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SEDIMENTARY ROCKS • Sedimentary rocks form from various types of sediment. • Sedimentary rocks make up 90% of SURFACE rocks and only about 1% of Earth’s crust.
How are Sedimentary Rocks Formed • Sedimentary rock forms when sediments are combined to form solid rock • “Lithification” is the fancy name forming rocks. • Sedimentary rock is formed in two ways: – Compaction • Formed by pressure compacting the sediments together AND/OR – Cementation • Pressure forces water out of the sediments, the dissolved mineral crystallize, cementing the sediments together
Compaction and Cementation of Clastic Sediment into Rock “Overburden” is extra stuff on top. More sediment, a continent, whatever. Overburden
Three Kinds of Sedimentary Rocks • 1. Clastic – fragments of other rocks. For example: shale, sandstone, conglomerate • 2. Crystalline – formed from mineral grains that fall out of solution by chemical action or evaporation. For example: Rock salt and chemical limestone. • 3. Bioclastic – formed from remains of plants or animals. For example: Coal and limestone from shells (coquina).
How are Clastic Sedimentary Rocks formed • Sediment is deposited and then goes through the process of lithification (forming sediment into sedimentary rocks)
How are Clastic Sedimentary Rocks formed Weathering Erosion Deposition Lithification
Clastic Sedimentary Rocks • Clastic sedimentary rocks are characterized based on their grain size.
How are Clastic Sedimentary Rocks formed. • Grain sizes vary from Coarse (pebbles, cobbles, boulders) to Medium (sand) to Fine (silt and clay).
Grain Sizes Boulders Cobbles Coarse Gravel Fine Gravel Coarse / Medium Sand Fine Sand – Powdered Sugar Silt - Powder
How Does The Sediment Get Sorted Into Different Sizes? • Running water (rivers, streams, creeks) pick up sediment and carry it along its travels. • The faster the water is moving, the larger the particle that can be carried, and vice-versa. • When a river hits a larger body of water, like a lake or ocean, it’s like hitting a brick wall. This results in the river “dumping it’s load” – dropping all the sediment it’s been carrying. • The sediment gets dumped according to size!
How Does The Sediment Get Sorted Into Different Sizes? • The bigger sediment gets deposited FIRST, since it’s bigger, heavier and sinks first. • Then, the sediment gets gradually SMALLER the farther you go from where the river hits the lake or ocean. • Therefore, coarse clastic rocks get made where the larger sediment gets deposited and the medium to fine clastic rocks get made further away from that point.
Clastic Sedimentary Rocks Conglomerate – made of pebbles and/or cobbles cemented together by sand, silt and clay. Coarsegrained Sandstone – sand that has been cemented together. Medium-grained Shale – made from clay. Finegrained
Crystalline Sedimentary Rocks • Also called chemical sedimentary rocks. • Chemical action or evaporation causes minerals to drop out of solution. • This process creates chemical or crystalline sedimentary rocks. • For example: Calcite will precipitate out of water and build-up to form chemical limestone (it will fizz with acid since it has calcite in it!)
Crystalline (Chemical) Sedimentary Rocks Gypsum Rock – made when the mineral gypsum precipitates out of water. Chemical Limestone
What happens when salty water evaporates and just salt is left behind? Bonneville Salt Flats of the Great Salt Lake, Utah. The lake bed is covered with rock salt which gives it the white color. The salt is mined by the Morton Salt Company.
Bioclastic (Organic) Sedimentary Rocks • Also called Organic sedimentary rocks. • Formed from once-living things like plants and animals. • For example: Plants die and decay and form coal. • Another example: Shells can get broken up and cemented back together to form organic limestone (also called coquina).
Bioclastic (Organic) Sedimentary Rocks Coal Organic Limestone or Coquina
Answers 1. Define Clastic. Made from fragments of other rocks 2. Define bioclastic. Formed from remains of plants or animals 3. What type of rock is made of particle. 05 cm? Sandstone 4. What type of rock is made of particle. 1 cm? Sandstone 5. What is the chemical composition of bituminous coal? Carbon