Sedimentary Rocks

Sedimentary rocks form when sediment is compacted or cemented into solid rock

Fig. 3-2, p.46

The Rock Cycle

Weathering• Sediment becomes

smaller, more rounded and more sorted

• silicate minerals react with water to form clay (a new solid mineral) and dissolved ions (quartz is the exception)

• Weathering agents: water (most important), wind, gravity, glaciers

Rock Cycle Processes - Lithification

Lithification: Turning sediment into sedimentary rock

• Compaction : wet, buried sediment is squeezed by overlying sediments, causing it to become more solid.

• Cementation minerals dissolved during the weathering process precipitate and act as a cement, e.g. calcite, silica, and iron oxide.

Sedimentary Rock ClassificationBased on sediment source

• Detrital Sedimentary Rocks• Chemical Sedimentary Rocks

(which includes): – Inorganic Sedimentary Rocks–Biochemical Sedimentary Rocks–Organic Chemical Sedimentary Rocks

Grain size chart for detrital sedimentary rocks

Arkose: sandstone has significant feldspar content

• Detrital Sedimentary Rocks– composed of solid

sediment from weathered rocks

– conglomerate, sandstone, shale

• Chemical Sedimentary Rocks – Composed of minerals

precipitated from surface or ground water (chemical sediment)

– rock salt, rock gypsum

– Includes biochemical Sedimentary Rocks, composed of sediment of biological origin (e.g. shell fragments)

– Most common example is rock salt.

Coal• Different from other rocks because it is

composed of organic, not mineral material

• Stages in coal formation (in order)

1. Plant material

2. Peat

3. Lignite

4. Bituminous Coal

5. Anthracite (metamorphic)

Figure 6.13a,b

Figure 6.13b,c

Figure 6.13c,d

Sedimentary environments• Sedimentary rocks

contain evidence of past environments

• They provide information about climate (sediment size, presence or absence of water, sea level)

• Often contain fossils, which are indicators of both past climates and possible presence of fossil fuel.

Sedimentary environments• Sedimentary environment

or environment of deposition: A geographic setting where sediment is accumulating

• Determines the nature of the sediments that accumulate (grain size, grain shape, and other properties.)

• Today’s sedimentary rocks, tell us about past environments of deposition

Continental Sedimentary Environments

Dominated by erosion and deposition associated with – Streams– Wind (eolian

sandstones)

Continental Sedimentary Environments

• Glacial (morainal material)

• Alluvial fans (arkosic, feldspar-rich materials)

Shallow Marine Sedimentary Environments

Deep Marine Sedimentary Environments

Transitional Sedimentary Environments

• Tidal flats

• Lagoons

• Deltas

Sedimentary structures• Provide information useful in the

interpretation of Earth’s history• Types of sedimentary structures

• Strata, or beds (most characteristic of sedimentary rocks)

• Cross-bedding• Ripple marks• Mud cracks

Strata or layers

Cross-bedding in sediment

Cross-bedding in rock

Ripple marks

Mudcracks

The Carbon CycleThis is the process by which carbon moves throughout the

different “spheres” of the earth

Carbon Cycle – Hydrosphere and Biosphere

In the hydrosphere, CO2

– dissolves in seawater– is released by organic matter and carbonate rocks

In the biosphere, CO2 accumulates from:– photosynthesis of plant organisms– uptake by land and marine organisms to make shells

or bones

Carbon Cycle – Atmosphere and Geosphere

In the atmosphere, CO2 accumulates from:

– burning of fossil fuels– volcanic processes– weathering of carbonate rock– burning and decay of biomass – respiration

In the geosphere, CO2 accumulates as carbonate sediments and rocks.