Download Two types of Sedimentary Rocks:

Remember Rocks &
Rock Cycle?
•Igneous (Previously)
•Sedimentary (Now)
•Metamorphic (Next)
Sedimentary rocks cover 65% of continental surface!
1/2 of these are <130 Ma
Two types of Sedimentary Rocks:
Clastic sedimentary rocks
(made from other rocks)
Chemical Sediments (minerals
precipitate from water)
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Clastic Sedimentary Rocks
Processes involved : Weathering, transportation, deposition, burial &
cementation
Weathering = physical disintegration and
chemical decomposition of rocks
• Mechanical weathering = physical and
biological forces break rocks into smaller
pieces
• Chemical weathering = inorganic and
organic chemical reactions alter the
mineralogy and composition of rocks
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Examples of Mechanical Weathering
• Frost Wedging
– This makes potholes in
the roads!
• Clay expansion is a
similar processes
where clay minerals
become wet and
expand, forcing open
cracks
• You should understand
these two processes
Frost wedging causes these boulders to break away from the cliff above.
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Joints/breaks in rocks
are pathways for fluids
Biologic activity also
serves to break rocks
Sheeting
Spheroidal
Weathering
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Physical weathering increases surface area!
This enhances chemical weathering, by increasing the
rates of chemical reactions!
Chemical Weathering: Chemical reactions between the rock and
water/atmosphere (e.g., Oxidation, hydration, solution)
Dissolved Ions are
transported away
with the fluid
Surface becomes
pitted as mass is
lost. Stable minerals
left as sediment/soil
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Sediment is Transported & Deposited
Water transport: oceans
and rivers
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Sediment is Transported & Deposited
Transport by Ice
Transport by Wind
Deposition of Sediment
• Look around you: Sediment is always in transport and environments of
deposition are as varied as Earth’s landscape.
• Ultimate destination of sediment is the bottom of the ocean - gravity
ultimately forces sediment to ‘lowest spot’
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Cementation
Sediment Maturity
• Rounding
• Sorting
• Porosity & Permeability
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Sedimentary Structures indicate environments of deposition!
For Example: Complex outcrop
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New type of sedimentary rock: Chemical Sediments
Two types: Biogenic Precipitates and Chemical Precipitates
Biogenic Precipitates
• Organism excretes hard
parts (shells)
– These accumulate as
fossils = sediment
• Limestones = rock
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Chemical Precipitates
• Minerals crystallize from water laden with dissolved ions
– From where?
• Why do mineral precipitate?
– Change in T, pH or chemical environment (potential)
Rocksalt or Evaporites
Chert!
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