Transcript Sedimentary Rocks

Unit D Chapter 2
“Rocks and the Rock Cycle”
Lesson 2 Pgs D48-D53
SEDIMENTARY ROCKS
FORMATION OF SEDIMENTARY ROCKS
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Of all the rock on Earth’s
surface, 75% of it is
sedimentary rock.
But sedimentary rock is
only about 5% of the
crust.
Unlike igneous rock which
forms from material deep
in the Earth, sedimentary
rock forms from materials
on the surface.
FORMATION OF SEDIMENTARY ROCKS
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There are five steps to
forming a sedimentary
rock.
Weathering is the process
of breaking rock into
smaller pieces. Moving
water and freezing can
cause this.
Erosion is the movement
of sediment to new
locations by wind or water.
Water which was trapped in small cracks
kept freezing and expanding, slowly
cracking this boulder into smaller pieces.
FORMATION OF SEDIMENTARY ROCKS
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Deposition is the dropping
of sediment from wind,
water, or ice that slows
down.
Sedimentation is the
process of layers of
sediment building up for
millions of years.
The weight of the sediment
compacts or packs down
the sediment.
Cementation is the process
of gluing the particles
together.
Here you can see the layers of sediment
that were deposited over millions of
years.
THE TWO TYPES OF SEDIMENTARY ROCKS:
CLASTIC ROCKS
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Clastic Rocks are made
from sediments that were
weathered, transported
and deposited in layers.
Clastic Rocks are
classified by the size of
the particles that form
them.
Fine particles form shale,
medium particles form
sandstone.
Shale is the most common sedimentary
rock. 75% of sedimentary rock is shale or
siltstone.
CLASTIC ROCKS CONTINUED
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Rocks that have coarse,
pebble-sized particles with
rounded edges form
conglomerates.
The shape of the particles in
the rock can help you infer
how far from the source the
particles were deposited.
If the particles are rounded
and smooth, they traveled
farther and were worn
down.
Particles with sharp edges
did not travel as far.
This conglomerate’s particles are rounded
and smooth.
This type of conglomerate (Breccia) has sharpedged particles.
THE TWO TYPES OF SEDIMENTARY ROCKS:
CHEMICAL ROCKS
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Chemical Rocks are
formed from minerals that
were dissolved in water,
came out of a solution
and were then deposited.
Example: Mix salt and
water together to create a
solution. If you leave the
saltwater out, it will
eventually evaporate.
When it does, it leaves
behind salt crystals at the
bottom.
Stalactites and stalagmites are chemical
rocks. They are formed from billions of
drops of water leaving behind trace
amounts of minerals each time they fall.
THE TWO TYPES OF SEDIMENTARY ROCKS
CHEMICAL ROCKS
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Chemical sedimentary
rocks can also form from
animal shells and
skeletons.
Coral is actually a
chemical rock made of
limestone from the shells
of millions of coral.
Shells can also pile up on
the bottom of a lake or
ocean. With compaction
and cementation it can
form limestone.
Limestone is the most common
chemical sedimentary rock.
FOSSIL FORMATION
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Fossils are usually found in
sedimentary rock. They are
destroyed in igneous rocks.
They can sometimes be
found in metamorphic.
Fossils can form in different
ways, but it does not
happen easily.
In one method, the bones of
an animal are covered with
sediment and the calcium is
slowly replaced with
minerals from the ground.
This is “Sue”, one of the most complete
T-Rex skeletons discovered. 80% of the
original bones were found. Her remains
are on display in the Field Museum in
Chicago, Illinois.
FOSSIL FORMATION
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In another method, a
dead plant or animal may
fall into soft sediment and
become buried.
If the organic remains
decay completely, other
minerals can fill the
empty space creating a
mold or cast. This has let
us observe remains from
ancient species that did
not have bones.
USES OF SEDIMENTARY ROCKS
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Sedimentary Rocks are
used for a large variety of
resources.
Sandstone is a common
building material and used
to make glass.
Limestone and its forms
helps make concrete,
building materials, chalk
and antacids. (That’s why
some medicines taste
chalky…..they are chalk.)
Shale and coal are sources
of oil and natural gas for
energy.
This temple in Petra, Jordan was carved out
of a wall composed of sandstone. Anyone
recognize it from a certain movie with an
archaeologist with a bullwhip?
SO WHAT HAVE WE LEARNED?
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1. Sedimentary rock
makes up ___% of the
rock on Earth’s surface.
75%
2. There are two types of
sedimentary rock _______
and _______.
Clastic and chemical
3. What are the five steps
to forming a clastic rock?
Weathering, erosion,
deposition, sedimentation
and cementation.
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4. Why would you never
find a fossil in a chunk of
obsidian?
Obsidian is an igneous
rock, the fossil would be
destroyed from the lava.
5. Explain how a chemical
rock like stalactites form.
Dripping water leaves
behind deposits of
minerals eventually
building up to form a rock.