Uranium/thorium dating of late pleistocene peat deposits in NW Europe, uranium/thorium isotope systematics and open-system behaviour of peat layers

Abstract

The possibility of dating peat by the uranium-series disequilibrium method is discussed. In principle, this method can be used to date peat to ∼ 350 ka. The application of the U/Th disequilibrium method (UTD) on peat provides us with the probability of constructing a new chronology for the Late Pleistocene paleoclimatic record in NW Europe. The reliability of the obtained ages will be discussed as well as open-system behaviour and the contamination with detrital Th. By studying in detail interglacial peat profiles from the Tenagi Philippon site, Greece (a long terrestrial record), of an expected age of 125 ka and the Fenit site in Ireland of unknown age, we were able to explain the results in terms of the suspected open-system behaviour of top and bottom parts of these layers and how to avoid it by careful sampling. Peals contaminated with detrital Th were also analysed. Two peat layers, which were interpreted on basis of pollen analyses, stratigraphic position and TL dates to be early Last Glacial in age, were sampled. The first one is the Alit Odhar organic layer near Inverness, Scotland, and gave an age of 106 ka. The second is the key site to the British Last Glacial stratigraphy, the Chelford organic layer at Chelford, Cheshire, yielded an age of 86 ka which is in good agreement with the recently obtained TL dates.