Radiometric dating / Sediment accumulation I Principles II Assumptions III 14 C Production rate Reservoir corrections Circulation effect Deep-water age IV 230 Th U Decay vs. production Constant accumulation model Constant 230 Th flux model 230 Th V Other… Radiometric (Ar-Ar) Annual (varves) Cyclical (orbital)
Dating sediment goal Establish age-depth relationship
Terminology Parent Daughter Isotopes Stable Radioactive alpha, beta, gamma decay
Radioactive decay Spontaneous emission Nuclear transformation Loss of parent Growth of daughter
Definitions Decay constant Activity Half life Mean life
Application Balance of Resolution vs. longevity 14 C useful for last climate cycle.
Reporting convention Time zero = 1950 Half life = 5730 y del notation vs. stand.
Definitions Decay constant Activity Half life Mean life
Age and accumulation Assumptions Uncertainty
Dating sediment goal Establish age-depth relationship
Bioturbation Sediment imperfect recorder Bioturbation example of filter
Reservoir effect Transfer from one reservoir to another takes time.
Variable pathways Sources Sinks
Different scales Radiocarbon and calendar
Solar variabiluty Sunspot cycles and 14 C production
Age offsets Long-term trend
Age offsets Ocean and climate Influences possible.
Hughen et al. Comparisons Independent chronologies allow test of influences.
Age offsets
Evolving production Atmospheric 14 C and magnetic field inverse.
14 C through time Complications of Carbon cycle, physical and chemical cycling.
Ocean circulation Influence on apparent age
Age plateaus
Age anomalies Modeling ocean and production variations.
Uranium series Absolute chronology?
Parent decay to stable daughter
Secular equilibrium Between long half- life parent and shorter half-live daughter
Uranium series Different approaches 1.Corals 2.Deep-sea sediments
Uranium series Downcore approach
Uranium series Assume constant deposition, 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 (Sacketts method).
Uranium series Test of (Sacketts method).
Uranium series Test of Sacketts method.
Uranium series Works for special case.
Extraterrestrial IDPs New 3He approach.
Ar - Ar method Dating tool for longer time, lower resolution.