Download Sedimentary rocks

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Chapter 4-4
Sedimentary Rocks Study Guide
Ms. Grady
Formation of Sedimentary Rocks
 Igneous rocks are the most common rocks on Earth. Most igneous rocks
are below the surface which means you might not have seen too many of
them.
 75% or the rocks exposed at the surface are sedimentary rocks.
Sediments = lose materials.
Examples, rock fragments, mineral grains, and bits of shell (that have been
moved by wind, water, ice, or gravity).
Where do sediments come from? → Look at the rock cycle and you can see
they come from already-existing rocks that are weathered and eroded.
Weathering = surface processes that work to break down rock mechanically
or chemically (breaks rock down into smaller pieces).
Sedimentary rocks = forms when sediments are pressed and cemented
together, or when minerals form from solutions.
Classifying Sedimentary Rocks
The most widely used classification system for sedimentary rock places them into three
main categories according to the origin of the materials from which they are made
Clastic or Detrital Rocks Organic Rocks
Chemical Rocks
(from sediments)
(from living creatures)
(from a solution of water)
*detrital comes from the
Latin word “detritus” =
wears away
___________________ ___________________ _________________________
Examples
Examples
Examples
Conglomerate
Shale
Sandstone
Breccia
Coquina
Coal
Chalk
Fossil –rich Limestone
Gypsum
Limestone – the most abundant
sedimentary rock.
They are classified according to their size and shape of the fragments in them.
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Clastic or Detrital Rocks
Conglomerate
Sandstones
Shale
Breccia
If over a third of the
rock is made of pebbles
the rock is called
conglomerate.
Clastic rocks made of
small sand-sized grains
are called sandstones.
Many geologists use the
term shale to describe
all the clastic rock that
are made from particles
smaller than sand.
The pebbles in
At least half the particles Shale forms from small
conglomerates are
in a clastic rock must be
particles of mud and
smooth and rounded
sand- sized in order for it clay that settle at the
because they have been to be considered a
bottom of quiet bodies
worn down by the action sandstone.
of water. For example,
of water. They are also
swamps.
called puddling stones.
Breccia is sharp and
Sandstones are very
Most shale can be split
usually has pointed
common rocks. They are
into flat pieces.
corners.
formed from the sand on
beaches in riverbeds and
in sand dunes.
In a sandstone rock, the
grains are cemented
together by minerals.
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Erosion – moving sediments by running water such as: streams, rivers, waves,
glaciers, and wind.
Deposit = when sediments settle in one place.
Compaction = Layer upon layer of sediments build up. Pressure from the upper
layers pushes down on the lower layers (levels)
Sedimentary rock formation
The river transports bits of rock, and deposits them on the bottom of the river bed.
Sedimentary rock formation
Deposited rocks build up in layers, and the weight of the top layers compresses the bottom
layers
Sedimentary rock formation
The compression squeezes out water, leaving salt crystals that cement the rocks together.
Notice in compaction that the pore space decreases (-) which causes them to become
packed together more tightly.
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Cementation
 If sediments are large (for example sand and pebbles), pressure can’t
make them stick together.
 Therefore, large sediments have to be cemented together.
 When water moves through soil (dirt) and rock, it picks up materials
released (let go) from minerals during weathering.
 Cementation happens when minerals (for ex. quartz, calcite, and hematite)
are deposited between the pieces of sediments.
 When this happens the minerals then act like cement or glue and hold the
sediments together making a detrital sedimentary rock.
Organic Sedimentary Rocks
 Organic Rocks come from organisms (living things, ex. creatures, animals,
plants).
 Limestone are often but not
always organic rocks.
 Deposits of limestone may
form from the shells of
Ex. of calcite limestone
creatures when they die.
 Creatures may also cement
their shells together and over
time form reefs.
 Coal is also made from the
Ex. of coal
remains of living things. It is
made from plants that lived
millions of years ago.
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Chemical Rocks
 Chemical rocks were dissolved in water.
 When a sea or lake dries up, it can leave
large amounts of minerals that are
dissolved in water.
For example,
rock salt and gypsum
 Some limestone rocks are formed by in
organic processes in caves called
travertine.
Ex. of Rock Salt
Ex. of Gypsum
Picture of a cave.
As water evaporates (disappears), a thin
deposit of limestone is left behind.
 Calcium carbonate is carried in solution in ocean water.
 When the calcium carbonate comes out of a solution as calcite, the crystals
grow together and limestone forms.
 Limestone is 50% calcite.
Rock Salt
 When water that is rich in salt evaporates (disappears), it deposits the
mineral halite.
 Halite forms from rock salt.
 Rock salt deposits can be as thick as 400 meters.
 Companies mine these salts.
It is used in making glass, paper, soap and dairy products.
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Mine in Germany where rock salt is dug up and
pull out of the mine.
 The halite is processed for table salt.
Environmental Clues
 If a sedimentary rock has preserved mud cracks, then it formed in an area
that alternated between WET and DRY.
 Rocks with ripple marks, formed in an area that alternated between
moving WATER and AIR.
 If a sedimentary rock is made of large particles, then it formed near
where it originated.
 If the particles are small, it formed far from the place where the
particles originated.
 Evaporates, (ex. rock salt) form in areas that were very dry and arid.
Use of Rocks
Mount Rushmore is made from granite.
The Taj Mahal and the Parthenon were made of marble.
Notre Dame Cathedral in Paris and many of the Egyptian pyramids were made of
limestone.
***Don’t forget we extract salt from mines. Salt is used to make glass, paper,
and soap.
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Rocks in Nature
Basaltic Rock is formed
mainly under the ocean,
Granite rock is found in
continental mountains.
Ex. In areas like the mid- Ex. Yosemite National
Atlantic Ridge and in
Park.
Volcanic mountains like
Hawaii
Andesitic rocks are
found in continental
volcanoes.
Ex. Mt. Rainer