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Radiometric dating / Sediment accumulation

Radiometric dating / Sediment accumulation. I Principles. IV 230 Th - 234 U Decay vs. production Constant accumulation model Constant 230 Th flux model 230 Th. II Assumptions. V Other… Radiometric (Ar-Ar) Annual (varves) Cyclical (orbital). III 14 C

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Radiometric dating / Sediment accumulation

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  1. Radiometric dating / Sediment accumulation IPrinciples • IV230Th - 234U • Decay vs. production • Constant accumulation model • Constant 230Th flux model 230Th IIAssumptions • VOther… • Radiometric (Ar-Ar) • Annual (varves) • Cyclical (orbital) • III14C • Production rate • Reservoir corrections • Circulation effect • Deep-water age

  2. Dating sediment goal Establish age-depth relationship

  3. Terminology Parent Daughter Isotopes Stable Radioactive alpha, beta, gamma decay

  4. Radioactive decay Spontaneous emission Nuclear transformation Loss of parent Growth of daughter

  5. Definitions Decay constant Activity Half life Mean life

  6. Application Balance of Resolution vs. longevity 14C useful for last climate cycle.

  7. Reporting convention Time zero = 1950 Half life = 5730 y del notation vs. stand.

  8. Definitions Decay constant Activity Half life Mean life

  9. Age and accumulation Assumptions Uncertainty

  10. Dating sediment goal Establish age-depth relationship

  11. Bioturbation Sediment imperfect recorder Bioturbation example of filter

  12. Reservoir effect Transfer from one reservoir to another takes time.

  13. Variable pathways Sources Sinks

  14. Different scales Radiocarbon and calendar

  15. Solar variabiluty Sunspot cycles and 14C production

  16. Age offsets Long-term trend

  17. Age offsets Ocean and climate Influences possible.

  18. Comparisons Independent chronologies allow test of influences. Hughen et al.

  19. Age offsets

  20. Evolving production Atmospheric 14C and magnetic field inverse.

  21. 14C through time Complications of Carbon cycle, physical and chemical cycling.

  22. Ocean circulation Influence on apparent age

  23. Age “plateaus”

  24. Age anomalies Modeling ocean and production variations.

  25. Uranium series Absolute chronology?

  26. Parent decay to stable daughter

  27. Secular equilibrium Between long half- life parent and shorter half-live daughter

  28. Uranium series Different approaches Corals Deep-sea sediments

  29. Uranium series Downcore approach

  30. Uranium series Assume constant deposition, estimate rate.

  31. Uranium series Second approach. Assume constant flux of decay product, estimate instantaneous rates of sedimentation.

  32. Uranium series Reasonable assumption

  33. Uranium series Integrated approach (Sackett’s method).

  34. Uranium series Test of (Sackett’s method).

  35. Uranium series Test of Sackett’s method.

  36. Uranium series Works for special case.

  37. Extraterrestrial IDPs New 3He approach.

  38. Ar - Ar method Dating tool for longer time, lower resolution.

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