LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Multiproxy-Analytical Characterisation of a Permafrost Palaeosol Sequence in NE-Siberia
Zech, M.1,2, Zech, R.3, Hambach, U.1, Frechen, M.4, Andreev, A.5, Zech, W.6
1Chair of Geomorphology, University of Bayreuth, Universitätsstr. 30, D-95440 Bayreuth, Germany
2Department of Soil Physics, University of Bayreuth, Universitätsstr. 30, D-95440 Bayreuth, Germany
3Geographical Institute, University of Bern, , CH-3012 Bern, Switzerland
4Leibniz Institute for Applied Geosciences, Geochronology and Isotope Hydrology, 30655 Hannover, Germany
5Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, D-14473 Potsdam, Germany
6Institute of Soil Science and Soil Geography, University of Bayreuth, Universitätsstr. 30, D-95440 Bayreuth, Germany
We studied a 15 m high loess-like permafrost palaeosol sequence (the Tumara Palaeosol Sequence, TPS), which developed on a Middle Pleistocene fluvio-glacial terrace of the Tumara River. Various analytical methods were applied to characterise the TPS.
Similar to typical loess–palaeosol sequences (e.g. in China, Europe etc.), pedogenetic clay formation, mineral weathering and smaller grain sizes are interpreted as representing warmer and more favourable climatic conditions (interglacials or interstadials). Soil organic matter (SOM), however, reveals an unfamiliar, inverse pattern: High organic carbon contents (Corg > 1%) characterise the dark grey glacial palaeosols, whereas lower contents (Corg ≤ 0.5%) are found in the brown interglacial/-stadial palaeosols. This can be explained with permafrost and water logging having inhibited SOM mineralisation during cold periods. D/L ratios of aspartic acid and lysine proved to be useful proxies for both SOM aging and palaeotemperature with amino acid racemization being enhanced in interglacial/- stadial palaeosols.
On the basis of the geochemical and grain size results, further palaeoclimatically relevant proxies describing the palaoewind-strength (U-ratio), the mineral weathering (Chemical Index of Alteration, Rb/K) and the changing mineral input signal (Ba, Ti/Zr, Ti/Al) were applied to the TPS. In combination with numeric dating results (radiocarbon and luminescence) and in the context of other northern hemispheric records, the simple warm-cold stratigraphy as derived from the palaeoenvironment/-climate proxies suggests that the TPS represents the last ~240,000 years.
Alkane biomarker results were corrected for degradation effects by applying an endmember model and evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian Glaciation and finally the reforestation during the Late Glacial and the Early Holocene.