Sedimentary Rocks

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Sedimentary Rocks
Chemical Precipitates
Transport
Weathered Rock
Solution
Authigenic Minerals
Fresh Rock
Bedload
Secondary Minerals
Detrital minerals
Deposition
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Mineralogy
Detrital quartz orthoclase plagioclase
Secondary clay minerals
Authigenic
Precipitated calcite aragonite
3
Sandstones
4
Carbonates
5
Shales
6
Trace Elements
7
Chemical Weathering

• Reaction of mineral grains and water in the
  presence of an oxygen-rich atmosphere at low
  temperature and low pressure.
• Congruent dissolves completely no new minerals
  are formed.
• Incongruent dissolves and forms a different
  mineral (secondary mineral)

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Compositional Change
9
Compositional Changes
Fwt
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Types of Chemical Reactions

• Dissolution
• Hydrolysis
• Oxidation
• Hydration

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Simple Dissolution
Halite ? dissolved ions
Gypsum ? dissolved ions
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Congruent Hydrolysis
Calcite
13
Congruent Hydrolysis
Quartz
hydration
14
Congruent Solubility - SiO2
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Incongruent Hydrolysis
Feldspar
kaolinite
muscovite
16
K-Al-silicates
Muscovite
K-feldspar
Gibbsite
Pyro- phyllite
Kaolinite
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Oxidation
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Hydration
Anhydrite water ? gypsum
Hematite water ? goethite
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Chemical Reaction Rates

• Reactions proceed more rapidly at higher
  temperatures.
• The smaller the grain size the more rapidly the
  reaction proceeds to completion.
• Must replenish reactants and remove products for
  the reaction to proceed.

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Alteration
quartz clays muscovite
Stable
Remain as residue
Slow
Weathering Rate
K-feldspar biotite Na-plagioclase amphibole pyrox
ene Ca-plagioclase olivine calcite halite
Unstable
Soluble Components Dissolved ions removed in
solution
Insoluble components Stable minerals produced
by weathering
Fast
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Controls on Weathering

• Rock type
• Climate
• rainfall
• temperature
• relief
• time