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Geologic Time Physical Geology Chapter 8

Geologic Time Physical Geology Chapter 8. Tim Horner, CSUS Geology Department. Dating rocks: Relative dating: Puts events in order Doesn’t necessarily give an exact age Absolute (Numerical) dating:

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Geologic Time Physical Geology Chapter 8

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  1. Geologic TimePhysical Geology Chapter 8 Tim Horner, CSUS Geology Department

  2. Dating rocks:Relative dating: Puts events in order Doesn’t necessarily give an exact ageAbsolute (Numerical) dating: Used principles of radioactive decay Assigns a numerical age to a rock Only works for certain rock types

  3. Figure 8.1

  4. Figure 8.2 Step 1) Rocks are deposited in the ocean

  5. Figure 8.3 • Step 2) Sequence of rocks is deposited • (oldest first): • Lutgrad Fm • Birkland Fm • Tarburg Fm • Leet Junction Fm

  6. Figure 8.4 Step 3) Sequence is intruded, with contact metamorphism at edges of pluton

  7. Figure 8.5 Step 4) Sequence is tilted, top of new surface is eroded

  8. Figure 8.1

  9. Figure 8.6 Step 5) Area subsided, was covered by ocean, Larsonton Fm was deposited

  10. Figure 8.8 Step 6) Larsonton Fm was intruded by dike

  11. Figure 8.9 Step 7) Erode material (expose dike)

  12. Figure 8.10 Step 8) Subsidence, deposit more marine sediments (Foster City Fm) above unconformity unconformity

  13. Figure 8.11 Step 9) Raise entire sequence above sea level, begin downcutting by modern stream

  14. Figure 8.1 Final product:

  15. Figure 8.14a-d Formation of angular unconformity

  16. Figure 8.14e Angular unconformity

  17. Figure 8.14f Angular unconformity

  18. Figure 8.12 Non-conformity

  19. Figure 8.15 Non-conformity

  20. Figure 8.13 Disconformity

  21. Figure 8.16 Lithologic correlation- tracing beds

  22. Figure 8.17 Lithologic correlation- similar rock sequences (Gondwana Sequence)

  23. Figure 8.18 Correlation by fossils

  24. Table 8.2 Geologic time scale

  25. Figure 8.19

  26. Table 8.3 Commonly used radiogenic isotopes:

  27. Figure 8.22 Radiogenic dating: parent and daughter isotopes

  28. Figure 8.21

  29. Figure 8.23 Radiogenic dating brackets events

  30. Figure 8.24 Geologic time scale, with absolute dates

  31. Figure 8.25 Absolute time scale

  32. Figure 8.20 Numeric (absolute) dating Uses radiogenic isotopes Decay rates are known, constant 3 decay methods: Alpha decay Beta decay Electron capture

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