Sedimentary Rocks 1
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Transcript of Sedimentary Rocks 1
Sedimentary Rocks
What are they?
• Sedimentary rocks are a result of: a) the destruction of rocks, b) organic/biochem. reactions, or c) chemical precipitation
Different sources
• Detrital – breaking of rocks
Different sources
• Biochemical (organic)
Different sources
• Chemical
Chemical – Rock Salt
Biochemical/organic – Coquina
Detrital - Arkose
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
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
Roundness
SortingPoorly Moderate Well
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
Specific Environments
• Detrital TerrigenousSed. Rocks in the cycle
• Biochemical Swamp/Shallow Marine• Evaporites Precipitation• Crystalline Detrital Rock
Processes
• Chemical/Mechanical breakdown• Diagenesis/Cementation• Precipitation• Evaporation
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?
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