Eurasian Loess Research Articles

North Atlantic abrupt climatic events of the last glacial period recorded in Ukrainian loess deposits

Abstract. Loess deposits are widely distributed in the Northern Hemisphere, where they have recorded not only the glacial-interglacial cycles, but also millennial-timescale changes resembling those in marine and ice cores. Such abrupt variations are clearly marked in western European series, but have not yet been evidenced in the East of the continent. Here we present results of the high-resolution investigation of a Weichselian Upper Pleniglacial loess sequence (~38–15 ka) from Stayky, Ukraine. The stratigraphy shows an alternation of loess horizons and embryonic soils, similar to sequences from western Europe. Similarities are also found between variations of a grain-size index (ratio between coarse and fine material fractions) in Stayky and in western European profiles. Based on these similarities and in agreement with the luminescence dates, the embryonic soils are associated with the Greenland interstadials (GIS) 7 to 2, and the Vytachiv paleosol at the base of the sequence, with GIS 8. Pollen analysis indicates a wetter climate for these interstadials, allowing the development of arboreal vegetation, than for the stadials, which are marked by loess formation. The grain-size index reaches the highest values for intervals correlated with the Heinrich events 3 and 2. Thus, it appears that the North Atlantic abrupt climate changes have extended their influence and modulated the loess sedimentation at least as far as eastern Europe. This result is supported by recent climate modeling experiments and recommends the Stayky sequence as a reference for further comparisons between profiles along the Eurasian loess belt centered at 50° N.

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

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.

Middle and Late Pleistocene loess sequences at Batajnica, Vojvodina, Serbia

Loess sequences in the Vojvodina region (Northern Serbia) reveal a continuous record of paleoclimatic variations during the Middle and Late Pleistocene. The most detailed stratigraphic information comes from remarkable exposures on the cliffs of the right Danube bank from Vukovar to Belgrade. The Batajnica loess section has been recognized as one of the most complete Middle and Late Pleistocene records in this region. A more than 40 m thick loess–paleosol succession represents environmental transition from relative thin loess layers and rubified soils in lower part of profile to thick loess and fossil chernozems characterizing the last three glacial–interglacial cycles. The proposed stratigraphic model is based on a detailed magnetic susceptibility (MS) record which is related to the deep-sea isotope stratigraphy and on correlation with other Eurasian loess records using the distinct MS pattern of selected loess–paleosol couplets. This new stratigraphic model suggests serious revision of previous chronological interpretations. MS as function of depth shows a well-known pattern of low values in loess and high values in paleosols indicating strong enhancement of magnetic minerals during soil formation. With the exception of the recent soil (V-S0) which is strongly contaminated by archaeological artifacts, the third paleosol V-S3 reveals the highest values in MS and a very distinct double peak. The rock magnetic signal at Batajnica resembles the typical pattern of the enviromagnetic records determined from other Eurasian loess sites. The paleopedological interpretations, rubification index values and rock magnetic record at Batajnica yield valuable data for the reconstruction of paleoclimatic fluctuations for the last 5 glacial–interglacial cycles at least. Moreover, the record provides an important link between the classical Central European loess sites and the Central Asian and Chinese loess provinces.

Misleading positions of geomagnetic reversal boundaries in Eurasian loess and implications for correlation between continental and marine sedimentary sequences

The Matuyama–Brunhes boundary (MBB) where the Earth's magnetic field changed to its present orientation is one of the most frequently used time markers in continental Quaternary stratigraphy. Although magnetic signals have been successfully recovered from loess deposits and an apparently coherent magnetostratigraphy seems to be in place, a close examination of the published loess records from northern mid-latitudes reveals significant uncertainty and variability for the position of the MBB. In Asia and part of Central Europe, the MBB has been found in loess, a glacial deposit. This is in contrast to the well-established palaeomagnetic records in deep-sea sediments where the MBB is located in the interglacial Oxygen Isotope Stage 19. This discrepancy has caused serious confusion in stratigraphic correlation between loess and marine sequences. Here we examine the causes of the discrepancy between the two sedimentary environments in their records of the MBB. Our approach includes a comparison of the MBB in loess and other continental records, and an evaluation of the stratigraphic significance of the microtektites found around the MBB. Based on the occurrence of the MBB in an interglacial stage in lake and continental margin sequences and the correlative stratigraphic positions of the microtektites in marine sediments and loess, we demonstrate that the measured positions of the MBB in loess are erroneous and misleading, and its true occurrence was during the time of formation of the palaeosol corresponding to Oxygen Isotope Stage 19. The most plausible cause for the apparent offset, i.e. the MBB being found in the underlying loess instead, is that the acquisition of remanent magnetisation in loess occurs at a certain depth substantially below the land surface. The degree of such displacement is dependent on the lithology and structure of the deposits formed prior to the reversal, and the time delay is estimated to be in the order of 103–104 years. We show that other geomagnetic boundaries, such as those of Jaramillo and Cobb Mountain, in loess have been similarly displaced though to a varying extent. We suggest that the remanence acquisition in loess is closely related to the post-depositional evolution in the structure of loessic materials which is in part influenced by regional climate conditions. Our conclusions on the displaced remanence acquisition have implications for loess chronology, magnetostratigraphy as well as the geomagnetic interpretation of detailed magnetic signatures from loess.

Late Pleistocene Climatic Variations at Achenheim, France, Based on a Magnetic Susceptibility and TL Chronology of Loess

New field investigations of the Achenheim sequence (Alsace, France) allow for the characterization of variations in the low-field magnetic susceptibility over most of the last climatic cycle, i.e., the past 130,000 yr. New stratigraphic data and thermoluminescence measurements permit reassessment of the previous chronological interpretation of the Upper Pleistocene at Achenheim. A high-resolution analysis of magnetic susceptibility discloses the occurrence of a fine-grained “marker” horizon which was also found recently in another section. This horizon is interpreted as a small-scale dust layer deposited prior to the main interval of loess deposition. The horizon, deposited at the marine isotope stage (MIS) 5/4 boundary, has been found in other loess sequences and is especially prevalent in central Europe. It is characterized by low susceptibility values and a grayish color. New thermoluminescence dates indicate that the loess deposition took place after the MIS 5/4 boundary, i.e., after 70,000 yr. These results are consistent with the Greenland GRIP ice-core dust record which also demonstrates a dusty atmosphere after 72,000 yr ago. On a more regional scale, the Achenheim loess sequence demonstrates a reliable correlation between the western side of the Eurasian loess belt and the dust record of the Greenland ice cores.