Articles | Volume 12, issue 24
https://doi.org/10.5194/bg-12-7453-2015
https://doi.org/10.5194/bg-12-7453-2015
Research article
 | 
17 Dec 2015
Research article |  | 17 Dec 2015

Age–depth model of the past 630 kyr for Lake Ohrid (FYROM/Albania) based on cyclostratigraphic analysis of downhole gamma ray data

H. Baumgarten, T. Wonik, D. C. Tanner, A. Francke, B. Wagner, G. Zanchetta, R. Sulpizio, B. Giaccio, and S. Nomade

Abstract. Gamma ray (GR) fluctuations and potassium (K) values from downhole logging data obtained in the sediments of Lake Ohrid from 0 to 240 m below lake floor (b.l.f). correlate with fluctuations in δ18O values from the global benthic isotope stack LR04 (Lisiecki and Raymo, 2005). GR and K values are considered a reliable proxy to depict glacial–interglacial cycles, with high clastic input during cold and/or drier periods and high carbonate precipitation during warm and/or humid periods at Lake Ohrid. Spectral analysis was applied to investigate the climate signal and evolution over the length of the borehole. Linking downhole logging data with orbital cycles was used to estimate sedimentation rates and the effect of compaction was compensated for. Sedimentation rates increase on average by 14 % after decompaction of the sediment layers and the mean sedimentation rates shift from 45 cm kyr−1 between 0 and 110 m to 30 cm kyr−1 from 110 to 240 m b.l.f. Tuning of minima and maxima of gamma ray and potassium values versus LR04 extrema, in combination with eight independent tephrostratigraphical tie points, allows establishing of a robust age model for the downhole logging data over the past 630 kyr.

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Short summary
Gamma ray (GR) fluctuations and K values from downhole logging data obtained in the sediments of Lake Ohrid correlate with the global climate reference record (LR04 stack from δ18O) (Lisiecki and Raymo, 2005). GR and K values are considered a reliable proxy to depict glacial-interglacial cycles and document warm, humid and cold, drier periods. A robust age model for the downhole logging data over the past 630kyr was established and will play a crucial role for other working groups.
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