Sedimentary Rocks

1. Sedimentary Rocks

2. Sedimentary rocks form when sediment is compacted or cemented into solid rock Fig. 3-2, p.46

3. The Rock Cycle

4. Weathering • Sediment becomes smaller, more rounded and more sorted • silicate minerals react with water to form clay (a new solid mineral) and dissolved ions (quartz is the exception) • Weathering agents: water (most important), wind, gravity, glaciers

5. Rock Cycle Processes - Lithification

6. Lithification: Turning sediment into sedimentary rock • Compaction : wet, buried sediment is squeezed by overlying sediments, causing it to become more solid. • Cementation minerals dissolved during the weathering process precipitate and act as a cement, e.g. calcite, silica, and iron oxide.

7. Sedimentary Rock ClassificationBased on sediment source • Detrital Sedimentary Rocks • Chemical Sedimentary Rocks (which includes): • Inorganic Sedimentary Rocks • Biochemical Sedimentary Rocks • Organic Chemical Sedimentary Rocks

8. Grain size chart for detrital sedimentary rocks Arkose: sandstone has significant feldspar content

9. Detrital Sedimentary Rocks • composed of solid sediment from weathered rocks • conglomerate, sandstone, shale

11. Chemical Sedimentary Rocks • Composed of minerals precipitated from surface or ground water (chemical sediment) • rock salt, rock gypsum • Includes biochemical Sedimentary Rocks, composed of sediment of biological origin (e.g. shell fragments) • Most common example is rock salt.

12. Coal • Different from other rocks because it is composed of organic, not mineral material • Stages in coal formation (in order) 1. Plant material 2. Peat 3. Lignite 4. Bituminous Coal 5. Anthracite (metamorphic)

13. Figure 6.13a,b

14. Figure 6.13b,c

15. Figure 6.13c,d

18. Sedimentary environments • Sedimentary rocks contain evidence of past environments • They provide information about climate (sediment size, presence or absence of water, sea level) • Often contain fossils, which are indicators of both past climates and possible presence of fossil fuel.

19. Sedimentary environments • Sedimentary environment or environment of deposition: A geographic setting where sediment is accumulating • Determines the nature of the sediments that accumulate (grain size, grain shape, and other properties.) • Today’s sedimentary rocks, tell us about past environments of deposition

20. Continental Sedimentary Environments Dominated by erosion and deposition associated with • Streams • Wind (eolian sandstones)

21. Continental Sedimentary Environments • Glacial (morainal material) • Alluvial fans (arkosic, feldspar-rich materials)

22. Shallow Marine Sedimentary Environments

23. Deep Marine Sedimentary Environments

24. Transitional Sedimentary Environments • Tidal flats • Lagoons • Deltas

25. Sedimentary structures • Provide information useful in the interpretation of Earth’s history • Types of sedimentary structures • Strata, or beds (most characteristic of sedimentary rocks) • Cross-bedding • Ripple marks • Mud cracks

26. Strata or layers

27. Cross-bedding in sediment

28. Cross-bedding in rock

29. Ripple marks

30. Mudcracks

31. The Carbon CycleThis is the process by which carbon moves throughout the different “spheres” of the earth

32. Carbon Cycle – Hydrosphere and Biosphere In the hydrosphere, CO2 • dissolves in seawater • is released by organic matter and carbonate rocks In the biosphere, CO2 accumulates from: • photosynthesis of plant organisms • uptake by land and marine organisms to make shells or bones

33. Carbon Cycle – Atmosphere and Geosphere In the atmosphere, CO2 accumulates from: • burning of fossil fuels • volcanic processes • weathering of carbonate rock • burning and decay of biomass • respiration In the geosphere, CO2 accumulates as carbonate sediments and rocks.