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Sedimentary Rocks - PowerPoint PPT Presentation
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Sedimentary Rocks . Sedimentary rocks form when weathered sediment is deposited and is lithified. Review. What is: Sediment Weathering Deposition Lithification. Formation of Sedimentary Rocks. Lithification? The process of cementing and/or compacting sediment together.
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Sedimentary Rocks
- Sedimentary rocks form when weathered sediment is deposited and is lithified.
- Review. What is:
- Sediment
- Weathering
- Deposition
- Lithification
Formation of Sedimentary Rocks
- Lithification?
- The process of cementing and/or compacting sediment together.
- In the lab we did the other day (sand and food), which one represented compaction and which one represented cementation and why?
- What is an evaporite?
- Rocks that form after water has evaporated
Subclasses of Sedimentary Rocks
- What’s a subclass?
- Sedimentary rocks are sub-classified by the processes by which the rocks form and by the composition of the rocks.
- The three main sub-classes of sedimentary rocks are:
- Clastic
- Chemical
- Organic
Clastic Sedimentary Rock
- Clastic is Latin for “broken.”
- Clastic sedimentary rocksform when fragments of preexisting rocks are compacted or cemented together
- Clastic sedimentary rocks are classified by the size and shape of the sediments they contain.
Characteristics of Clastic Sediments
- The physical characteristics of sediments are determined by the how much weathering took place before lithification.
- Lots of weathering = smaller and rounded sediment
- Little weathering = larger and more angular sediment
Characteristics of Clastic Sediments
- The tendency for currents of air or water to separate sediments according to size is called sorting.
- Happens during weathering and erosion
- Well-sorted sediments, all of the grains are roughly the same size and shape.
- Poorly sorted sediment consists of grains that are many different sizes.
Chemical Sedimentary Rocks
- chemical sedimentary rocks form when minerals precipitate (solid out of liquid) when water evaporates.
- When water evaporates, the minerals that were dissolved in the water are left behind.
- What lab was this like?
- Rocks that form through evaporation are called evaporites. Rock gypsum and rock salt are common evaporites.
Organic Sedimentary Rocks
- organic sedimentary rocks form from the remains of plants or animals
- Coal and some limestones are examples of organic rocks (shell limestone, coquina, and chemical limestone).
- Organisms such as clams and coral make their shells from minerals. When the organism dies, their shells settle to the bottom of the ocean, accumulate, and are compacted and/or cemented to form limestone.
Organic Sedimentary Rocks
The diagram below shows the formation of organic limestone.
