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

Bat guano, Slaughter Canyon Cave, NM

Why is this geology student so happy?

Transportation and deposition

Currents

• Air and water• The faster the current the larger the

particles

Settling velocity

Sorting

Rounding

Sedimentary Structures

• Depositional• Erosional • Deformational• Chemical (diagenetic)

Large-scale features of sedimentary rocks that result from physical and/or chemical processes

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