Reading: Chapter 4 Lecture 6. Formation of the Moon, Absolute Ages, Radiometric Dating.
Radiometric dating / Sediment accumulation I Principles II Assumptions III 14 C Production rate...
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Transcript of Radiometric dating / Sediment accumulation I Principles II Assumptions III 14 C Production rate...
Radiometric dating / Sediment accumulation
I Principles
II Assumptions
III 14C Production rate
Reservoir correctionsCirculation effectDeep-water age
IV 230Th - 234U Decay vs. production
Constant accumulation modelConstant 230Th flux model 230Th
V Other… Radiometric (Ar-Ar)
Annual (varves)Cyclical (orbital)
Dating sediment goal
Establish age-depth relationship
Terminology
ParentDaughterIsotopesStableRadioactivealpha, beta, gammadecay
Radioactive decay
Spontaneous emissionNuclear transformationLoss of parentGrowth of daughter
Definitions
Decay constantActivityHalf lifeMean life
Application
Balance of Resolution vs. longevity
14C useful for lastclimate cycle.
Reporting convention
Time zero = 1950Half life = 5730 ydel notation vs. stand.
Definitions
Decay constantActivityHalf lifeMean life
Age and accumulation
AssumptionsUncertainty
Dating sediment goal
Establish age-depth relationship
Bioturbation
Sediment imperfect recorder
Bioturbation example of filter
Reservoir effect
Transfer from onereservoir to anothertakes time.
Variable pathways
SourcesSinks
Different scales
Radiocarbon and calendar
Solar variabiluty
Sunspot cycles and14C production
Age offsets
Long-term trend
Age offsets
Ocean and climateInfluences possible.
Hughen et al.
Comparisons
Independent chronologies allow test of influences.
Age offsets
Evolving production
Atmospheric 14C andmagnetic field inverse.
14C through time
Complications ofCarbon cycle, physical and chemical cycling.
Ocean circulationInfluence on apparent age
Age “plateaus”
Age anomalies
Modeling ocean andproduction variations.
Uranium series
Absolute chronology?
Parent decay to stable daughter
Secular equilibrium
Between long half-life parent and shorterhalf-live daughter
Uranium series
Different approaches1. Corals2. Deep-sea sediments
Uranium series
Downcore approach
Uranium series
Assume constantdeposition, estimate rate.
Uranium series
Second approach.Assume constant flux of decay product, estimate instantaneous rates of sedimentation.
Uranium series
Reasonable assumption
Uranium series
Integrated approach (Sackett’s method).
Uranium series
Test of (Sackett’s method).
Uranium series
Test of Sackett’s method.
Uranium series
Works for special case.
Extraterrestrial IDPs
New 3He approach.
Ar - Ar method
Dating tool for longer time, lower resolution.