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Sediments and Sedimentary Rocks Chapter 5

Sediments and Sedimentary Rocks Chapter 5

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Sediments and Sedimentary Rocks Chapter 5

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  1. Sediments and Sedimentary RocksChapter 5

  2. Concepts you will need to know for the exams • Weathering • Erosion • Transportation • Sorting • Angularity • Sedimentary environments, • Cross-bedding (sedimentary structures) • Bioturbation, bedding sequences, diagenesis • Classes of sediments and sedimentary rock: • -based on grain size • -based on chemical composition, e.g., carbonate rocks ("carbonates") and evaporitic rocks ("evaporites")

  3. Lecture Outline • Sedimentary rocks • 2. Your sedimentary environment and Burial and diagenesis • 3. Interpretation of clastic texture • 4. Sedimentary structures • 5. Sedimentary Rock classification

  4. 1. Sedimentary Rocks • Cover most of the land surface and seafloor • Your physical geography determines the dominant process at work in the sedimentary rock cycle • e.g. (1) Mountains => weathering and/or erosion • e.g., (2) Southern Louisiana => • e.g., (3) offshore Louisiana =>

  5. 1. Sedimentary Rocks • Cover most of the land surface and seafloor • Your physical geography determines the dominant process at work in the sedimentary rock cycle • e.g. (1) Mountains => weathering and/or erosion • e.g., (2) Southern Louisiana => transportation or deposition or erosion • e.g., (3) offshore Louisiana =>

  6. 1. Sedimentary Rocks • Cover most of the land surface and seafloor • Your physical geography determines the dominant process at work in the sedimentary rock cycle • e.g. (1) Mountains => weathering and/or erosion • e.g., (2) Southern Louisiana => transportation or deposition or erosion • e.g., (3) offshore Louisiana => erosion or sedimentation

  7. erosion weathering transportation Erosion includes BOTH weathering and transportation

  8. Sedimentary rocks are typically layered, (although layering is not diagnostic of only sedimentary rocks)

  9. Lecture Outline • Sedimentary rocks; surface processes • 2. Your sedimentary environment and Burial and diagenesis • 3. Interpretation of clastic texture • 4. Sedimentary structures • 5. Sedimentary Rock classification

  10. A sedimentary environment is a geographic location that has a peculiar combination of geological processes

  11. Walther’s Rule (1894) “The different (sedimentary) rocks (types) were formed beside each other in space, but in a crustal profile we see them lying on top of each other….”

  12. Bedding sequences--- are successions of rock ( in a vertical profile) that help geologists work out the past environment

  13. Where do you live? • What dominant sedimentary process is at work where you live?

  14. If deposition is the dominant process, e.g., offshore Lousiana then rocks are in the process of being formed: Diagnesis includes (1) compaction = volume loss (mechanical squeezing) and is accompanied by dewatering (= water loss) (by chemical or physical means) (2) changes in mineral composition (chemical process with heat and or fluids) (3) cementation (physical) If a sediment eventually becomes a rock we say it is lithified.

  15. DIAGENESIS compaction

  16. DIAGENESIS compaction dewatering

  17. DIAGENESIS compaction dewatering Cementation & mineral changes

  18. Lecture Outline • Sedimentary rocks; surface processes • 2. Your sedimentary environment and Burial and diagenesis • 3. Interpretation of clastic texture • 4. Sedimentary structures • 5. Chemical and biological classification

  19. Geological FUZZY rulesfor determining degree of weathering and transport a rock or sediment has experienced respectively

  20. (1) Product composition

  21. (2) Degree of sorting

  22. Sorting is a measure of how similar grain sizes are within a sediment or rock and tells us about the relative strength of the current before it dropped (deposited) it cargo. • In a current of water or air, the larger and denser grains fall faster than the smaller grains. That is, for the same density, size determines settling velocity.

  23. (3) Angularity or roundness (antonym) is a measure of the distance of transportation

  24. Lecture Outline • Sedimentary rocks; surface processes • 2. Your sedimentary environment and Burial and diagenesis • 3. Interpretation of clastic texture • 4. Sedimentary structures • 5. Chemical and biological classification

  25. Cross-bedding Cross-bedding: sets of bedded material within rock layers that are inclined at angles as large as 35 degrees from the horizontal. These latter indicate wind-blown conditions in either a desert or a beach.

  26. 2 directions of fluid movement

  27. Fossil example of the past activity of organisms mixing sediment --- an example of fossil BIOTURBATION

  28. Lecture Outline • Sedimentary rocks; surface processes • 2. Your sedimentary environment and Burial and diagenesis • 3. Interpretation of clastic texture • 4. Sedimentary structures • 5. Sedimentary Rock classification

  29. Three types of sedimentary Rocks • Clastic • Biochemical • Chemical

  30. Major Classes of sediments and sedimentary rocks For clastic sedimentary rocks there is a classification scheme based on the SIZE of their clasts, (or rock fragments) that comprise them.

  31. Clst size indicates ancient relative current velocity weak moderate >=1.8 km/hr (strong currents)