Accretional soil formation in northern hemisphere loess regions - evidence from OSL-dating of the P/H climatic transition from China, Europe and North America

Abstract

[eng] Here we investigate the timing of Pleistocene-Holocene climatic transition as reflected in nine luminescence dated loess-palaeosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, Nebraska, USA. First, logs of high-resolution magnetic susceptibility and its frequency dependence were used as palaeoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil. Second, the onset of increase in their values above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. The variability seen in the magnetic susceptibility records are interpreted based on high-resolution luminescence dating applied on multiple grain-sizes (4-11 µm, 63-90 µm, 90-125 µm) of quartz extracts from the same sample. In order to increase the overall precision of the luminescence based chronology we rely on weighted average ages. Based on these, Bayesian modeling allowed the determination of age-depth models and mean sedimentation rates for each investigated site. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. At all but one site, this increase, associated to the onset of the Pleistocene-Holocene boundary (ie., 11.7 ka) was dated to 14-17.5 ka or even earlier. Our results highlight the need of combining palaeoclimatic proxies (magnetic susceptibility) with absolute dating when placing the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid misinterpretations in loess-paleosol records caused by simple pattern correlation. These results indicate diverse environmental dynamics recorded in the different North Hemisphere loess regions during the major global climatic shift from the last glacial to the Holocene. The detailed luminescence chronology coupled with magnetic susceptibility records indicate the formation of accretional Holocene soils in the sites investigated. Modeled accumulation rates for the Holocene soil are similar for European, Chinese and American loess sites investigated and vary from 0.02 m/ka to 0.09 m/ka.