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Sediments and Sedimentary
Rocks
Significance for Climate and CCS
 Form at the surface, so directly influnced by Earth’s
climate, provide the climate record
 Provide reservoir and seal lithologies
The Rock Cycle
Major Sediment/ Sedimentary
Rock Types

Clastics
•

Particles of preexisting rock
Chemical and biochemical
•
Precipitated from solution
Clastics
• Particles of preexisting rock
• Effect of weathering
• Dominantly silicate minerals
Gravel and conglomerate/breccia
• > 30% of grains > 2mm
• Conglomerate if rounded, breccia if angular
• Need strong currents
Sand and sandstone
• Dominantly sand sized particles (.062 - 2 mm)
Sand and sandstone
• Dominantly sand sized particles (.062 - 2 mm)
• Major kinds of sandstones
• Quartz arenites
Quartz arenite
Sand and sandstone
• Dominantly sand sized particles (.062 - 2 mm)
• Major kinds of sandstones
• Quartz arenites
• Arkoses
Arkose
Sand and sandstone
• Dominantly sand sized particles (.062 - 2 mm)
• Major kinds of sandstones
• Quartz arenites
• Arkoses
• Lithic arenites
•
Graywacke (wacke)
Graywacke
Mud and mudrock
• Particles dominantly (<0.062)
• Silt and siltstone (0.062 - 0.004 mm)
• Clay and claystone (<0.004 mm)
• Weak to no currents
Shale
(Mudrock)
Chemical and biochemical
• Precipitated from solution
• Formed at or near place of deposition
• Dominantly carbonates & evaporites
• Classified by chemical composition
Carbonates
• Limestone (CaCO3)
• Dolostone (CaMg(CO3)2)
The White Cliffs of Dover
Evaporites
 Halite (NaCl)
 Gypsum (CaSO4.2H2O)
Bonneville salt flats, Utah
Siliceous
 Chert (microcrystalline SiO2)
 Flint
 Jasper
 Agate
Jasper
Agate
Siliceous
 Chert (microcrystalline SiO2)
 Flint
 Jasper
 Agate
 Siliceous sediment
 Microfossils
Radiolarians
Bedded Chert
Siliceous
 Chert (microcrystalline SiO2)
 Flint
 Jasper
 Agate
 Siliceous sediment
 Microfossils
 Diagenetic
Chert nodules in Permian Kaibab Limestone. Grand Canyon, Arizona
Phosphorite
 Rich in phosphorous Ca10(PO4,CO3)6F2-3
 Phosphatic sediment (e.g., fish bones)
 Diagenetic
Why is this geology student so happy?
Bat guano, Slaughter Canyon Cave, NM
Transportation and deposition
Currents
• Air and water
• The faster the current the larger the particles
Settling
velocity
Sorting
Rounding
Sedimentary Structures
Large-scale features of sedimentary rocks that
result from physical and/or chemical processes
• Depositional
• Erosional
• Deformational
• Chemical (diagenetic)
Stratification
•Bedding
•Lamination
Laminated shale
1957, Charles Herbert
Depositional (Sedimentary)
Environments
A geographic location characterized by a particular
combination of geological processes and
environmental conditions
Diagenesis
All the changes sediment undergoes subsequent to deposition
and prior to metamorphism
Physical (mechanical) diagenesis
• Compaction
• Fracturing
• Ductile deformation
• Grain rearrangement
Chemical diagenesis
• Mineral precipitation (cementation)
• Dissolution
• Grain
• Cement
Lithification
The processes by which sediment is transformed into
sedimentary rock