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Youbin Sun - One of the best experts on this subject based on the ideXlab platform.
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late pliocene pleistocene changes in mass accumulation rates of Eolian Deposits on the central chinese loess plateau
Journal of Geophysical Research, 2005Co-Authors: Youbin SunAbstract:[1] Late Pliocene-Pleistocene changes in the mass accumulation rates (MARs) of Eolian Deposits on the central Chinese Loess Plateau (CLP) are reconstructed from measured bulk sediment densities combined with sedimentation rates calculated for two loess/red clay sequences. The reconstructed MARs demonstrate that over the past 3600 kyr, distinct aridity-humidity fluctuations occurred over glacial-interglacial timescales, and these were superimposed on a gradual long-term drying trend. Comparisons of the CLP MAR record with the MAR and δ18O records for marine sediments suggest that the development of Northern Hemisphere ice sheets since the late Pliocene has played a part in increasing the aridity of central Asia. In addition, the phased uplift of the Himalaya-Tibetan Plateau evidently had a profound influence on the aridity of central Asia; this was mediated by variations in the East Asian monsoonal circulation. Correlations among dust records from ice cores, marine sediments, and terrestrial loess over the last several glacial cycles provide compelling evidence that glacial periods are characterized by higher and more variable dust fluxes than interglacial intervals. Synchronous changes in the MAR, grain size, and δ18O records reveal dynamic linkages between Asian interior aridity, paleowind intensity, and ice volume after the onset of major Northern Hemisphere glaciations.
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Late Pliocene‐Pleistocene changes in mass accumulation rates of Eolian Deposits on the central Chinese Loess Plateau
Journal of Geophysical Research, 2005Co-Authors: Youbin SunAbstract:[1] Late Pliocene-Pleistocene changes in the mass accumulation rates (MARs) of Eolian Deposits on the central Chinese Loess Plateau (CLP) are reconstructed from measured bulk sediment densities combined with sedimentation rates calculated for two loess/red clay sequences. The reconstructed MARs demonstrate that over the past 3600 kyr, distinct aridity-humidity fluctuations occurred over glacial-interglacial timescales, and these were superimposed on a gradual long-term drying trend. Comparisons of the CLP MAR record with the MAR and δ18O records for marine sediments suggest that the development of Northern Hemisphere ice sheets since the late Pliocene has played a part in increasing the aridity of central Asia. In addition, the phased uplift of the Himalaya-Tibetan Plateau evidently had a profound influence on the aridity of central Asia; this was mediated by variations in the East Asian monsoonal circulation. Correlations among dust records from ice cores, marine sediments, and terrestrial loess over the last several glacial cycles provide compelling evidence that glacial periods are characterized by higher and more variable dust fluxes than interglacial intervals. Synchronous changes in the MAR, grain size, and δ18O records reveal dynamic linkages between Asian interior aridity, paleowind intensity, and ice volume after the onset of major Northern Hemisphere glaciations.
Jimin Sun - One of the best experts on this subject based on the ideXlab platform.
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Optical dating of Eolian Deposits since the last interglacial along the northern margin of the Chinese Loess Plateau
Journal of Asian Earth Sciences, 2018Co-Authors: Jimin Sun, Zhijun GongAbstract:Abstract Understanding the chronology of Eolian sand-loess-paleosol sequences along the northern margin of the Chinese Loess Plateau (CLP) is crucial for comprehending climate change and the advance and retreat of the adjacent Mu Us desert. In this study, a sand-loess-soil sequence from the northern margin of the CLP was studied by applying the single aliquot regenerative (SAR) protocol to quartz grains, and the multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocol to K-feldspar grains. For equivalent dose (De) determination, 63–90 μm quartz and K-feldspar grains were used. Our results indicate that the MET-pIRIR ages of K-feldspar grains in this sequence range from 94.4 ± 7.0 ka to 148.3 ± 13.3 ka for the last interglacial paleosol (S1); for the upper part of the section, quartz-based SAR-OSL dating was used, yielding ages spanning from 5.8 ± 0.4 ka to 35.9 ± 4.1 ka. After cross-checking these results with previously-reported isochron OSL and TL ages, the reliability of the MET-pIRIR protocol when applied to the last interglacial paleosol was confirmed. Based on a new OSL chronology of the Shimao profile, the studied Eolian Deposits can be broadly correlated with the last glacial-interglacial cycle, but their dating also points to sedimentary hiatuses occurring at 94.4 ka, 35.9 ka and 5.8 ka, due most probably to strong wind erosion caused by intensified cold-dry winter monsoonal circulations during the last glacial maxima.
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Luminescence sensitivities of quartz grains from Eolian Deposits in northern China and their implications for provenance
Quaternary Research, 2011Co-Authors: Jimin SunAbstract:article i nfo The thermoluminescence (TL) and optically stimulated luminescence (OSL) sensitivities of quartz grains from desertsand loess-redclaysequencesare usedtotrace Eolianprovenancesinnorthern China.Our results indicate that the 110°C TL peak and OSL sensitivities of quartz grains show differences among Chinese deserts, which can be subdivided into four groups according to the spatial variations of luminescence sensitivities. Such differences are related mostly to the regional difference in rock types of mountains surrounding or adjacent to the deserts. WealsoexaminethepossibleprovenancechangesbetweentheQuaternaryloessandtheTertiaryEolianredclay, and the results indicate that the luminescence sensitivity of Tertiary red clay is higher than that of Quaternary loess (L1, L15, and L33), implying source materials of the Eolian Deposits changed relative to those of the Quaternary.
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late oligocene miocene mid latitude aridification and wind patterns in the asian interior
Geology, 2010Co-Authors: Jimin Sun, Zhenqing Zhang, Weiming Liu, Jin MengAbstract:The Asian interior has the largest mid-latitude arid zone in the Northern Hemisphere, and so has become increasingly attractive for studying the initiation and the past extent of aridification in this zone. Given the enormousness of the Asian interior, it remains unclear how old and extensive the Eolian Deposits might have been, and what wind regimes have been responsible for the formation of the mid-latitude arid zone. Here we report new Eolian records of widespread Tertiary Eolian Deposits in a region far from the Chinese Loess Plateau, the giant Junggar inland basin of northwestern China. Our results demonstrate that the earliest Eolian deposition initiated ca. 24 Ma. We interpret that the Tertiary Eolian dust in the Junggar Basin was transported by westerly winds, possibly from areas in Kazakhstan; the dust differs from the airborne dust transported by winter monsoon winds from the deserts of Mongolia and northern China that accumulated on the Loess Plateau. These results further reveal that the climate pattern, similar to that of the present, has prevailed at least since the latest Oligocene in Central Asia.
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Temporal variations in Pb isotopes and trace element concentrations within Chinese Eolian Deposits during the past 8 Ma: Implications for provenance change
Earth and Planetary Science Letters, 2010Co-Authors: Jimin Sun, Xiangkun ZhuAbstract:article i nfo The Pb isotopes and trace element compositions of the silicate fraction of airborne dust from the Chinese Loess Plateau were analyzed to infer provenance change during the past 8 Ma. The results indicate that the composition of Eolian dust changed at 2.6 Ma, coincident with initiation of the Northern Hemisphere ice sheet. The change in trace element composition at 2.6 Ma indicates that a larger component of the Eolian dust was derived from felsic rocks after this time. Pb isotopic evidence demonstrates that the source material of Tertiary Red Clay differs to some extent from that of Quaternary Eolian Deposits. Although chemical weathering may result in compositional changes in Eolian Deposits, such a scenario is not supported by the present evidence. Given that glacial grinding and frost-weathering processes have been active in the peaks of high mountains during the Quaternary, Eolian dust of this age contains a large proportion of material derived from areas of high topographic relief and relatively little material from low-lying cratonic regions. Such alpine processes played an important role in controlling the distinct changes in Pb isotopes and trance element concentrations recorded at around 2.6 Ma. © 2010 Published by Elsevier B.V.
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Nd and Sr isotopic variations in Chinese Eolian Deposits during the past 8 Ma: Implications for provenance change
Earth and Planetary Science Letters, 2005Co-Authors: Jimin SunAbstract:A record of changes in Nd and Sr isotopic composition of the Eolian Deposits from the central Loess Plateau has been determined for the past 8 Ma. The isotopic records of the silicate fraction of the Quaternary and Tertiary Eolian Deposits allow interpreting the interplay between the Sr isotopic variations in the Eolian Deposits and the late Cenozoic tectonic and climatic changes. The results indicate that the temporal variations of Nd and Sr isotopes show remarkable changes around the beginning of the Quaternary. The lower values of the 143 Nd/ 144 Nd and the decreasing trend of the 87 Sr/ 86 Sr ratios after 2.58 Ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late Cenozoic uplift induced glacial grinding in the high orogenic belts in central Asia. In this context, the substantial changes in climate and tectonics have modified dust sources significantly, and the Quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the Tertiary Red Clay. D 2005 Elsevier B.V. All rights reserved.
Zhengtang Guo - One of the best experts on this subject based on the ideXlab platform.
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Neogene Eolian Deposits within the West Qinling Mountains:Climatic and tectonic implications
Chinese Science Bulletin, 2010Co-Authors: Zhengtang GuoAbstract:The Qinling Mountains constitute a key climate barrier between southern and northern China. Our recent investigations revealed widely spread Eolian Deposits of Neogene age mantling the piedmont highlands of the intermountain basins within West Qinling. Micro-mammalian fossils dated a 150.2 m section (NL-VI) near Xihe for the late Miocene to Pliocene (∼10–4 Ma). Soil micromorphology, grain-size and geochemical analysis consistently define typical loess-soil alternations for the upper (0–66 m) and lower (98–150.2 m) parts of the section, with the middle section (66–98 m) having been affected by episodic slope erosions. These results add important insights to the earlier studies about the widespread Eolian deposition in northern China during the Miocene, prior to 8 Ma. They also suggest that the basic configuration of the ridges and inter-ridge basins of West Qinling has already formed by ∼10 Ma. The well-preserved Eolian Deposits are unlikely to support intense substratum deformation and rapid uplift of West Qinling since the late Miocene.
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Geochemical characteristics of the Miocene Eolian Deposits in China: Their provenance and climate implications
Geochemistry Geophysics Geosystems, 2009Co-Authors: Meiyan Liang, Zhengtang Guo, A. Julia Kahmann, Frank OldfieldAbstract:[1] In the Loess Plateau in northern China, the Quaternary loess-soil sequences, the Hipparion Red Earth of Eolian origin (Red Clay), and the Miocene loess-soil sequences constitute a near-continuous terrestrial record of paleoclimates for the past 22 Ma. In this study, Miocene loess and paleosol samples from Qinan (QA-I) were analyzed for their major, trace, and rare earth element chemistry and compared with the PlioPleistocene samples from Xifeng with emphasis on their provenance and paleoclimatic implications. The results show similar geochemical signatures for the Eolian Deposits of different ages, and they are also comparable to the average composition of the upper continental crust. These suggest that the dust materials were all derived from well-mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes. They also support the notion of broadly similar source areas and dust-transporting trajectories for different periods since the early Neogene. The slightly higher K2O, Fe2O3, and MgO concentrations and loss on ignition values and the lower Na2O content in the Miocene loess samples compared to their Quaternary counterparts are attributable to the finer grain size of the Miocene loess associated with weaker dust-carrying winds. In comparison with some loess in Europe and America with less extensive sources, Eolian Deposits from northern China show higher Cs and lower Zr and Hf content. This is attributable to the sorting processes from remoter sources during transportation and could be regarded as an indication of the desert origin of the loess Deposits. Miocene paleosol samples show higher chemical index of alteration values and lower CaO, MgO, and Na2O concentrations than does the intervening loess, indicating stronger weathering of the paleosols. However, the moderate chemical weathering of the paleosol samples indicates a constant semiarid and subhumid climatic range in northern China since the early Miocene. Components: 9791 words, 8 figures, 3 tables.
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Magnetostratigraphy of a late Miocene‐Pliocene loess‐soil sequence in the western Loess Plateau in China
Geophysical Research Letters, 2004Co-Authors: Qingzhen Hao, Zhengtang GuoAbstract:[1] Eolian Deposits of Pliocene age have never been reported from the western Loess Plateau in China. Here, a 73.7 m Eolian sequence is dated using magnetostratigraphic method and micromammalian fossils. The polarity zonation correlates with the geomagnetic polarity timescale (GPTS), from Chron 3Br.1r to Chron 2An.3n, indicating an age from 7.10 to 3.52 Ma BP. The sequence is characterized by clear expression of eighty-four pairs of loess and soil layers while individual soils are basically indefinable for the Eolian Deposits of the same age in the eastern Loess Plateau, suggesting that the later has experienced other geological processes. This sequence extends the upper limit of the previously reported Miocene loess-soil sequences at Qinan into the Pliocene, about 3.52 Ma BP.
Zhongli Ding - One of the best experts on this subject based on the ideXlab platform.
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drastic climatic shift at 2 8ma as recorded in Eolian Deposits of china and its implications for redefining the pliocene pleistocene boundary
Quaternary International, 2010Co-Authors: Shiling Yang, Zhongli DingAbstract:There has been a long-running debate over the position of the Pliocene-Pleistocene boundary, i.e. 1.8 Ma versus 2.6 Ma. This study presents litho- and pedo-stratigraphic characteristics, grain size, magnetic susceptibility, and dust sedimentation rates for ‘red clay’-loess sequences over northern China, in order to assess the drastic climatic event(s) recorded in the quasi-continuous Eolian Deposits, and to readdress the position of the Pliocene-Pleistocene boundary. In complete Chinese loess sequences, 33 soil-loess couplets have been identified and labeled with Si-Li system. Traditionally, the base of Chinese loess has been designated at the bottom of loess unit L33. However, a typical loess layer within the uppermost ‘red clay’ is identified and formally designated here as L34 and the soil unit between L33 and L34 as S33, which lowers the basal age of Chinese loess from 2.6 Ma to w2.8 Ma. Although the Neogene ‘red clay’ and the overlying Quaternary loess are both of windblown origin, they have quite different pedogenic characteristics. The loess consists of alternating reddish soil and yellowish loess layers, while the ‘red clay’ is composed of soils with much redder colour and carbonate nodule layers. In general, the ‘‘red clay’’ has been subjected to stronger pedogenic processes than the overlying loess, and can be regarded as an extremely thick soil complex. The alternation of loess and soils reflects large-scale oscillations between glacial and interglacial conditions, whereas the well-developed ‘red clay’ deposition indicates a relatively stable climate condition. At w2.8 Ma, shortly before the Gauss/Matuyama boundary, the Eolian sequences show a sedimentary transition from the well-weathered ‘red clay’ to the alternating loess and paleosol Deposits, accompanied by coarser particle size, increased dust accumulation rates, and change of magnetic susceptibility signature. These indicate a large climatic shift from long-lasting warm-humid conditions to large-amplitude cold-dry and warm-humid fluctuations around 2.8 Ma, and a dramatic increase in aridity over the dust source region. In contrast, such a drastic event is not identified around the top of the Olduvai event or at any other time of the past 7.7 Ma. As the Gauss/Matuyama boundary offers a sound foundation for global time correlation and chronostratigraphic classification, these results still support the proposal of ICS and INQUA, that the conventional Pliocene-Pleistocene boundary should be lowered from 1.8 Ma to 2.6 Ma.
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Drastic climatic shift at ̃2.8Ma as recorded in Eolian Deposits of China and its implications for redefining the Pliocene-Pleistocene boundary
Quaternary International, 2009Co-Authors: Shiling Yang, Zhongli DingAbstract:There has been a long-running debate over the position of the Pliocene-Pleistocene boundary, i.e. 1.8 Ma versus 2.6 Ma. This study presents litho- and pedo-stratigraphic characteristics, grain size, magnetic susceptibility, and dust sedimentation rates for ‘red clay’-loess sequences over northern China, in order to assess the drastic climatic event(s) recorded in the quasi-continuous Eolian Deposits, and to readdress the position of the Pliocene-Pleistocene boundary. In complete Chinese loess sequences, 33 soil-loess couplets have been identified and labeled with Si-Li system. Traditionally, the base of Chinese loess has been designated at the bottom of loess unit L33. However, a typical loess layer within the uppermost ‘red clay’ is identified and formally designated here as L34 and the soil unit between L33 and L34 as S33, which lowers the basal age of Chinese loess from 2.6 Ma to w2.8 Ma. Although the Neogene ‘red clay’ and the overlying Quaternary loess are both of windblown origin, they have quite different pedogenic characteristics. The loess consists of alternating reddish soil and yellowish loess layers, while the ‘red clay’ is composed of soils with much redder colour and carbonate nodule layers. In general, the ‘‘red clay’’ has been subjected to stronger pedogenic processes than the overlying loess, and can be regarded as an extremely thick soil complex. The alternation of loess and soils reflects large-scale oscillations between glacial and interglacial conditions, whereas the well-developed ‘red clay’ deposition indicates a relatively stable climate condition. At w2.8 Ma, shortly before the Gauss/Matuyama boundary, the Eolian sequences show a sedimentary transition from the well-weathered ‘red clay’ to the alternating loess and paleosol Deposits, accompanied by coarser particle size, increased dust accumulation rates, and change of magnetic susceptibility signature. These indicate a large climatic shift from long-lasting warm-humid conditions to large-amplitude cold-dry and warm-humid fluctuations around 2.8 Ma, and a dramatic increase in aridity over the dust source region. In contrast, such a drastic event is not identified around the top of the Olduvai event or at any other time of the past 7.7 Ma. As the Gauss/Matuyama boundary offers a sound foundation for global time correlation and chronostratigraphic classification, these results still support the proposal of ICS and INQUA, that the conventional Pliocene-Pleistocene boundary should be lowered from 1.8 Ma to 2.6 Ma.
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Deposits and soils of the past 130 000 years at the desert loess transition in northern china
Quaternary Research, 1998Co-Authors: Zhongli DingAbstract:The desert–loess transitional zone in north-central China has long been thought sensitive to Quaternary climatic change. However, reconstruction of Quaternary climates in this area has been hindered by incompleteness of geological sections. Here we report the analytical results of two recently found sand–loess–soil sections. Both sections have thick Eolian Deposits from the last interglacial–glacial cycle and can be correlated with one another. Field observations, thermoluminescence dating, and other laboratory analyses show that the last interglacial period produced three paleosols and two intercalated loess layers. Loess from the last glacial period is interbedded with three sand horizons that represent desert extension. The expansion and contraction of desert in northern China may have been forced by the east Asia monsoon.
Zhong Chen - One of the best experts on this subject based on the ideXlab platform.
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evolving sources of Eolian detritus on the chinese loess plateau since early miocene tectonic and climatic controls
Earth and Planetary Science Letters, 2013Co-Authors: Zhong ChenAbstract:Abstract The thick Deposits of Eolian dust on the Chinese Loess Plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations. Here we report a 22 Ma-long Nd and Sr isotopic records of the Eolian sources. Decreasing e Nd values and increasing 86 Sr/ 87 Sr ratios of the Eolian Deposits has been observed from early Miocene to about 7 Ma, which indicates growing material contribution from Qilian Mountains relative to the Gobi Altay Mountains. The source shift during 22–7 Ma is interpreted to reflect the erosional response of the Qilian Mountains to its surface uplift. Between 7 Ma and 1.2 Ma, the results show relative constant Nd and Sr isotopic compositions of the Eolian Deposits, and thus suggest a constant source contribution between Qilian Mountains and Gobi Altay Mountains. Synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution. Since 1.2 Ma, Nd and Sr isotopic records indicate that the relative debris input from Qilian Mountains drops rapidly. As large-scale topographic changes would not be expected in such a short time period, the source shift since 1.2 Ma might be by the differing erosional responses in Qilian Mountains and Gobi Altay Mountains to the development of full glacial climate after the middle Pleistocene transition. This work shows that combined Nd and Sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale.