Rekonstruktion der miozänen Klimaentwicklung in Zentralasien anhand lakustriner Abfolgen in SE-Kasachstan
Zusammenfassung der Projektergebnisse
The quasi-continuous, terrestrial Miocene succession of the Aktau Hills has been identified as a sensitive recorder of orbitally-forced changes in atmospheric moisture supply as well as the regional effects of potential evapotranspiration (PET). Tectonic forcing, instead, played a subsidiary role in the studied time window because of the younger age of the main uplift of the Tian Shan. Age constraints are deduced from an integrated approach of magnetostratigraphy, cyclostratigraphy and U-Pb dating of carbonates. The resulting orbital age model places the studied Aktau succession into the period between 15.5–11.0 Ma. Initiation of lacustrine conditions in the Ili Basin corresponds to the onset of the Miocene Climate Transition (MCT) and is the terrestrial expression of this global climatic event in Central Asia. This answers our first research question, and relates the saline playa lake phase to the MCT instead, as assumed, the Miocene Climatic Optimum. Characterization of the water budget and the evaporation rate is based on semi-quantitative facies records of water level and salinity, as well as records of stable isotopes (δ13C, δ18O), element geochemistry and palynology. A period of extreme aridity and pronounced evaporitic sedimentation between 13.8–13.5 Ma is identified to occur during the MCT, and to be the terrestrial expression of the Badenian Salinity Crisis in Central Asia. It is followed by climate cooling, wetting and lake expansion. Transitions between the different stages occurred within short periods evident from the formation of marker horizons. Their timing is related to lowfrequency modulations of obliquity and eccentricity. Further, they correspond to sea-level and ocean circulation changes within the Central and Eastern Paratethys. Nodes and anti-nodes of obliquity influence the high-to-low-latitudinal insolation gradient and thus the strengths of atmospheric pressure cells. Low pressure gradients prevailed in times of obliquity nodes, which weakened the Westerlies and limited the moisture supply. Further, maxima in eccentricity strongly effect the magnitude of summer insolation and thus of PET. Accordingly, we assume changes in the evolution and pathways of atmospheric pressure cells to have played a crucial role in the distribution of moisture and heat across Central Asia. This emphasizes the contribution of continent-wide atmospheric forcing at the expense of a solely forcing by sea level and tectonics. The marginal seas of the Central and Eastern Paratethys served as a source for atmospheric moisture, which answers our second and third research question. The results of the project raise a series of new questions with potential for future research. Here, we could show that sedimentation was influenced by low-frequency modulations of obliquity and eccentricity. However, the detailed phase relationships between orbital configurations and the non-linearity of the sedimentary response on precessional scale is not well understood yet. Another aspect points to the development of terrestrial climate proxies under arid conditions. Here, we observed different authigenic mineral formations of clays and evaporites, for which the boundary conditions are not well constrained. Their definition in saline lakes will have a future potential to discriminate between evaporation and precipitation-sensitive proxies. Last but not least, high-resolution climate modeling at different orbital extremes with Miocene boundary conditions would be extremely helpful to verifiy the here developed proxy records and to identify atmospheric moisture paths and effects of saisonality.
Projektbezogene Publikationen (Auswahl)
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(2015) Paleomagnetic studies at Aktau Hills, Kazakhstan – preliminary results. DGG Hannover, abstracts
Verestek V, Appel E, Voigt S
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(2016) Climate changes on from Milankovitch orbital to tectonic time scales: Facies development and astronomical forcing in the Miocene terrestrial lacustrine succession of the Aktau Hills in SE Kazakhstan. 32th International Meeting of Sedimentology, Marrakesh, abstract volume
Frisch K, Voigt S
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(2016) Complex magnetic behavior and cyclostratigraphy: reconciling magnetostratigraphic ambiguity in a paleoclimate archive in Central Asia. AGU Fall Meeting Abstracts, GP43B-1241
Verestek V, Appel E, Frisch K, Voigt S
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(2016) Towards an understanding of Central Asia climate evolution during the Miocene - a rock magnetic study in SE Kazakhstan. Castle Meeting, Dinant, abstract volume
Verestek V, Appel E, Voigt S, Frisch K
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(2017) Climatically forced moisture supply, sediment flux and pedogenesis in Miocene mudflat deposits of SE Kazakhstan, Central Asia. Depositional Record 3, 209–232
Voigt S, Weber Y, Frisch K, Bartenstein A, Hellwig A, Petschick R, Bahr A, Pross J, Koutsodendris A, Voigt T, Verestek V, Appel E
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(2017) Long-period astronomical forcing on westerly-driven moisture transport to Central Asia during the Middle Miocene Climate Transition. 33rd International Meeting of Sedimentology, Toulouse, abstract volume p. 934
Voigt S, Frisch K, Hellwig A, Raddatz J, Gerdes A, Voigt T, Verestek V, Appel E
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(2017) Obliquity forcing on moisture supply and eccentricity control on water budget: A Central Asian perspective on the Miocene Climate Transition. 33rd International Meeting of Sedimentology, Toulouse, abstract volume p. 322
Frisch K, Voigt S, Verestek V, Appel A, Voigt T, Hellwig A
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(2017) Tracking water level and evaporation on basin-scale: A detailed facies model for the lacustrine Miocene deposits of the Ili Basin, SE Kazakhstan. 33rd International Meeting of Sedimentology, Toulouse, abstract volume p. 323
Frisch K, Voigt K, Verestek V, Appel E, Voigt T, Hellwig A
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(2018) Constrained Magnetostratigraphic Dating of a Continental Middle Miocene Section in the Arid Central Asia. Frontiers in Earth Science 6, 49
Verestek V, Appel E, Voigt S, Frisch K
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(2018) Late Oligocene–early Miocene humidity change in Central Asia recorded in terrestrial sequences from the Ili Basin (SE Kazakhstan). Sedimentology 65, 517–539
Hellwig A, Voigt S, Mulch A, Frisch K, Bartenstein A, Pross J, Gerdes A, Voigt T
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(2018) Long-period astronomical forcing on Miocene westerly-driven moisture transport to Central Asia. Geophysical Research Abstracts 20, EGU2018-9507
Voigt S, Frisch K, Hellwig A, Raddatz J, Gerdes A, Voigt A, Verestek V, Appel E
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(2018) Relationship between sediment facies and stable isotopes within a lacustrine sequence of mid-Miocene age in SE Kazakhstan. GeoBonn, Abstract volume
Arndt I, Frisch K, Voigt, S
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(2019) Extreme aridity in Central Asia deciphered from terrestrial facies evolution and basin hydrology in the Middle Miocene Ili Basin, SE Kazakhstan. Sedimentology 66, 1716–1745
Frisch K, Voigt S, Voigt T, Hellwig A, Verestek V, Weber Y
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(2019) Rock magnetic signature of a playa cycle in Central Asia and environmental implications. International Journal of Earth Sciences
Verestek V, Appel E, Frisch K, Voigt S
