sedimentary rocks 1
DESCRIPTION
Sed rocks lab class powerpointTRANSCRIPT
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Sedimentary Rocks
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What are they?
• Sedimentary rocks are a result of: a) the destruction of rocks, b) organic/biochem. reactions, or c) chemical precipitation
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Different sources
• Detrital – breaking of rocks
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Different sources
• Biochemical (organic)
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Different sources
• Chemical
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Chemical – Rock Salt
Biochemical/organic – Coquina
Detrital - Arkose
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Identifying a sed. rock - Texture• Texture – description of parts of the rock and
their size, shape and arrangement; determines source
• What to look for: size, roundness, sorting
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Grain Size• Are the grains:
(a) larger than 2 mm (gravel size)(b) sand size; 1/16 – 2 mm (visible)(c) mud/silt size; <1/16 mm (not visible)(d) crystalline/microcrystalline – resp. crystals are visible/ not
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Roundness
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SortingPoorly Moderate Well
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Determining the origin (source)
• Specific Environments1. Terrigenous (fluvial, deltaic, aeolian, etc.)2. Swamp/lagoon3. Shallow marine
• Processes1. chemical and mechanical breakdown2. diagenesis/cementation3. precipitation4. evaporation
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Specific Environments
• Detrital TerrigenousSed. Rocks in the cycle
• Biochemical Swamp/Shallow Marine• Evaporites Precipitation• Crystalline Detrital Rock
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Processes
• Chemical/Mechanical breakdown• Diagenesis/Cementation• Precipitation• Evaporation
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Finding the source
• Use interpretive skills!• Detrital use texture to determine maturity;
How far from the source?• Biochemical/organic What is it made out
of? Where would you find these organisms?• Chemical How did it form? What
environments most likely would you find them in?
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Examples Rock salt, evaporitive:
formed in a saline body of water
Peat, biochemical/organic:dark mud, plant fragments indicates it was formed in a swamp environment