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Geoscientists from the Universities of Cologne and Göttingen develop a novel geochemical approach to analyse landscape evolution: cosmogenic krypton, a rare noble gas, provides information on how long sediments remained on the Earth’s surface / publication in PNAS
An international research team involving the University of Cologne has found a new way to reconstruct how landscapes developed tens of millions of years ago and how long sediments remained on the Earth’s surface before they were deposited. The investigation of cosmogenic krypton in zircon minerals makes it possible for the first time to quantitatively record the transport and retention times of sediments over millions of years. Cosmogenic krypton is a rare noble gas that is produced when cosmic radiation hits minerals on the Earth’s surface. Analysing these minerals can therefore show how long they were on the Earth’s surface. The study titled “Ancient landscape evolution tracked through cosmogenic krypton in detrital zircon” was published Proceedings of the National Academy of Sciences (PNAS). The researchers show that cosmogenic krypton in certain tiny mineral grains can be used to quantitatively reconstruct landscape development around 40 million years ago.
The study is based on sediment samples from several drill cores in the Eucla Basin in southern Australia, one of the world’s most important zircon deposits. The researchers combined measurements of stable cosmogenic krypton isotopes with the established U-Pb dating of zircons. U-Pb dating is a method that allows researchers to determine when these minerals were formed millions or even billions of years ago based on the natural decay of uranium to lead in resistant minerals such as zircon. While the U-Pb ages mainly provide information about the origin of the mineral grains, the cosmogenic krypton allows conclusions to be drawn about how long these minerals were exposed to cosmic radiation at or near the Earth’s surface – a direct measure of transport, storage, and erosion processes.
The results show that some of the zircons remained on the Earth’s surface for more than a million years before they were finally deposited. Particularly striking is a phase of change from long-stored, heavily ‘weathered’ sediments from the time of high global temperatures in the middle Eocene to more dynamic transport with shorter residence times thereafter. This change coincides with fluctuations in sea level and tectonic processes and reflects a fundamental change in the dynamics of the landscape. The study thus reveals how closely climate, tectonics, and sediment transport are linked over geological time periods.
“The method developed in Cologne for cosmogenic krypton in zircons allows us for the first time to quantitatively record the surface history of zircon-containing sediments in very old geological systems,” says Professor Dr Tibor J. Dunai from the University of Cologne’s Institute of Geology and Mineralogy. “Until now, such studies were limited in by the relatively short half-lives, on geological time-scales, of other commonly used cosmogenic nuclides.”
In the long term, the method opens up new perspectives for studying old, tectonically stable continents whose landscape histories were previously difficult to quantify. The researchers expect that cosmogenic krypton can also be used in other regions in the future to better understand the influence of climate and environmental changes on the Earth’s surface over millions of years.
Press and Communications Team:
Jan Voelkel
+49 221 470 2356
j.voelkel@verw.uni-koeln.de
Press Spokesperson: Dr Elisabeth Hoffmann – e.hoffmann@verw.uni-koeln.de
Media Contact:
Professor Dr Tibor Dunai
Institute of Geology and Mineralogy
+49 221 470 3229
t.dunai@uni.koeln.de
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