sedimentary rocks
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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.