Sedimentary Rocks - PowerPoint PPT Presentation

• Sedimentary rocks form when weathered sediment is deposited and is lithified.
• Review. What is:
• Sediment
• Weathering
• Deposition
• Lithification

• 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

• 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 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.

• 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

• 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 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 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.

The diagram below shows the formation of organic limestone.