Volcanoes and Igneous Activity Earth Chapter 4

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Chapter 3 Sedimentary Rocks!
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Sedimentary Rocks

• The word sedimentary comes from the Latin word
  sedimentum, which means settling.
• Sedimentary rocks form when solids settle out of
  a fluid (water) or air and eventually become
  cemented together to form rocks.
• There are several different processes that create
  sedimentary rocks.

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Formation of Sedimentary Rocks
? Weathering

• Weathering is often the first step in the
  formation of sedimentary rocks.

• Sedimentary rocks form from both chemical and
  physical weathering.

• Chemical weathering takes place when the minerals
  in rocks change into new substances.

• Weathering also takes place when physical forces
  break the rock into smaller pieces.

• Living things can also cause both chemical and
  physical weathering.

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Weathering
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Formation of Sedimentary Rocks
? Erosion and Deposition

• Erosion involves the weathering and the
  removal of rock.
• There are four major agents of erosion
• Water, Wind, Ice, Gravity

• Deposition occurs when an agent of erosion loses
  energy and drops sediments.
• Sediments are deposited according to size.
• The smaller the sediment the further it
  travels.

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Agents of erosion
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Formation of Sedimentary Rocks

• After sediments are deposited, they often become
  lithified.
• Lithification is the process in which sediments
  compact or cement together to form rock.

? Compaction and Cementation
Compaction is a process that squeezes out the
water and compacts sediments through the force of
gravity (caused by the weight of the sediments)
Cementation takes place when dissolved
minerals are deposited in the tiny spaces among
the sediments.
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Conglomerate Sandstone

• Although these two rocks appear quite different,
  both formed when sediments were dropped by moving
  water.
• Conglomerate is made of rounded pebbles cemented
  together with visible cement.
• Sandstone is made of sand-sized grains cemented
  together with cement only visible using the aid
  of a microscope.

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Classification of Sedimentary Rocks
Sedimentary rocks can be classified into two
groups based on the way they are formed.
? Two Main Types
1. Clastic Sedimentary Rocks are composed of
weathered bits of pre-existing rocks and minerals.
Clastic sedimentary rocks are grouped
according to the size of the particles they
contain. The four particle sizes are (from
largest to smallest) 1.Gravel-sized contained in
breccias conglomerates 2.Sand-sized contained
in sandstones 3.Silt-sized contained in
siltstones 4.Clay-sized contained in the shale
which is the most common clastic sedimentary rock
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Clastic Sedimentary Rocks
Shale Breccia

• Shale and breccia are common clastic sedimentary
  rocks.
• Shale contains the smallest clast or particle
  size which are clay-sized particles.
• Breccia contains the largest particle clast or
  particle size which are gravel-sized particles
  and unlike conglomerate which has rounded
  particles their particles are very jagged.

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Classification of Sedimentary Rocks
? Two Main Types

• 2. Chemical sedimentary rocks form when dissolved
  substances precipitate, or separate, from water
  by either organic or inorganic means.
• This occurs when water either evaporates or boils
  off leaving a solid behind.

Common chemical sedimentary rocks include

• Limestone - the most abundant chemical rock

• Microcrystalline quartz rocks such as chert,
  flint, jasper, or agate

• Evaporites such as rock salt (halite) or rock
  gypsum

• Coal

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Biochemical Sedimentary Rocks

• About 90 of limestones are formed from
  biochemical sediments.
• An example of biochemical sediments are shells
  and skeletal remains of organisms that settle to
  the bottom of the ocean floor.

• Eventually these remains dissolve and form
  calcite cement which holds the shells together.
  This type of biochemical rock is called coquina.
• Chalk is a also biochemical rock formed from
  limestone.

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Classification of Sedimentary Rocks
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Hoodo

• Hoodoos are tall, isolated rock formations that
  are common in dry regions of sedimentary rock. In
  a place like central New Mexico, where this
  mushroom-shaped hoodoo stands, erosion commonly
  leaves bits of resistant rock protecting the
  weaker rock layer beneath it.
• The big geologic dictionary says that only a tall
  formation should be called a hoodoo any other
  shapea camel, sayis called a hoodo-rock. The
  defining feature of either one of these is that
  its shape is bizarre or fantastic. And a proper
  hoodoo (the word is the same as voodoo), it
  seems, must look like an image of the spirits
  that populate the voodoo cosmologythat is, it
  needs to be spooky. That's a curious eruption of
  folklore in a scientific glossary, and just
  another reason to love geology.

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Columns of rock called hoodoos at Bryce Canyon
National Park.
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Weathering1. Frost wedging2. Rain
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Sedimentary Rock Features

• Features of sedimentary rocks are clues to how
  and where the rocks are formed
• Each layer of sedimentary rock records a period
  of deposition.
• In undisturbed rocks, the oldest layers are found
  at
• the bottom and the youngest layers are found at
  the top of the rocks.

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Sedimentary Rock Features
Ripple marks indicate that the rock formed along
a beach or stream bed.
Mud cracks formed when wet mud or clay dried and
shrank, leaving cracks that filled in with other
sediments and solidified into rock.
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Sedimentary Rock Features

• Fossils!
• Fossils are the traces or remains of ancient life
• Fossils can be used to help answer many questions
  about the rocks they contain.
• The age of the rock.
• The environment in which the rock formed (land,
  lake, river, or ocean)
• The climate in which the rock formed (hot or
  cold, rainy or dry)
• Fossils also play a key role in matching up rocks
  from different places that are the same age.

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Get out a piece of paper

• What two properties are used to classify IGNEOUS
  rocks?
• How are sedimentary rocks formed?
• How are metamorphic rocks formed?
• What are the three types of sedimentary rocks?

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• 5. What shape are the pieces in breccia?
• 6. What is the Latin meaning for sedimentary?
• 7. What did chalk form from?

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Answers

• What two properties are used to classify IGNEOUS
  rocks?
• Texture and Composition
• How are sedimentary rocks formed?
• Compaction and cementation
• How are metamorphic rocks formed?
• Heat and pressure
• What are the three types of sedimentary rocks?
• Clastic, chemical, organic

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• 5. What shape are the pieces in breccia?
• angular
• 6. What is the Latin meaning for sedimentary?
• settle
• What did chalk form from?
• limestone