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