Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus pro...Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate展开更多
Analyses of paleomagnetic polarity reversals, magnetic susceptibility and grain size on the red clay-loess sequence, about 280 m thick, at Jingbian show that this sequence contains most of the stratigraphic units reco...Analyses of paleomagnetic polarity reversals, magnetic susceptibility and grain size on the red clay-loess sequence, about 280 m thick, at Jingbian show that this sequence contains most of the stratigraphic units recorded in the standard red clay-loess sections of the Loess Plateau over the past 3.5 Ma. Using sand particle percentage ( 】 63 μm%) of the eolian sequence as a proxy indicator of desert extent and aridity in the dust source regions, it is found that during the past 3.5 Ma, there are three important climatic events indicating the advance of the Mu Us Desert. The events occurred at about 2.6, 1.1 and 0.6 MaBP, respectively. The stepwise advance of the Mu Us Desert may be linked closely to increase in global ice volume and uplift of the Tibetan Plateau in the late Cenozoic.展开更多
lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic ...lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) C<sub>4</sub> plants might be present at least by7.0 Ma; ( ⅱ ) C<sub>4</sub> plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C<sub>4</sub> vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal展开更多
Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root trace...Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root traces and contain the traces of stele that can be used as the definite evidence of root traces. Surrounding the worm-shaped veins there are some micro-features pressed by past root growth. Geochemical analyses indicate that the white part in the WSV was depleted in Fe content. These lines of evidence suggest the WSVs in the red earth of South China are the root traces of past forest.展开更多
Changes in biodiversity during periods of global warming are of broad public concern.To study the effect of the warming process on the ecosystem,we carried out pollen analyses on samples from seven selected sections a...Changes in biodiversity during periods of global warming are of broad public concern.To study the effect of the warming process on the ecosystem,we carried out pollen analyses on samples from seven selected sections at Qingyang,Ningxian,Yangling,Binxian,Baoji,Yanshi,and Lingbao on the Chinese Loess Plateau in order systematically to evaluate changes in plant diversity since the Last Glacial Maximum(LGM).The plant richness indices(Simpson’s diversity index and rarefaction analysis)indicated that the plant diversity of each section increased during the process of warming from the LGM to the Holocene Optimum,especially at Baoji and Lingbao.These results are consistent with many long-timescale geological records,which show that warming can increase biodiversity;therefore,the popular viewpoint that warming leads to biodiversity loss or species extinction needs to be re-examined.展开更多
Detailed rock-magnetic and paleomagnetic investigations have been carried out in a loess-paleosol sequence from the lower part ot unit S9 to the bottom of L11 at Jingbian (37.4° N, 108.8°E), which demonstrat...Detailed rock-magnetic and paleomagnetic investigations have been carried out in a loess-paleosol sequence from the lower part ot unit S9 to the bottom of L11 at Jingbian (37.4° N, 108.8°E), which demonstrates that the Upper Jaramillo polarity reversal and a short geomagnetic event bounded within the Jaramillo normal subchron have been revealed. The duration of this short event was about 8.5 ka. The statistical analysis showed that the virtual geomagnet-展开更多
A weakly developed paleosol was identified at S1-L1 transition of the loess section of Zhaitang, Beijing. This paleosol may represent a climatic reversal which is associated with the strengthening in summer monsoon an...A weakly developed paleosol was identified at S1-L1 transition of the loess section of Zhaitang, Beijing. This paleosol may represent a climatic reversal which is associated with the strengthening in summer monsoon and correlated well with the climatic regression event documented in the paleoclimate records from Greenland ice, marine sediments and European pollen at the last interglacial-last glacial transition.展开更多
In the transitional region between the Loess Plateau and deserts, 4 sections located respectively at Yuling, Hengshan, Dingbian and Huining of China are studied. The high-resolution paleoclimatic records obtained show...In the transitional region between the Loess Plateau and deserts, 4 sections located respectively at Yuling, Hengshan, Dingbian and Huining of China are studied. The high-resolution paleoclimatic records obtained show that environmental events on varying time scales have happened over East Asia. These events are dated with the time scales established using the recently-developed approach of Automatic Orbital Tuning. This leads to the establishment of the chronology of the environmental events.展开更多
Based on the climate records derived from loess deposits in north-central China, the characteristics of the East-Asia paleomonsoonal changes during the Late Pleistocene are summarized as follows: (ⅰ) The 0.1_Ma clima...Based on the climate records derived from loess deposits in north-central China, the characteristics of the East-Asia paleomonsoonal changes during the Late Pleistocene are summarized as follows: (ⅰ) The 0.1_Ma climate period is predominant in both summer and winter monsoonal changes over East Asia; (ⅱ) The East-Asia monsoonal variation is different from the Indian monsoon during the Late Pleistocene; (ⅲ) There is a ~5_ka time lag of the East-Asia monsoon changes relative to the theoretically calculated solar radiation changes; (ⅳ) There is a general trend toward increase in winter monsoon and decrease in summer monsoon in the last glaciation; (ⅴ) In the East-Asia monsoonal region, the amplitude of glacial-to-interglacial cycles shows a remarkable increase from south to north. To explain these characteristics, a conceptual model is developed and the forcing of global ice volume variations in the monsoonal history is emphasized.展开更多
基金the National Natural Science Foundation of China (Grant No. 49525203).
文摘Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate
文摘Analyses of paleomagnetic polarity reversals, magnetic susceptibility and grain size on the red clay-loess sequence, about 280 m thick, at Jingbian show that this sequence contains most of the stratigraphic units recorded in the standard red clay-loess sections of the Loess Plateau over the past 3.5 Ma. Using sand particle percentage ( 】 63 μm%) of the eolian sequence as a proxy indicator of desert extent and aridity in the dust source regions, it is found that during the past 3.5 Ma, there are three important climatic events indicating the advance of the Mu Us Desert. The events occurred at about 2.6, 1.1 and 0.6 MaBP, respectively. The stepwise advance of the Mu Us Desert may be linked closely to increase in global ice volume and uplift of the Tibetan Plateau in the late Cenozoic.
文摘lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) C<sub>4</sub> plants might be present at least by7.0 Ma; ( ⅱ ) C<sub>4</sub> plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C<sub>4</sub> vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal
文摘Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root traces and contain the traces of stele that can be used as the definite evidence of root traces. Surrounding the worm-shaped veins there are some micro-features pressed by past root growth. Geochemical analyses indicate that the white part in the WSV was depleted in Fe content. These lines of evidence suggest the WSVs in the red earth of South China are the root traces of past forest.
基金supported by the National Basic Research Program of China(2010CB950204)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA05120204)
文摘Changes in biodiversity during periods of global warming are of broad public concern.To study the effect of the warming process on the ecosystem,we carried out pollen analyses on samples from seven selected sections at Qingyang,Ningxian,Yangling,Binxian,Baoji,Yanshi,and Lingbao on the Chinese Loess Plateau in order systematically to evaluate changes in plant diversity since the Last Glacial Maximum(LGM).The plant richness indices(Simpson’s diversity index and rarefaction analysis)indicated that the plant diversity of each section increased during the process of warming from the LGM to the Holocene Optimum,especially at Baoji and Lingbao.These results are consistent with many long-timescale geological records,which show that warming can increase biodiversity;therefore,the popular viewpoint that warming leads to biodiversity loss or species extinction needs to be re-examined.
文摘Detailed rock-magnetic and paleomagnetic investigations have been carried out in a loess-paleosol sequence from the lower part ot unit S9 to the bottom of L11 at Jingbian (37.4° N, 108.8°E), which demonstrates that the Upper Jaramillo polarity reversal and a short geomagnetic event bounded within the Jaramillo normal subchron have been revealed. The duration of this short event was about 8.5 ka. The statistical analysis showed that the virtual geomagnet-
文摘A weakly developed paleosol was identified at S1-L1 transition of the loess section of Zhaitang, Beijing. This paleosol may represent a climatic reversal which is associated with the strengthening in summer monsoon and correlated well with the climatic regression event documented in the paleoclimate records from Greenland ice, marine sediments and European pollen at the last interglacial-last glacial transition.
文摘In the transitional region between the Loess Plateau and deserts, 4 sections located respectively at Yuling, Hengshan, Dingbian and Huining of China are studied. The high-resolution paleoclimatic records obtained show that environmental events on varying time scales have happened over East Asia. These events are dated with the time scales established using the recently-developed approach of Automatic Orbital Tuning. This leads to the establishment of the chronology of the environmental events.
文摘Based on the climate records derived from loess deposits in north-central China, the characteristics of the East-Asia paleomonsoonal changes during the Late Pleistocene are summarized as follows: (ⅰ) The 0.1_Ma climate period is predominant in both summer and winter monsoonal changes over East Asia; (ⅱ) The East-Asia monsoonal variation is different from the Indian monsoon during the Late Pleistocene; (ⅲ) There is a ~5_ka time lag of the East-Asia monsoon changes relative to the theoretically calculated solar radiation changes; (ⅳ) There is a general trend toward increase in winter monsoon and decrease in summer monsoon in the last glaciation; (ⅴ) In the East-Asia monsoonal region, the amplitude of glacial-to-interglacial cycles shows a remarkable increase from south to north. To explain these characteristics, a conceptual model is developed and the forcing of global ice volume variations in the monsoonal history is emphasized.