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Problems Related to Interplanetary Matter (1961) / Chapter Skim
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RADIUM-URANIUM AGE DETERMINATIONS ON MARINE SHELLS
Pages 96-101

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From page 96...
... A method originally conceived by Potratz based on inequilibrium in the U series may be suitable for this purpose. This method depends upon the observation that the ratio of A 230^ 238 in recently formed marine carbonates generally seems to be quite low (<0.
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From page 97...
... Measurements have been made on three types of marine carbonates: contemporary shells; shells and corals of known radiocarbon age; carbonates sufficiently old so that radioactive equilibrium should have been attained. A check of the analytical methods on uranium and radium standard samples indicates that standard deviations are <10 percent (U)
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From page 98...
... The data on British Columbia and Spitsbergen shells generally show reasonably good agreement, when the first 10-30 percent of the sample is neglected. A puzzling feature is the systematic decrease, often by large factors, in the Ra226 content during the first stages of the progressive acid leach.
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From page 99...
... 5 5.9±0. 2 TABLE 4 Results on British Columbia Shells Sample # Fraction % Ra226 U238 Ra-U Age C" Ra226 Age (103y)
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From page 100...
... The discrepancy between Ra-U and C14 ages for sample 572-C (Table 5) is probably due to inseparable contamination with modern Stratigraphically, 572-C is certainly considerably older than 572-A or 572-B and may be from a previous interglacial period, which would agree with the Ra-U ages.
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From page 101...
... Ages obtained range from 100, 000 years to 134, 000 years, which is in reasonable agreement with dates for the last interglacial age estimated from extrapolations of sedimentation rates for ocean cores. In conclusion, although the Ra-U method may not be capable of providing a precise independent check of the Cl4 ages, it is promising as a means of extending the range of age measurements in marine carbonates to perhaps 200, 000 years.
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Key Terms

  • independent check
  • interglacial age
  • shells sample
  • potratz based
  • standard deviations

  • miscellaneous shell
  • originally conceived
  • acid leaches
  • reasonable agreement
  • sedimentation rates

  • age estimated
  • inseparable contamination
  • radium standard
  • ages obtained
  • recently formed

  • method originally
  • method depends
  • formed marine
  • radioactive equilibrium
  • precise independent

  • previous interglacial
  • probably due
  • standard samples
  • shell samples
  • ates sufficiently

  • samples indicates
  • ocean cores
  • spitsbergen shells
  • interglacial period
  • contemporary shells


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