Reconstruction of Late-Glacial lake-level fluctuations in The Netherlands based on palaeobotanical analyses, geochemical results and pollen-density data |
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| Authors: | SJOERD BOHNCKE LEX WIJMSTRA |
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| Institution: | Free University, Institute of Earth Sciences, P. O. Box 7161, 1007 MC Amsterdam, The Netherlands;University of Amsterdam, Hugo de Vries Laboratorium, Section Palynology and Palae/Actuoecology, Kruislaan 318, 1098 SM Amsterdam, The Netherlands |
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| Abstract: | The Late-Glacial infills of three lake successions in The Netherlands have been analysed for their palaeobotanical content (pollen, macroremains) as well as for their physical and chemical characteristics. The macro-botanical analysis in association with the pollen analysis permitted the reconstruction of relative lake level fluctuations for each lake. There appeared to be good agreement between the three lake successions. Supporting evidence for the presence of alternating dry and wet phases was found in the geochemical results. The termination of the Bölling biozone coincides with a lowering of the lake levels that persisted throughout the Older Dryas. Water levels restore at the beginning of the Allerod biozone. Several fluctuations are recognized during the Allerod. The end of the Alleröd is characterized by a second major lowering in the lake levels, leading to an interruption in the sedimentation in cores from the fringe zone. Water depth increases at the beginning of the Younger Dryas biozone. A third major minimum in the lake levels is reached towards the end of the Younger Dryas biozone, probably explaining the recurrent hiatus at the transition to the Holocene record. Pollen concentration data in association with chronostratigraphical data provided the construction of sedimentation rate curves. Minima in these sedimentation rate curves appeared to correlate with periods of low lake level. The loss on ignition curve in association with the sedimentation rate data allowed an approximation of the organic production of the lakes involved. It revealed that the darker appearance of the Allerödin the lithologycan be ascribed mainly to a retardationin the sedimentation rate and not to a major increase in the organic production of the lakes. |
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