Terrestrial in situ produced cosmogenic nuclides – a geochronological tool for Quaternary geology and geomorphology
Terrestrial in-situ produced Cosmogenic Nuclides (TCN) are suitable for the determination of the exposure age, burial age and denudation rate of rock surfaces, sediments and landforms. The method is applicable in the time range of 102 to 106 years and at variable lithologies. This time range covers the entire Quaternary and Pliocene hence it has occupied a significant role among the tools of Quaternary geochronology.
Most important radioactive TCN in geological and geomorphological research are 10Be (t1/2: 1.387 Ma), 26Al (t1/2: 708 ka), 36Cl (t1/2: 301 ka) and 14C (t1/2: 5730 a). Two stable noble gas nuclides are also important, the 3He and the 21Ne. Radioactive nuclides reach their secular equilibrium after 3-4 half-lives, which defines the applicability range of the method.
See more about the method in: Gosse and Phillips (2001); Dunai (2010); Granger et al. (2013) and references therein.
Exposure age determination
Exposure age of a rock is the time elapsed since it has been exposed to cosmic irradiation. The measured TCN concentration is representative of the exposure age of the studied landform (1) if the formation of the landform was instantaneous and (2) if no surface denudation or (3) sediment accumulation has occurred since its formation. Glacial landforms, fluvial terraces and lava flows are among the most frequent targets of exposure age determination.
Determination of denudation rates
In case of steady erosion TCN concentration within the rock is approaching a secular equilibrium. The faster is the denudation the lower is the equilibrium level. Accordingly, on a surface of long term steady erosion TCN concentrations are suitable for the determination of the surface denudation rate. The method is suitable for the quantification of surface denudation rates (on uncovered or soil mantled surfaces) and for the determination of average erosion rates of entire drainage basins.
Burial age determination
In contrast with exposure age and denudation rate determinations, burial age dating is based on the radioactive decay of cosmogenic nuclides. Those rocks and sediments are suitable for burial dating which once were exposed to cosmic irradiation, but have been buried since then. The time of burial (shielding from cosmic rays) can be determined using cosmogenic nuclide-pairs with different half-lives. Typical example is the burial dating of sediment trapped in caves using the 26Al/10Be nuclide-pair.
Applications in Hungary
The Danube, the major river of the Pannonian Basin system, is the only river cutting through the NE-SW Transdanubian Range (TR). River terraces show an up-warped pattern approaching the axis of the TR documenting differential uplift rates along the river. Numerical age determination of the terraces is essential for the determination of the incision rate of the Danube and connected uplift rate of the TR. First application of in-situ produced cosmogenic nuclides in the region was the age determination of strath terraces of the Danube using in situ produced cosmogenic 3He (Ruszkiczay-Rüdiger et al., 2005). As a continuation of this work exposure age and denudation rate determination of aggradational terraces of the Danube using cosmogenic 10Be depth profiles revealed that the onset of the incision of the Danube was probably triggered by the mid-Pleistocene climate transition between 1.2 and 0.7 ka (Ruszkiczay-Rüdiger et al., 2016a).
Quaternary sediments and landforms of aeolian origin suggest that the role of wind erosion in the Pannonian Basin was also significant during the Quaternary. Aeolian denudation was studied in the western part of the Pannonian Basin using in situ produced cosmogenic 10Be depth profiles. This study enabled the quantification of local and regional aeolian denudation rates for the last 1.5 Ma (Ruszkiczay-Rüdiger et al., 2011).
In the Retezat Mts (Southern Carpatians, Romania) a revised glaical chronology together with novel 10Be exposure age data revealed that the most extended glaciation occurred during the global LGM, around ~21 ka. After several recessional phases during the Lateglacial, 10Be surface exposure ages of the moraines suggest that the last small glaciers disappeared after ~13.5 ka. No evidence of Younger Dryas and Holocene glaciers could be found in the area (Ruszkiczay-Rüdiger et al., 2016b).
Dunai, T.J. 2010. Cosmogenic Nuclides. Principles, Concepts and Applications in the Earth Surface Sciences. Cambridge Univ Press, New York, p. 187.
Gosse, J.C. and Phillips F.M. 2001. Terrestrial in situ cosmogenic nuclides: theory and application. Quaternary Science Reviews, 20. pp. 1475-1560.
Granger, D.E., Lifton, N.A., Willenbring, J. 2013. A cosmic trip: 25 years of cosmogenic nuclides in geology. GSA Bulletin, 125, 1379-1402.
Ruszkiczay-Rüdiger, Zs. , Dunai, T.J., Bada, G., Fodor, L., Horváth, E. 2005. Middle to late Pleistocene uplift rate of the Hungarian Mountain Range at the Danube Bend (Pannonian Basin) using in situ produced 3He. Tectonophysics, 410. 1-4. pp. 173-187.
Ruszkiczay-Rüdiger, Zs., Braucher, R., Csillag, G., Fodor, L., Dunai, T.J., Bada, G., Bourlés, D., Müller, P. 2011 Dating pleistocene aeolian landforms in Hungary, Central Europe, using in situ produced cosmogenic 10Be. Quaternary Geochronology, 6, pp. 515-529.
Ruszkiczay-Rüdiger, Zs., Braucher, R., Novothny, Á., Csillag, G., Fodor, L., Molnár, G., Madarász, B., & ASTER Team, 2016a. Tectonic and climatic forcing on terrace formation: coupling in situ produced 10Be depth profiles and luminescence approach, Danube River, Hungary, Central Europe. Quaternary Science Reviews 131, 127-147.
Ruszkiczay-Rüdiger, Zs., Kern, Z., Urdea, P., Braucher, R., Madarász, B., Schimmelpfennig, I., ASTER Team 2016b. Revised deglaciation history of the Pietrele- Stânisoara glacial complex, Retezat Mts, Southern Carpathians, Romania. Quaternary International, 415, 216-229. doi:10.1016/j.quaint.2015.10.085
Presentation of the new sample preparation laboratory
Our laboratory is ready to process quartz-containing samples for the AMS measurement of their in-situ cosmogenic 10Be and 26Al concentrations.
10Be is the by far the most commonly measured cosmogenic nuclide. Main reasons for its popularity in geological applications: (1) the abundance of the target mineral, quartz, (2) low natural 9Be concentrations, (3) standardized chemistry, (4) good AMS precision, (5) relatively simple production depth profile.
Cosmogenic 26Al is usually used in pair with 10Be. Besides that 10Be and 26Al can be measured on the same aliquot after a standardized chemistry process, the dominance of the 26Al-10Be nuclide pair in geosciences stems from their different half-lives, and relatively well studied 26Al/10Be production ratio. They can be used for burial dating and to solve complex exposure histories.
Sample treatment for cosmogenic in-situ 10Be and 26Al measurement
The setup of the sample preparation laboratory for in-situ produced cosmogenic 10Be and 27Al measurements started in the autumn of 2013.
During 2014-2015, partial treatment of a sample sets (crushing, sieving, quartz purification and etching) occurred in our lab and the extraction chemistry of the cosmogenic nuclides occurred at the CEREGE LN2C (Aix en Provence, France), the location of the accelerator mass spectrometry (AMS) measurements (Ruszkiczay-Rüdiger et al., 2016b). In 2015-2016 years already the complete chemical processing of test sample sets was possible, and first results and their interpretation are on their way (Ruszkiczay-Rüdiger et al., 2016; 2017a,b; Neuhuber et al., 2016) .
Physical treatment of the samples
From July 2017 crushing of rock samples occurs with a new Fritsch jaw crusher (Pulverisette 1, Model 2, Premium Line). (Earlier crushing occurred by a Retsch BB200 jaw crusher at the Central research and Instrument Centre of the Eötvös University, Budapest).
Sieving occurs using a Retsch AS200 Vibratory Sieve Shaker in the Laboratory for Sediment and Soil Analysis of the Research Centre for Astronomy and Earth Sciences, Geographical Institute.
Chemical treatment of the samples
After getting rid of the carbonate and organic matter content, the samples are subjected to heavy liquid separation (LST fastfloat) if minerals outside quartz (e.g. feldspars, heavy minerals, mica) are abundant.
Then samples are chemically etched in (HCl-H2SiF6) and pure quartz is dissolved in in the presence of 9Be carrier and evaporated. After substitution of HF by nitric- then hydrochloric acids (HNO3 and HCl), ion exchange columns (Dowex 1x8 and 50Wx8) are used to extract 10Be (Merchel and Herpers, 1999). Hydroxides are ignited at 800°C to reach the purified BeO and Al2O3 for the AMS target.
Budaörsi út 45., H-1112, Budapest, Hungary
The laboratory was equipped with the help of the National Scientific Found of Hungary (OTKA PD 83610) and with contributions of the “Lendület” program of the Hungarian Academy of Sciences (LP2012-27/2012).
- 27Al concentrations (in case of samples for 26Al measurements)
are determined at the Department Institute of Applied Chemistry, Eötvös University, Budapest Nuclear Research of the Hungarian Academy of Sciences, Hertelendy Laboratory of Environmental Studies, Debrecen using a ThermoFinigan Element2 ICP-MS an Agilent MP-AE S 4100 facility.
- MS measurements of isotope ratios of purified BeO and Al2O3 samples occurs at ASTER, the French National Facility, CEREGE, Aix en Provence (Arnold et al., 2010) in the framework of scientific cooperation.
- Arnold, M., Merchel, S., Bourlès, D.L., Braucher, R., Benedetti, L., Finkel, R.C., Aumaître, G., Gottdang, A., Klein, M., 2010. The French accelerator mass spectrometry facility ASTER: improved performance and developments. Nuclear Instruments and Methods in Physics Research B 268, 1954–1959.
- Merchel, S., Herpers, U., 1999. An Update on Radiochemical Separation Techniques for the Determination of Long-Lived Radionuclides via Accelerator Mass Spectrometry, Radiochimica Acta 84, 215-219.
Neuhuber, S., Ruszkiczay-Rüdiger, Zs., Decker, K., Braucher, R., Fiebig, M., Braun, M., Molnár, G., Lachner, J., Steier, J., ASTER Team. 2016. Interlaboratory comparison of sample preparation in Vienna and Budapest by isochron burial dating of Danube terraces. Third Nordic Workshop on cosmogenic nuclide techniques, June 8–10, 2016, Stockholm. 42-43.
Ruszkiczay-Rüdiger, Zs., Madarász, B., Kern, Z., Braucher, R., Urdea, P. 2016. Late Pleistocene glacier chronology of the Retezat Mts, Romania, Southern Carpathians. Third Nordic Workshop on cosmogenic nuclide techniques, June 8–10, 2016, Stockholm. 47-48
Ruszkiczay-Rüdiger, Zs., Madarász, B., Kern, Z., Urdea, P., Braucher, R., ASTER Team 2017a. Late Pleistocene deglaciation and paleo-environment in the Retezat Mountains, Southern Carpathians. Geophysical Research Abstracts 18, EGU2017-2755
Ruszkiczay-Rüdiger, Zs., Neuhuber, S., Decker, K., Braucher, R., Fiebig, M., Braun, M., Lachner, J., ASTER Team 2017b. Isochron burial dating of the Haslau terrace of the Danube (Vienna Basin) and interlaboratory comparison of sample preparation in Vienna and Budapest. Geophysical Research Abstracts 18, EGU2017-6239