Sedimentary Rocks Sedimentary rocks form when sediment is

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 Classification Based 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. 13 a, b

Figure 6. 13 b, c

Figure 6. 13 c, 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, feldsparrich 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 Cycle This is the process by which carbon moves throughout the different “spheres” of the earth

Carbon Cycle – Hydrosphere and Biosphere In the hydrosphere, CO 2 – dissolves in seawater – is released by organic matter and carbonate rocks In the biosphere, CO 2 accumulates from: – photosynthesis of plant organisms – uptake by land marine organisms to make shells or bones

Carbon Cycle – Atmosphere and Geosphere In the atmosphere, CO 2 accumulates from: – burning of fossil fuels – volcanic processes – weathering of carbonate rock – burning and decay of biomass – respiration In the geosphere, CO 2 accumulates as carbonate sediments and rocks.