U-Th Chronology: Sample Selection and Sample Size Recommendations

The following recommendations are general guidelines which help us to provide better service to our customers. Individual sample size requirements primarily vary based on the sample type. We always recommend that you choose the best samples for your research objectives. Please feel free to contact us for advice if you are concerned that your samples are too small.

Coral – 30 to 50 mg: For the best results, make sure your samples are clean and free from clay particles and other detritus. It is highly recommended to check the mineralogy of your sample. Choose samples with the highest amount of aragonite. Homogenize your samples, preferably using an agate mortar and pestle, and transfer into plastic or glass vials. Homogenized samples are digested in 6 M nitric acid (lower concentrations may be used if the sample contains clay and detritus).

Stalagmite and Flowstone – 100 to 150 mg: Homogenize your samples, preferably using an agate mortar and pestle, and transfer into plastic or glass vials. Homogenized samples are digested in 6 M nitric acid.

NOTES:

  • All samples will be screened for U and excess Th prior to isotope dilution and extraction chromatography processes for purification and measurement. Only samples with acceptable ranges of Th will be selected for analysis. If a sample is considered not suitable for analysis, the client will only be charged for the screening.
  • Samples that did not remain closed with respect to U and Th isotopes will yield ages that may not fit in with established chronologies.
  • We utilize an analytical method which provides precise measurement of 233U-234U-235U-236U-238U-229Th-230Th-232Th with high resolution whether a sample remained closed with respect to U and Th or displays open system behavior.
  • Do not leach samples for cleaning, even with weak acid, as leaching has been shown to significantly affect the uranium concentration in the sample, leading to erroneous ages.

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