2 - Production of visuals based on the text.

Mind maps, flow charts, cause-effect diagrams, etc.
Activity 3 - Loop activity.

Work with your partners to do the Loop Activity about Sedimentary Rocks in the
same way as for the Session 4.
Activity 4 - Fill the gaps in this text using the
words provided in the box.
SAND
EROSION
WIND
SEABED
LAYERS
REMAINS
FOSSILS
DETRITIC
PRECIPITATION ORGANIC
SQUEEZED
Some pieces of rock, such as gravel, _______ and clay, are called sediments.
They come from the _______ of other rocks. They are carried away by the
action of _______ and rivers. Most of them settle on the _______ near the
coast forming _______ . When the sediments are _______ together, they
turn into a sedimentary rock. Sometimes the layers of sediments contain
_______ of dead organisms, called _______. The sedimentary rocks made of
fragments are called _______ rocks. If they come from soluble materials they
are formed by _______ and if they come from living things, they are called
_______ rocks.
Activity 5
Read the situation below and put the strata in the correct order.
Imagine that you are lying on a beach near a cliff where you can see
different layers of sediments ordered like this:
a. A top layer of sandstone.
b. Shelly limestone.
c. Coal and plant fragments.
d. Conglomerate.
e. Mudstone in the bottom layer.
A. Draw a picture outlining the characteristic of the layers of the cliff.
B. Link each layer with the geological environments where it could have
been laid down: mouth of a river, sea bed, forest, coastal area.
a)
b)
c)
d)
e)