Radiometric dating / Sediment accumulation

  • View
    50

  • Download
    0

Embed Size (px)

DESCRIPTION

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 - PowerPoint PPT Presentation

Transcript

  • Radiometric dating / Sediment accumulationI PrinciplesII AssumptionsIII 14C Production rateReservoir correctionsCirculation effectDeep-water ageIV 230Th - 234U Decay vs. productionConstant accumulation modelConstant 230Th flux model 230ThV 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 recorderBioturbation 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 approachesCoralsDeep-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 (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.