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Such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data.
Future comminution studies would benefit from further consideration of the importance of 1) leaching lost 234U from source rock and bulk sediment samples, 2) wind deposition of fine-grained material and 3) the appropriateness and robustness of sample pre-treatment procedures.
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U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years.
Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals.
This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed.
Significant input of aeolian material may modify the measured (234U/238U) activity ratios.
Typically closed systems with high 234/238 ratios and little initial Th-230, these samples have yielded some of the most precise and accurate ages of the climate system over the last half million years.U at the time of sample formation must be known or calculated. With time, Thorium 230 accumulates in the sample through radiometric decay. The largest radioactive disequilibria are always found in the youngest materials.Over time, this signature goes away, eventually relaxing to a condition wherein the disequilibria are no longer detectable.
For instance, when crystals form in a magma, Th, U and Ra in the magma enter the different materials in different proportions, producing radioactive disequilibrium.