Multiple dating of varved sediments from Lake Łazduny, northern Poland: Toward an improved chronology for the last 150 years

Authors:

• Wojciech Tylmann,
• Dirk Enters,
• Małgorzata Kinder,
• Piotr Moska,
• Christian Ohlendorf,
• Grzegorz Poreba,
• Bernd Zolitschka

Abstract

On two short sediment cores from Lake Łazduny (northeastern Poland) different methods for age estimation were applied including varve counting, ²¹⁰Pb, ¹³⁷Cs and OSL dating. The investigated sediment consists of finely laminated, organic-rich calcareous gyttja interrupted by a sand layer. For ²¹⁰Pb we tested the CFCS, CIC, CRS and SIT models and compared the results with the established varve chronology and the ¹³⁷Cs distribution. The total ²¹⁰Pb activity distribution is consistent between cores and shows a regular decrease with depth. However, the total inventory of unsupported ²¹⁰Pb was significantly different and indicates varying rates of sediment focusing. Our results show that all ²¹⁰Pb dating models used in this study produced different results, while the SIT model performed best in comparison with varve counts and ¹³⁷Cs peaks. The CFCS model produced a realistic age-depth trend but obtained ages were too old compared to the varve time scale. The age estimates provided by the CRS model were too old as well with an increasing offset downcore and the CIC model failed completely by producing an unrealistic chronology with age inversions. This confirms that only systematic testing of different ²¹⁰Pb dating models and routine validation using independent time markers produces reliable ²¹⁰Pb chronologies. OSL dating of two samples from the sand layer provided much too old results which indicate incomplete bleaching during deposition of the analyzed quartz grains. This multiple dating approach demonstrates the considerable potential but also potential pitfalls of dating such young sediments. © 2012 Elsevier B.V.