SEDIMENTARY ROCKS, METAMORPHIC ROCKS, AND AGE DETERMINATION

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SEDIMENTARY ROCKS, METAMORPHIC ROCKS, AND AGE
DETERMINATION
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SED-MET ROCKS-AGE

• Sedimentary rock family
• Definition and Explanation
• comprised of sediments
• accumulated from physical and or chemical
  processes mostly in large bodies of water
• consolidated through lithification

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SED-MET ROCKS-AGE

• Factors and concepts related to rock formation
• weathering--breaking down of rock materials at
  or near surface of Earth
• chemical--decomposition of materials and
  formation of new substances through removal of or
  additions to the weathered material
• physical or mechanical--disintegration of
  materials with no new substances forming

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SED-MET ROCKS-AGE

• Erosion
• removal or transportation of material by stream
  water, glacial ice, wind, and gravity
• eroded materials may eventually accumulate in
  large amounts
• Lithification
• compaction and cementation of sediments to become
  rocks

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SED-MET ROCKS-AGE

• Stratification
• accumulations in layers (strata or beds) and is
  the most common occurrence of this family of rock
• Law of superposition
• in a series of strata, each layer is older than
  the one above and younger than the one
  below--this reflects a relative age relationship
  between layers

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Stratification in Sedimentary Rocks
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SED-MET ROCKS-AGE

• Sedimentary rock types
• three types based on the way they form clastic
  (detrital), chemical inorganic, and organic
• clastic
• sediments accumulated primarily by physical
  processes as deposits from stream water, glacial
  ice, wind, etc. then lithified to rock

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SED-MET ROCKS-AGE

• Wentworths sediment size classification is used
  to name the specific clastic rock in the detrital
  class

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Wentworths Scale of Sedimentary Particles
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Different colors of beach sand in the world
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CLASTIC ROCKS
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Detrital (Clastic) Sedimentary Rocks
Larger grained
Conglomerate
Breccia
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Detrital (clastic) Sedimentary Sandstones
Graywacke
Arkose
Quartz Sandstone
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Detrital (clastic) Sedimentary Rocks
Smaller Grained
Claystone
Siltstone
Shale
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SED-MET ROCKS-AGE

• biological (organic) rocks
• accumulation of animal shells or plant material
  then lithified--particle size is not important in
  naming biological rocks

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SED-MET ROCKS-AGE
BIOLOGICAL OR ORGANIC ROCKS
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SED-MET ROCKS-AGE
White Cliffs of Dover
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COAL SERIES
Peat
buried plants
bituminous
lignite
anthracite
methane coal gas
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SED-MET ROCKS-AGE
Biological (organic) formed chert
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SED-MET ROCKS-AGE

• chemical (inorganic) rocks
• formed from chemical reactions in the oceans or
  large bodies of water

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CHEMICAL OR INORGANIC ROCKS
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Lakes formed from Glaciation
Lake Bonneville
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Evaporite deposits in Death Valley, California
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SED-MET ROCKS-AGE
Chemically (inorganic) formed chert---nodules of
chert caused by replacement of silica for
bedrockis present in the local Burlington
limestone bedrock in this area
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SED-MET ROCKS-AGE

• Some special features in sedimentary rocks
• cross bedding
• relatively thin layers inclined at an angle to
  the main bedding
• formed by currents in water or wind

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Cross bedding
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SED-MET ROCKS-AGE

• graded bedding
• a sedimentary layer characterized by a decrease
  in sediment size from bottom to top
• ripple marks
• small waves of sand that develop on surface of
  sedimentary layer by the action of moving water
  or wind

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Ripple marks
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SED-MET ROCKS-AGE

• Significance of sedimentary rocks
• only family of rock containing an abundant record
  of life forms and the changes in life forms
  throughout geologic time
• only family of rock in which natural gas,
  petroleum and coal are formed and found
• used as building materials, tombstones and some
  limestones are used as a source of lime

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Groundwater
Petroleum and Natural Gas
Coal
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Cement from Limestone
Salt
Uranium
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SED-MET ROCKS-AGE

• Metamorphic rock family
• Definition and explanation
• formed primarily through action of temperature
  and/or pressure on preexisting rocks
• little or no melting during process
• time is also an important factor
• rocks will loose evidence of fossils or other
  features present before the change

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SED-MET ROCKS- AGE

• Types of metamorphism
• contact or thermal
• usually forms with intrusions of smaller rock
  bodies as stocks in country rocks
• temperature associated with the intrusive body is
  the prime metamorphic agentlower temperatures
  would form lower grade of metamorphic rocks

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SED-MET ROCKS-AGE

• regional metamorphism
• usually forms with intrusions of larger bodies
  like batholiths or laccoliths
• temperature and pressure are equally important in
  the metamorphic process and includes a much
  larger area of metamorphismhigher temperatures
  would form a higher grade of metamorphic rock

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SED-MET ROCKS-AGE

• Kinds of metamorphic rocks
• all but one rock is comprised of silicate
  minerals
• foliated
• minerals are aligned in a pattern

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Foliated metamorphic rocks
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Foliated or Lineated Metamorphic Rocks
Slate
Gneiss
Schist
Gneiss
Phyllite
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Nonfoliated metamorphic rocks
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Non foliated Metamorphic Rocks
Quartzite (from arkose)
Marble
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SED-MET ROCKS-AGE

• Important uses
• building materials and tombstones
• marble can be used in art as a sculpturing
  material

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SED-MET ROCKS-AGE

• Age determination (geologic age)
• important concepts used
• relative age concepts
• crosscutting and intrusive nature of igneous
  rocks
• law of superposition pertaining to sedimentary
  rocks
• absolute age dating
• determination of amounts of radioactive parent
  and stable daughter

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Relative Age dating
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SED-MET ROCKS-AGE

• Age determination method
• relative and absolute age determination methods
  are used together to establish the absolute age
  of rocks which cannot themselves be dated
• igneous rocks are the best rock family to use in
  absolute age determinations
• Index fossils are used to facilitate the
  determination of the age of sedimentary rocks

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Determine the absolute age of sedimentary bed , B
given
1. igneous intrusive, V dated at 2.15 million
years old 2. lava flow, P dated at 2.25 million
years old (both V and P were dated using the
absolute age determin- ation method we
discussed in the mineral section)
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Correlation of Index Fossils From 2 Different
Areas