EGU2020-13827
https://doi.org/10.5194/egusphere-egu2020-13827
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The potential of ingrowth 226-Ra as a new dating tool for late Holocene carbonate deposits

Marie-Louise Froeschmann1, Denis Scholz1, Hubert Vonhof2, Klaus Peter Jochum2, Cees W. Passchier1, and Gül Sürmelihindi1
Marie-Louise Froeschmann et al.
  • 1Johannes Gutenberg University Mainz, Institute of Geosciences, Speleothem Research, Germany (mfroesch@students.uni-mainz.de)
  • 2Max Planck Institute for Chemistry, Mainz, Germany

One of the most commonly used methods for dating carbonate deposits, such as speleothems or calcareous sinter deposits, is the 230Th/U-disequilibrium method. With this approach, ages up to 500 ka can be obtained. However, especially for late Holocene samples, substantial detrital contamination may represent a major problem for radiometric dating. The high 232Th content, which is an indicator for the amount of detrital contamination, leads to elevated U/Th-ages and generally larger uncertainties, which limit the potential of the corresponding samples for paleoclimate reconstructions. Ingrowth 226Ra shows the potential to be used as an alternative dating method. In combination with Ba, U and Th, it is possible to date samples with ages up to 8 ka.

In general, there are three sources of 226Ra in carbonate samples. (i) excess 226Ra incorporated during deposition of the material, (ii) detrital material present in the carbonate, and (iii) ingrowth 226Ra produced by the radioactive decay of its parent 230Th. Due to the geochemically similar behavior of Ra and Ba, it is possible to correct for the amount of excess 226Ra. As for the 230Th/U-disequilibrium method, 232Th can be used to correct for detrital contamination.

To test our new method, we applied it to several calcareous sinter samples from different Roman aqueducts, which supplied drinking water to ancient cities such as Jerash or Cordoba . The separation of Ra, Ba, U and Th from the matrix of the samples is performed using a single aliquot of material and different ion exchange resins. Prior to the separation process, a calibrated mixed Ra-Ba-Th-U spike solution was added and equilibrated with the sample solution. The results are not only compared to model simulations for the new system, but also to ages obtained with the conventional 230Th/U-method.

How to cite: Froeschmann, M.-L., Scholz, D., Vonhof, H., Jochum, K. P., Passchier, C. W., and Sürmelihindi, G.: The potential of ingrowth 226-Ra as a new dating tool for late Holocene carbonate deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13827, https://doi.org/10.5194/egusphere-egu2020-13827, 2020.

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