| 1. |
- Markovic, Slobodan B., et al.
(författare)
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Danube loess stratigraphy - Towards a pan-European loess stratigraphic model
- 2015
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 148, s. 228-258
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Tidskriftsartikel (refereegranskat)abstract
- The Danube River drainage basin is the second largest river catchment in Europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments. Indeed, the Danube River and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment However, this vast loess province lacks a unified stratigraphic scheme. European loess research started in the late 17th century in the Danube Basin with the work of Count Luigi Ferdinand Marsigli. Since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by Kukla (1970, 1977) in his correlations of loess with deep-sea sediments. Loess-palaeosol sequences in the middle and lower reaches of the Danube River basin were a key part of this framework and contain some of the longest and most complete continental climate records in Europe, covering more than the last million years. However, the very size of the Danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits. Local loess-palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes, which often change significantly with advances in age-dating, have limited the number of basin-wide studies. A unified basin-wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records. Therefore we review the existing stratigraphic schemes and define a new Danube Basin wide loess stratigraphy based around a synthetic type section of the Mosorin and Stari Slankamen sites in Serbia. We present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the Chinese Loess Plateau, with the oxygen isotope records from deep-sea sediments, and with classic European Pleistocene stratigraphic subdivisions. The hierarchy of Danubian stratigraphic units is determined by climatically controlled environmental shifts, in a similar way to the Chinese loess stratigraphic scheme. A new unified Danube loess stratigraphic model has a number of advantages, including preventing confusion resulting from the use of multiple national schemes, a more transparent basis, and the potential to set Pleistocene palaeoenvironmental changes recorded in the Danube catchment area into a global context. The use of a very simple labelling system based on the well-established Chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the Danube Basin loess sites in a wider more accessible context that can be readily correlated world-wide. This stratigraphic approach also provides, for the first time, an appropriate framework for the development of an integrated, pan-European and potentially pan-Eurasian loess stratigraphic scheme.
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| 2. |
- Bradák, Balázs, et al.
(författare)
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Magnetic susceptibility in the European Loess Belt : New and existing models of magnetic enhancement in loess
- 2021
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 569
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic susceptibility measurements play a key role in Quaternary studies. Magnetic proxies, such as low field and frequency-dependent magnetic susceptibility, are widely applied in the reconstruction of terrestrial paleoclimate, e.g., in the study of loess-paleosol successions. In general, the interpretation of loess magnetic susceptibility signals is based on two commonly accepted models: the pedogenic magnetic enhancement and wind-vigour models. However, there are an increasing number of cases where such models cannot be used. These cases show unusual relationships between the two common loess magnetic susceptibility proxies: low field and frequency-dependent magnetic susceptibility. Such relationships have been attributed to various phenomena including the dissolution of fine-grain minerals and the formation of ultrafine magnetic rims on the surface of coarser grains by weathering. Despite the growing number of these exceptional cases of magnetic enhancement, our knowledge about the occurrence and potential causes of the unusual behaviour of magnetic susceptibility parameters is still limited. This, in turn, hinders the wider application of magnetic susceptibility parameters in loess. To fill this knowledge gap, magnetic susceptibility data of various profiles from the European Loess Belt were collected and compared to reveal various enhancement trends in loess. Along with the analysis of magnetic susceptibility parameters, combined scanning electron microscopy (SEM) and rock magnetic analyses were applied to samples from the Paks loess sequence in Hungary to describe some of the irregular cases, notably the cause of increasing frequency-dependent susceptibility in non-altered sediments. Analysis of loess, paleosol and common mineral samples separated from loess (e.g., muscovite) revealed that various features may be responsible for these increasing frequency-dependent susceptibility values: i) surface weathering (maghemitization) of coarser detrital grains, ii) nanofragmentation by physical weathering and iii) the appearance of significant amounts of ultrafine magnetic inclusions in micas. These special modes of magnetic enhancement of loess do not undermine the importance of the basic theories suggested above, but rather provide three mechanisms that account for some of the increasing number of unusual cases. To aid in the wider and more accurate use of magnetic susceptibility parameters in loess, we review the current magnetic enhancement models with special emphasis on the identification of unusual trends in magnetic enhancement and understanding their drivers.
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| 3. |
- Markovic, S.B., et al.
(författare)
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Loess correlations – Between myth and reality
- 2018
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 509, s. 4-23
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Tidskriftsartikel (refereegranskat)abstract
- The correlation of loess sequences across global, hemispheric, regional and local scales is one of the most fundamental aspects to loess research. However, despite recent progress in stratigraphic and chronometric methods, the correlation of many loess sequences is often still based on untested assumptions over loess deposition, preservation, soil type and age. As such, the aim of this overview is to provide an adequate framework for evaluation of the accuracy of loess correlations applied on different temporal and spatial scales across Eurasia. This opens up possibilities for detailed temporal and spatial environmental reconstructions across the huge loess provinces of the Eurasia and provides a framework for future extension of this to North America. Additionally, we evaluate the potential development of appropriate sub-millennial scale loess correlations, as well as essentially important chronological approaches for establishing valid correlations between different loess records, such as current improvements in tephrochronology, C-14 and luminescence dating techniques.
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| 4. |
- Patterson, Nick, et al.
(författare)
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Large-scale migration into Britain during the Middle to Late Bronze Age
- 2022
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; , s. 588-594
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Tidskriftsartikel (refereegranskat)abstract
- Present-day people from England and Wales harbour more ancestry derived from Early European Farmers (EEF) than people of the Early Bronze Age1. To understand this, we generated genome-wide data from 793 individuals, increasing data from the Middle to Late Bronze and Iron Age in Britain by 12-fold, and Western and Central Europe by 3.5-fold. Between 1000 and 875 BC, EEF ancestry increased in southern Britain (England and Wales) but not northern Britain (Scotland) due to incorporation of migrants who arrived at this time and over previous centuries, and who were genetically most similar to ancient individuals from France. These migrants contributed about half the ancestry of Iron Age people of England and Wales, thereby creating a plausible vector for the spread of early Celtic languages into Britain. These patterns are part of a broader trend of EEF ancestry becoming more similar across central and western Europe in the Middle to Late Bronze Age, coincident with archaeological evidence of intensified cultural exchange2-6. There was comparatively less gene flow from continental Europe during the Iron Age, and Britain's independent genetic trajectory is also reflected in the rise of the allele conferring lactase persistence to ~50% by this time compared to ~7% in central Europe where it rose rapidly in frequency only a millennium later. This suggests that dairy products were used in qualitatively different ways in Britain and in central Europe over this period.
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| 5. |
- Peric, Zoran, et al.
(författare)
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Quartz OSL dating of late quaternary Chinese and Serbian loess : A cross Eurasian comparison of dust mass accumulation rates
- 2019
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 502:Part A, s. 30-44
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Tidskriftsartikel (refereegranskat)abstract
- Reconstructing dust Mass Accumulation Rate (MAR) from loess deposits is critical to understanding past atmospheric mineral dust activity and requires accurate independent age models from loess deposits across Europe and Asia. Previous correlations of loess in Europe and China have tended to focus on multi-millennial timescales, with no detailed examination of dust MAR at the two ends of the Eurasian loess belt on shorter, sub-orbital scales. Here we present a detailed quartz optically stimulated luminescence (OSL) chronology from the Serbian Titel Loess Plateau (Veliki Surduk loess core) and the Chinese Loess Plateau (Lingtai section). The luminescence ages pass internal tests and show consistent increases in age with depth, with no obvious major hiatuses. However, as reported before, it seems the quartz OSL technique is only capable of accurate age determination up to accrued doses of ca. 150 Gy (ca. 30–40 ka) due to approaching field saturation of the quartz OSL signal. Two age-depth models were used to reconstruct dust MARs, where one utilises OSL data solely and the other additionally makes assumptions about sedimentation rates. Although short-term fluctuations in MAR are model dependent, general MAR patterns between the two sites are very similar, with peak MAR occurring rather late in the last glacial (ca. 13–25 ka). This suggests that at least broad scale trends in dust activity within the last glacial period may be similar at a continental scale.
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| 6. |
- Stevens, Thomas, 1979-, et al.
(författare)
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Ice-volume-forced erosion of the Chinese Loess Plateau global Quaternary stratotype site
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The International Commission on Stratigraphy (ICS) utilises benchmark chronostratigraphies to divide geologic time. The reliability of these records is fundamental to understand past global change. Here we use the most detailed luminescence dating age model yet published to show that the ICS chronology for the Quaternary terrestrial type section at Jingbian, desert marginal Chinese Loess Plateau, is inaccurate. There are large hiatuses and depositional changes expressed across a dynamic gully landform at the site, which demonstrates rapid environmental shifts at the East Asian desert margin. We propose a new independent age model and reconstruct monsoon climate and desert expansion/contraction for the last ~250 ka. Our record demonstrates the dominant influence of ice volume on desert expansion, dust dynamics and sediment preservation, and further shows that East Asian Summer Monsoon (EASM) variation closely matches that of ice volume, but lags insolation by ~5 ka. These observations show that the EASM at the monsoon margin does not respond directly to precessional forcing.
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| 7. |
- Újvári, Gábor, et al.
(författare)
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Coupled European and Greenland last glacial dust activity driven by North Atlantic climate
- 2017
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 114:50, s. E10632-E10638
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Tidskriftsartikel (refereegranskat)abstract
- Centennial-scale mineral dust peaks in last glacial Greenland ice cores match the timing of lowest Greenland temperatures, yet little is known of equivalent changes in dust-emitting regions, limiting our understanding of dust−climate interaction. Here, we present the most detailed and precise age model for European loess dust deposits to date, based on 125 accelerator mass spectrometry 14C ages from Dunaszekcső, Hungary. The record shows that variations in glacial dust deposition variability on centennial–millennial timescales in east central Europe and Greenland were synchronous within uncertainty. We suggest that precipitation and atmospheric circulation changes were likely the major influences on European glacial dust activity and propose that European dust emissions were modulated by dominant phases of the North Atlantic Oscillation, which had a major influence on vegetation and local climate of European dust source regions.
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| 8. |
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| 9. |
- Újvári,, Gabor, et al.
(författare)
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Stadial-interstadial temperature variations in East Central Europe preceding the Last Glacial Maximum
- 2021
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Ingår i: Paleoceanography and Paleoclimatology. - : American Geophysical Union (AGU). - 2572-4517 .- 2572-4525. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- Last glacial North Atlantic climate is characterized by abrupt, centennial-millennial scale climate oscillations, called Dansgaard-Oeschger (D-O) events. Understanding the cause and propagation of these D-O events into Eurasia is hampered by the scarcity of quantitative paleotemperature estimates from continental archives with precise, independent age models. Here, we present land snail shell carbonate clumped isotope-based active season paleotemperature estimates and δ13C/δ18O-based aridity reconstructions from Greenland stadial/interstadials (GS/GI) between 31 and 26.5 ka from the 14C-dated Dunaszekcső loess section (Hungary). This reconstruction is complemented with a new 230Th-dated flowstone stable isotope record covering 30-26 ka. Our snail shell clumped isotope (Δ47) data indicate growing season temperatures (GSTs) of 16°C–18°C and 7°C–14°C for the investigated interstadials and stadials, respectively. Stable carbon and oxygen stable isotope compositions of shells and flowstone calcite reveal milder interstadials with drier summers and more available moisture over the winter season, and colder stadials with annually/seasonally (winter) drier conditions, promoting increased loess/dust deposition. We propose that large-scale ocean-atmospheric variability, characterized by NAO phases, may have imparted a major control on transmitting abrupt North Atlantic climate event signals into continental Europe during the last glacial.
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| 10. |
- Újvári, Gábor, et al.
(författare)
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Two possible source regions for central Greenland last glacial dust
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:23
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Tidskriftsartikel (refereegranskat)abstract
- Dust in Greenland ice cores is used to reconstruct the activity of dust-emitting regions and atmospheric circulation. However, the source of dust material to Greenland over the last glacial period is the subject of considerable uncertainty. Here we use new clay mineral and < 10 mu m Sr-Nd isotopic data from a range of Northern Hemisphere loess deposits in possible source regions alongside existing isotopic data to show that these methods cannot discriminate between two competing hypothetical origins for Greenland dust: an East Asian and/or central European source. In contrast, Hf isotopes (< 10 mu m fraction) of loess samples show considerable differences between the potential source regions. We attribute this to a first-order clay mineralogy dependence of Hf isotopic signatures in the finest silt/clay fractions, due to absence of zircons. As zircons would also be absent in Greenland dust, this provides a new way to discriminate between hypotheses for Greenland dust sources.
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