sedimentary rocks. sedimentary rocks form when sediment is compacted or cemented into solid rock...
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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
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
• 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)
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)
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
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