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Understanding Sedimentary Rocks: Formation and Features

Explore the processes of weathering, erosion, and lithification that lead to sedimentary rock formation. Learn about the various types of sedimentary rocks, their features, and the importance of fossils. Discover the role of deposition, compaction, and cementation in lithification.

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Understanding Sedimentary Rocks: Formation and Features

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  1. 6.1/6.2 Guided Notes Hybrid

  2. Weathering and Erosion • Sediments: small pieces of rock that are moved and deposited by water, wind and gravity

  3. Lithification: • Sediment is deposited in low areas such as valleys and ocean basins • Bottom layers are subjected to intense pressure and temperatures • This process is called lithification: THE PHYSICAL AND CHEMICAL PROCESSES THAT TRANSFORM SEDIMENT INTO SEDIMENTARY ROCK

  4. Erosion: removal and transport of sediment Agents of erosion: • Wind • Moving water • Gravity • Glaciers

  5. Sedimentary Features: • Sedimentary rock tells geologists the history of the area • BEDDING: predominant feature of sedimentary rock is the horizontal layering • Feature results from the way water or wind causes the sediment to settle out • Two types of bedding

  6. Bedding Type #1: Graded Bedding • Bedding in which heavier and coarser particles are located near the bottom of the sedimentary rock

  7. Bedding Type #2: Cross-Bedding • Inclined layers of sediment deposited along a horizontal surface

  8. Mud Cracks and Ripple Marks • Mud (usually forms in hexagonal plates) cracks and sediments seep between the mud plates • The sediments build up over time forming sedimentary rock • Ripple Marks: • Evidence that the sediment was formerly moved by wave action

  9. Fossils • The best known feature of sedimentary rock is the propensity to find fossils in it • During lithification the animal’s parts (like the shell) can be replaced by minerals and turned to rock which make up a fossil

  10. Types of Sedimentary Rock • Clastic / Detrital – made up of solid particles (gravel, sand, silt and clay) derived from preexisting rocks through weathering • Chemical – sedimentary rocks that result from inorganic chemical processes or from the chemical activities of organisms

  11. Clastic / Detrital Sedimentary Rocks • Coarse-grained • Gravel sized fragments • Types of rock formed: conglomerate (rounded gravel), breccia (angular gravel) • Formed by high-energy flows of water • Medium-grained • Sand fragments • Type of rock formed: sandstone • Formed by stream & river channels, beaches, deserts • Importance: due to pore spacing, fluids can move through and thus hold reservoirs of oil, natural gas, and groundwater • Fine-grained • Silt and mud fragments • Type of rock formed: siltstone, shale, mudstone • Importance: low porosity resulting in a barrier to movement of groundwater & oil.

  12. Chemical Sedimentary Rock • Inorganic Sedimentary Rock • Evaporite – form as a result of crystal grains precipitating our of a supersaturated body of water • Type of rock formed: rock gypsum (made up of the mineral gypsum) & rock salt (made up of the mineral halite)

  13. Chemical Sedimentary Rock • Biochemical – form as a result of the chemical processes of organisms, many times the remains of once-living plants and/or animals. • Types of rock formed: limestone, chert, and coal. • Form in shallow-water, swamp, and coastal environments chert coal

  14. Importance of Sedimentary Rock • Provide historical timeline for area. Leaves a ‘footprint’ of all that’s come before us. • Past plants and animals • Bedrock • Ancient rivers, lakes and shorelines • Provides resources • Oil, natural gas, and coal • Building materials • Uranium • Phosphate and iron

  15. Deposition • Occurs when transported sediments are deposited on the ground or sink to the bottom of a body of water • Settles with the largest grains at the bottom of the layering and the smallest grains at the top

  16. Lithification part 1 COMPACTION • The weight forces the sediment grains to get closer and closer together causing physical changes to occur • Mud can contain up to 60% water that gets squeezed out • Sand does not compact as much as mud does because sand is mostly quartz • Grain to grain contact in sand forms a supporting framework that maintains open space between the grains

  17. Lithification part 2 CEMENTATION • Minerals like calcite CaCO3 and iron oxide Fe2O3 flow through the open spaces left by compaction • The minerals linger and cement the grains together forming sedimentary rock

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