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 6.13a,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 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 and 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.