<abstract xmlns="http://www.w3.org/1999/xhtml"> Varved lake sediments from Lake Zabihskie (northeastern Poland) provide a high- resolution calendar-year chronology which allows validation of 14C dating results. Microscopic analy­sis of the varve microfacies revealed that laminations found in Lake Zabihskie were biogenic (calcite) varves. Three independent counts indicated a good preservation quality of laminae in the 348 cm long sediment profile which contained 1000+12/-24 varves. The varve chronology was validated with the 137Cs activity peaks, the tephra horizon from the Askja eruption at AD 1875 and with the timing of major land-use changes of known age inferred from pollen analysis. 32 AMS 14C dates of terrestrial macrofossils distributed along the profile were compared with the varve chronology. After identifica­tion of outliers, the free-shape model performed with 21 14C dates provided the best possible fit with the varve chronology. We observed almost ideal consistency between both chronologies from the present until AD 1250 while in the lower part (AD 1000-1250) the difference increases to ca. 25 years. We demonstrate that this offset can be explained by too old radiocarbon ages of plant remains trans­ported to the lake by the inflowing creek. Results of this study highlight that careful interpretation of radiocarbon age-depth models is necessary, especially in lakes where no annual laminations are ob­served and no independent method are used for cross-validation.</abstract>

Varved lake sediments from Lake Zabihskie (northeastern Poland) provide a high- resolution calendar-year chronology which allows validation of 14C dating results. Microscopic analy­sis of the varve microfacies revealed that laminations found in Lake Zabihskie were biogenic (calcite) varves. Three independent counts indicated a good preservation quality of laminae in the 348 cm long sediment profile which contained 1000+12/-24 varves. The varve chronology was validated with the 137Cs activity peaks, the tephra horizon from the Askja eruption at AD 1875 and with the timing of major land-use changes of known age inferred from pollen analysis. 32 AMS 14C dates of terrestrial macrofossils distributed along the profile were compared with the varve chronology. After identifica­tion of outliers, the free-shape model performed with 21 14C dates provided the best possible fit with the varve chronology. We observed almost ideal consistency between both chronologies from the present until AD 1250 while in the lower part (AD 1000-1250) the difference increases to ca. 25 years. We demonstrate that this offset can be explained by too old radiocarbon ages of plant remains trans­ported to the lake by the inflowing creek. Results of this study highlight that careful interpretation of radiocarbon age-depth models is necessary, especially in lakes where no annual laminations are ob­served and no independent method are used for cross-validation.

Comparing Varve Counting And 14C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate 14C Dating Of Lake Sediments

Faculty of Oceanography and Geography, University of Gdańsk, Bażyńskiego 4, PL80952 Gdańsk, Poland

Faculty of Physics, Adam Mickiewicz University, Umultowska 85, PL61614 Poznań, Poland

Poznań Radiocarbon Laboratory, Foundation of the Adam Mickiewicz University, Rubież 46, PL61612 Poznań, Poland

W. Szafer Institute of Botany, Polish Academy of Sciences, Lubicz 46, PL31512 Kraków, Poland

Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Erlachstrasse 9a, CH3012 Bern, Switzerland

Geochronometria

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Comparing Varve Counting And C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate C Dating Of Lake Sediments

Varved lake sediments from Lake Zabihskie (northeastern Poland) provide a high- resolution calendar-year chronology which allows validation of 14C dating...

Comparing Varve Counting And ¹⁴C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate ¹⁴C Dating Of Lake Sediments

Publié en ligne: 10 nov. 2015

Pages: -

Reçu: 28 mai 2015

Accepté: 07 sept. 2015

DOI: https://doi.org/10.1515/geochr-2015-0019

Mots clés
lake sediments, varve chronology, AMS 14C dating, radionuclides, age-depth model

© 2015

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Comparing Varve Counting And 14C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate 14C Dating Of Lake Sediments

Publié en ligne: 10 nov. 2015

Pages: -

Reçu: 28 mai 2015

Accepté: 07 sept. 2015

DOI: https://doi.org/10.1515/geochr-2015-0019

Mots cléslake sediments, varve chronology, AMS 14C dating, radionuclides, age-depth model

© 2015

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Comparing Varve Counting And ¹⁴C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate ¹⁴C Dating Of Lake Sediments

Mots clés
lake sediments, varve chronology, AMS 14C dating, radionuclides, age-depth model