A high-resolution Late Quaternary climatostratigraphic record from Iskitim, Priobie Loess Plateau, SW Siberia

摘要

The Siberian loess, being a part of the Eurasian loess belt, has provided the most complete terrestrial record of past climate change in the north-central Asia. The continuous high-resolution sections of aeolian dust deposits inter-bedded with fossil soils from the Priobie Loess Plateau and the Northern Altai Plains - mapped as a part of the 2000 km W-E Siberian palaeoclimate transect - have produced extraordinary evidence of the Late Quaternary climate evolution and landscape development in the parkland-steppe north of the Altai-Sayan Mountains. A complete stratigraphic loess-palaeosol record was studied at the Iskitim reference section, spanning the last c. 250 ka (MIS 7-1). The climate-indicative proxy data (magnetic susceptibility, grain size, %CaCO_3, %TOC) and thin-section studies show marked and cyclic climatic variations, particularly pronounced during the Last Interglacial-Glacial cycle equivalent to the loess reference sites from the Yenisei and Katun/Altai Plain areas (the Kurtak and Krasnogorskoye sections). The Iskitim loess-palaeosol record illustrates a rapid onset of the Last Interglacial in agreement with the marine oxygen isotope records, with a strongly continental warm climate culminating around the peak of the Last Interglacial (MIS 5e). This was succeeded by a dramatic cooling (MIS 5d) defined by a major cryogenic event that resulted in deformation of the MIS 5e chernozem followed by loess deposition in congruence with the Lake Baikal detrital stratigraphic sequence. Cooler climate conditions during the subsequent interglacial sub-stages (MIS 5c and 5a) correspond to shifts in the bioclimatic zonal development, with a gradual replacement of parkland-steppe and mixed southern taiga by boreal forest, and by cold arid periglacial tundra-steppe during the stadial sub-stages (MIS 5d and 5b). Following the most intensive loess sedimentation during the early Last Glacial (MIS 4), a new cycle with warm and very cold climate variations characterises the mid-Last Glacial interstadial interval (MIS 3), with most favourable surface-stabilisation phases represented by cryogenically distorted parkland chernozem soils. The Iskitim loess-palaeosol sequence, characterised by intensive syndepositional pedogenic processes, provides unique evidence of a dynamic climate change during the Late Quaternary in the continental north-central Asia and a linkage site for transcontinental Eurasian correlations of high-resolution loess records.