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Rebecca Keulertz, Start-up Honours Grant, 2015-2016

The geomorphological application of cosmogenic nuclides from iron oxides

Vogelsberg (Germany) ‐ sampling of river sediments together with Tomasz Goral (Institute of Geology and Mineralogy) and students 09/2015 (© Rebecca Keulertz)

In advance I want to thank the GSGS and the steering committee for funding my start-up honour grant, which I received from 06/2015 to 02/2016.
During the last months I accomplished preparatory work for my PhD project and the corresponding DFG proposal. In my PhD thesis I want to apply the cosmogenic isotope dating technique to iron oxides. One of the cosmogenic radionuclides that can be used for Earth-science application is 53Mn. In situ 53Mn is produced by cosmic rays (mainly spallation reactions) on Fe, thus 53Mn is valuable in landscapes were Fe-bearing minerals remain after other (less resistant) minerals have been weathered away. This fact, together with the long half- life time of 53Mn at 3.7 Ma, means it can be used for examining erosion-rates at the timescale of the order of 1 Ma.
The last months I used for literature research to prepare for my PhD thesis. I achieved an overview of the state of the art of this recent addition to the terrestrial cosmogenic toolbox.
I assisted Dr. Binnie with the preparation of a DFG proposal. For the geomorphological application of in situ 53Mn in iron oxides it was necessary to find a suitable study area. As I am going to focus on erosion studies a region where iron-bearing rocks are ubiquitous and erosion rates are unknown over large time-scales might be applicable. Continental flood basalt provinces (CFB) are well suited for the implementation of cosmogenic 53Mn. They are relatively rare occurrences at the Earth`s surface (they cover nearly 3% of the continental surface). Much of their original volume may have disappeared since emplacement because of various forms of erosion. The present remaining volumes of CFB often underestimate the original volumes (Courtillot&Renne2003; Dessert et al. 2001). Dessert et al. (2001) outlines the importance of early erosion of the traps linked to increased atmospheric CO2 content. Long-term erosion rates are still missing for those areas or associated with very large uncertainties. The cosmogenic nuclide dating technique using 53Mn in iron oxides, for example in magnetites separated from basalts, would be a great improvement to unravel the erosion histories of CFB.
During the last months I sampled river sediments from stream placer of small rivers draining the Vogelsberg, a basalt region in Germany. For a small pilot study I developed a magnetic retrieval technique to quantitatively separate magnetites from river sediments.
Further more I did some experiments, where I tried to selective dissolve magnetites using the acid-ammonium oxalate/ferrous iron extraction method. This might be useful in cases where you want to measure multiple cosmogenic isotopes within the same iron oxide. Especially for cosmogenic 36Cl this might be an alternative to HCl that is commonly used for dissolution. The selective dissolution of magnetites is also useful when you want to improve mineral specific production rates of cosmogenic nuclides.
Together with Björn Dittmann (PhD candidate Institute of Geology and Mineralogy, UoC), who is working on the chemical preparation of Accelerator Mass Spectrometry (AMS) targets, I processed terrestrial iron oxide samples from Chile. In this way I was able to learn all chemical separation steps that are required to produce high-quality targets for subsequent AMS measurements.
Furthermore, I participated in several activities offered by the Graduate School of Geosciences, for example the Geoscience Colloquiums and the GSGS Research Conference 2016. In the poster session of this Conference I presented a voluntary poster showing the research results of my Master Thesis.

I would like to thank the GSGS and the steering committee for funding my research and enabling me a smooth transition between my graduation and my ongoing PhD studies.

References:

Courtillot, V.E. & Renne, P.R., On the ages of flood basalt events, 2003. In: Comptes Rendu Geoscience, (335) 113-140.

Dessert, C.; Dupré, B.; Francois, L.M.; Schott, J.; Gaillardet, J.; Chakrapani, G.; Bajpai, S.; 2001: Erosion of Deccan Traps determined by river geochemistry: impact on the global climate and the 87Sr/86Sr ratio of seawater. Earth and Planetary Science Letters, (188) 459-474.



Start-up Honours Grant
1 June 2015 to 29 February 2016
Cologne, Germany

Rebecca Keulertz
MSc.

PhD project: “The geomorphological application of cosmogenic nuclides from iron oxides”

Institute of Geology and Mineralogy

Thesis: The geomorphological application of cosmogenic nuclides from iron oxides

Supervisor: Prof. Dr. Tibor Dunai