Characterisation and palaeoclimate of a loess-like permafrost palaeosol sequence in NE Siberia

Abstract

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 (C org > 1%) characterise the dark grey glacial palaeosols, whereas lower contents (C org ≤ 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.