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.