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Earth Systems 3209. Reference: Chapters 2, 3, 6, 7; Appendix A & B. Unit: 3 Earth’s Materials. Unit 3: Topic 4.2 . Classification of Sedimentary Rocks - Overview. Focus on . . . identifying and providing an overview of the three classifications of sedimentary rocks.
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Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials
Unit 3: Topic 4.2 Classification of Sedimentary Rocks - Overview Focus on . . . • identifying and providing an overview of the three classifications of sedimentary rocks.
Classification of Sedimentary Rocks • Sedimentary rocks usually originate in water environments, either oceans, lakes, or rivers. • Sedimentary rocks are grouped as: • Clastic/Detrital2) Chemical3) Biochemical • Clastic and Chemical are the most common sedimentary rocks. They make up the majority of sedimentary rocks found on Earth’s surface. Text Reference: pages 159-173
Three Classes of Sedimentary Rocks • Clastic/Detritalsedimentary rocks • Form when weathered materials called sediment, is transported, deposited and lithified by compaction and cementing to form solid rock. • Chemical sedimentary rocks • Form when soluble materials get dissolved and transported to water environments where it then precipitates/evaporates to form solid rock. • Biochemical sedimentary rocks • Form as a result of once living organisms accumulating to form solid rock.
1) Clastic Sedimentary Rocks • Consist of solid particles from weathered rocks. These rock fragments include pebbles, sand, silt and clay. • Rock fragments are a result of physical weathering. • These rocks usually form in water environments such as, rivers, lakes, oceans, but can also form in deserts.
1) Clastic Sedimentary Rocks • Geologist use particle size to distinguish between clastic sedimentary rocks, as seen in the table below.
Sediment – Particle Size • This figure shows how clastic sediment of various sizes will, after compaction and cementation, form different types of clastic/detritalsedimentary rocks. • The process of sediment turning into rock is called lithification.
2) Chemical Sedimentary Rocks • These rocks form as a result of chemical weathering dissolving chemicals and transporting it in solution. When conditions are right, these dissolved chemicals change back into a solid through the processes of precipitation and evaporation. • Precipitation: • Process where chemicals dissolved on solution, fall out of solution and forms a solid material. Most common in shallow water environments. • Evaporation: • Process where there is a change in state from a liquid to a gas. Chemicals dissolved in the liquid (water) are left behind as a solid material.
2) Chemical Sedimentary Rocks • These rocks usually form in water environments such as lakes and shallow seas or oceans. • Some examples of chemical sedimentary rocks include; • Limestone (Calcite) - (form by precipitation) • Rock Gypsum - (form by precipitation and evaporation) • Rock salt (Halite) – (from by evaporation) • Note:Evaporation and Precipitation often work together. As water evaporates, chemicals in solution will precipitate.Example: Rock Salt (Halite).
3) Biochemical Sedimentary Rocks • Precipitation may occur as a result of physical processes, or indirectly through life processes of water-dwelling organisms. Sedimentary rocks formed in this way are referred to as Biochemical. • Many organisms excrete dissolved minerals to form shells and when theydie the shells accumulate on the seafloor and form a rock called Coquina.
3) Biochemical Sedimentary Rocks • Biochemical • Sedimentary rock created when organisms use materials dissolved in air or water to build their tissue. • Examples include: • Coquina • Chaulk • Chert • Limestone (Coral) • Coal
3) Biochemical Sedimentary Rocks • Biochemical • Sedimentary rock created when organisms use materials dissolved in air or water to build their tissue. • A common organicbiochemical rock is coal, which forms when plant material in water saturated environments (swamps) die and accumulate to form peat. As peat is buried it compresses and eventually changes to form coal.
Example 1: Which agent of erosion shaped the particles that formed the rock in the diagram to the right? glacial ice (B) mass movement (C) running water (D) wind Which best describes gravel, sand and clay? (A) cements (B) organic remains (C) chemical precipitates (D) sediments
Example 2: Which table below correctly classifies the rocks?
Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Citing two differences, compare clastic and chemical sedimentary rocks.
Solutions . . . Answer: Differences are seen because clastic and chemical sediments are formed by different processes. Clastic sediment forms when pre-existing rocks are weathered by a physical weathering and are lithified to form solid rock. Whereas, chemical sediment forms when chemical weathering dissolves rock material in solution and precipitates the chemical to form solid rock. Clasticrocks are generally classified by particle size, whereas, chemical rocks are classified by its chemical composition.
Summary . . . Overview of Points covered: • Sedimentary Rocks can be classified three ways: • Clasticor Detrital-- contain particles • Chemical-- contain chemicals • Biochemical-- contain once living material
