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| Titel |
Astronomical forcing of Eocene monsoons in terrestrial sediments of the northeastern Tibetan Plateau |
| VerfasserIn |
Niels Meijer, Rik Tjallingii, Mustafa Kaya, Alexis Licht, Hemmo Abels, Yang Zhang, Zhaojie Guo, Zhongping Lai, Guillaume Dupont-Nivet |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151513
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| Publikation (Nr.) |
 EGU/EGU2017-16107.pdf |
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| Zusammenfassung |
| Astronomical forcing of Eocene monsoons in terrestrial sediments of the northeastern Tibetan Plateau
Niels Meijer1*, Rik Tjallingii2, Mustafa Kaya1, Alexis Licht3, Hemmo Abels4, Yang Zhang5, Zhaojie Guo5, Zhongping Lai6, Guillaume Dupont-Nivet1,5,7
1) Institute of Earth and Environmental Sciences, Universität Potsdam, Germany.
2) Section 5.2: Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, Germany.
3) Department of Earth and Space Sciences, University of Washington, USA.
4) Department of Geosciences and Engineering, Delft University of Technology, The Netherlands.
5) Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, Beijing, China.
6) School of Earth Sciences, China University of Geosciences, Wuhan, China.
7) Géosciences Rennes, UMR CNRS 6118, Université de Rennes, France.
*meijer@uni-potsdam.de
Monsoons are the major source of moisture for NE Tibet but their dynamics remain poorly understood. To provide insight into their driving forces we focus on early monsoonal records during the transition from a greenhouse to an icehouse world, as a part of the ERC “MAGIC” project.
The continental mudrocks of the Xining Basin in NE Tibet provide a unique opportunity to study early monsoons because of their relatively continuous deposits from 40 to 15 Ma yielding reliable records of Earth’s magnetic reversals and observed astronomically-forced alternations of monsoonal moisture. This study specifically aims to extend the stratigraphy further back in time to examine cyclicity from the Early Eocene Climate Optimum (EECO) to the MECO.
Magnetostratigraphic analysis of three parallel sections near Xining shows three chrons that are correlated to C20, C21 and C22. The correlation is supported by U/Pb radiometric dating of zircons in a tuff (50.0 ± 1.1 Ma). The lithostratigraphy shows dry mudrocks alternating with wetter fluvio-lacustrine intervals in regular 10-12 meter cycles. These cycles could be paced by the 405 kyr eccentricity cyclicity according to the age model. XRF scanning of the record reveals three main geochemical components reflecting relative variations of carbonate (Ca), gypsum (S) and lithogenics (Ti). Spectral analysis on these components confirm the observed lithostratigraphic cycles and reveals higher frequency cycles in the carbonate/gypsum content of the muds. Towards the Late Eocene the lacustrine intervals become increasingly gypsiferous followed by the onset of obliquity cyclicity at the Middle Eocene Climatic Optimum (MECO) and up to the Eocene-Oligocene Transition (EOT). This suggests a shift in forcing mechanisms on the monsoons during the transition from greenhouse to icehouse conditions in the latest Eocene. |
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