The Experts below are selected from a list of 14298 Experts worldwide ranked by ideXlab platform
Zhengtang Guo - One of the best experts on this subject based on the ideXlab platform.
-
magnetostratigraphy of the xihe Loess Soil sequence and implication for late neogene deformation of the west qinling mountains
Geophysical Journal International, 2012Co-Authors: Zhengtang Guo, Chenglong Deng, Tao Zhan, Zhengquan Yao, Frank OldfieldAbstract:SUMMARY TheQinlingMountainrangeformsanimportantclimatebarrierbetweensouthernandnorthern China. Its western part, referred to as the West Qinling, constitutes a unit of northeastern Tibetan Plateau. The uplift history of Qinling during the Neogene is still a contentious issue. Magnetostratigraphic results from the 150-m-thick Xihe Loess-Soil sequence (NL-VI), located on the alluvial highlands surrounding an intermontane basin from the West Qinling, indicate 17 reverse and 17 normal magnetozones. They are correlative with the interval from chron C5n to chron C2Ar in the Geomagnetic Polarity Timescale. The age of the NL-VI section can thus be palaeomagnetically constrained to a period from 10.5 to 4.2 Ma. The middle portion of the section has been affected intermittently by surface erosion processes. As Loess is sensitive to any erosion that may have been induced by substratum deformation and tectonic uplift, this sequence indicates that the intermontane basin–ridge pattern of the West Qinling had already been formed by 10.5 Ma, thus providing suitable topographic conditions for aeolian deposition. This timing is consistent with a significant deformation phase between ∼14 and 10 Ma reported for the Tibetan Plateau. Meanwhile, the complete preservation of the NL-VI Loess-Soil sequence precludes both intense deformation of the substrate and rapid uplift of the West Qinling between 10.5 and 4.2 Ma. Although the erosion-affected portion of the NL-VI section reflects some degree of tectonic instability from 8.3 to 6.9 Ma, the intensity must have been sufficiently weak to prevent the erosion of the aeolian deposits. These further suggest that the late Miocene growth of the Tibetan Plateau has not significantly affected the West Qinling. Thus, the studied NL-VI aeolian sequence provides not only independent evidence for the uplift history of the West Qinling within an accurate chronological framework, but also provides new insights into the tectonic changes on the northeastern Tibetan Plateau.
-
magnetostratigraphy of an early middle miocene Loess Soil sequence in the western Loess plateau of china
Geophysical Research Letters, 2007Co-Authors: Qingzhen Hao, Zhengtang GuoAbstract:[1] Stratigraphy and magnetic susceptibility of the Quaternary eolian deposits at different sites in China can be closely correlated, confirming their spatial coherence and temporal continuity. The extent to which these conclusions are true for the Miocene Loess-Soil sequences remains to be addressed. Here, a 231.9-m eolian section, QA-III, is geomagnetically dated, yielding an age span of 21.4–11.4 Ma, with the portion older than 19.6 Ma being partially water-reworked. The magnetozones, litholigic structure and magnetic susceptibility of the sequence are highly correlative with the QA-I and QA-II sections, 30 km west of QA-III. These sequences demonstrate that the Miocene Loess deposits are also spatially correlative in stratigraphy, present a near-continuous sequence of paleoenvironment changes, and that magnetic susceptibility is a useful tool for stratigraphic correlation. The basal age of QA-III confirms again the onset of Asian inland deserts and monsoon-dominate climates by the early Miocene.
-
eolian origin of the miocene Loess Soil sequence at qin an china evidence of quartz morphology and quartz grain size
Chinese Science Bulletin, 2006Co-Authors: Jinfeng Liu, Zhengtang Guo, Yansong Qiao, Qingzheng Hao, Baoyin YuanAbstract:Recent study revealed that the so-called Neogene Gansu System in the western Loess Plateau contains Loess-Soil sequences of Miocene age. A most complete sequence (QA-I) covers a time interval from ~22 to ~6.2 Ma BP, consisting of more than 230 visually definable paleosols interbedded with Loess layers. A Loess-Soil sequence of late Miocene-Pliocene age, synchronous with the Hipparian Red Clay in the eastern Loess Plateau, was also recognized, and extends the Miocene sequences into the Pliocene, ~3.5 Ma BP. Recently, Miocene eolian deposits were also reported from the high terraces near Xining. Eolian origin of the Miocene sequences near Qin’an is supported by several lines of evidence, including micromorphological, sedimentological and geochemical data. Here, we further examine the morphology and sedimentological characteristics of more samples covering the entire QA-I sequence, to provide additional evidence of the eolian origin. Quartz is a dominant mineral component of eolian dust deposits . Because of its stable physical and chemical properties under surface conditions, grain morphology of the quartz is usually used to determine the sources, transportation dynamics and postdepositional modifications of the sediments . Grain-size of the quartz fraction is also better reflective to that of the original eolian dust as quartz is resistant to postdepositional chemical weathering in the semi-arid/ semi-humid Loess regions. In this study, grainmorphology and grain-size distributions of the quartz fraction from the QA-I sequence are examined, and compared with those of the typical eolian deposits of Quaternary age from the Xifeng site.
-
late miocene pliocene development of asian aridification as recorded in the red earth formation in northern china
Grid and Pervasive Computing, 2004Co-Authors: Zhengtang Guo, Qingzhen Hao, Shuzhen Peng, Pierre E Biscaye, Tungsheng LiuAbstract:In northern China, the Late Miocene–Pliocene Hipparion Red-Earth Formation in the eastern Loess Plateau fills a gap of climate records between the well-known Loess-Soil sequences of the last 2.6 Ma and the Miocene Loess-Soil sequences from the western Loess Plateau. Earlier studies on type sections indicate that a major part of the Red-Earth Formation is also of windblown origin, covering the period from f7–8 tof2.6 Ma BP. Because the eolian dust deposited in the region originated from the Asian desert lands, the Red-Earth must contain a record of the aridification history of the Asian interior. In this study, the Xifeng type section in the eastern Loess Plateau is studied to assess the development of Asian aridification during Late Miocene–Pliocene time. Eolian dust deposition continued at the central Loess Plateau since f6.2 Ma BP, indicating that sizable desert lands in the interior of Asia and the Asian winter monsoon must have been constantly maintained during Late Miocene–Pliocene time, and were able to provide a significant amount of eolian dust. The aridity in the source areas was stronger from f6.2 to f5 Ma BP and weaker from f 5t of3.6 Ma BP. Two major aridification steps are observed at f3.6 and f2.6 Ma BP, respectively. The intensification of eolian deposition at f3.6 Ma BP is synchronous with a suggested uplift of portions of the Tibetan Plateau. The general aridification history is also highly consistent with the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets during this interval. Our results therefore suggest that both Tibetan uplift and ice-building processes in the northern hemisphere were two prominent driving forces behind the long-term desertification in the interior of Asia during Late Miocene and Pliocene time. D 2004 Elsevier B.V. All rights reserved.
-
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.
Tungsheng Liu - One of the best experts on this subject based on the ideXlab platform.
-
late miocene pliocene development of asian aridification as recorded in the red earth formation in northern china
Grid and Pervasive Computing, 2004Co-Authors: Zhengtang Guo, Qingzhen Hao, Shuzhen Peng, Pierre E Biscaye, Tungsheng LiuAbstract:In northern China, the Late Miocene–Pliocene Hipparion Red-Earth Formation in the eastern Loess Plateau fills a gap of climate records between the well-known Loess-Soil sequences of the last 2.6 Ma and the Miocene Loess-Soil sequences from the western Loess Plateau. Earlier studies on type sections indicate that a major part of the Red-Earth Formation is also of windblown origin, covering the period from f7–8 tof2.6 Ma BP. Because the eolian dust deposited in the region originated from the Asian desert lands, the Red-Earth must contain a record of the aridification history of the Asian interior. In this study, the Xifeng type section in the eastern Loess Plateau is studied to assess the development of Asian aridification during Late Miocene–Pliocene time. Eolian dust deposition continued at the central Loess Plateau since f6.2 Ma BP, indicating that sizable desert lands in the interior of Asia and the Asian winter monsoon must have been constantly maintained during Late Miocene–Pliocene time, and were able to provide a significant amount of eolian dust. The aridity in the source areas was stronger from f6.2 to f5 Ma BP and weaker from f 5t of3.6 Ma BP. Two major aridification steps are observed at f3.6 and f2.6 Ma BP, respectively. The intensification of eolian deposition at f3.6 Ma BP is synchronous with a suggested uplift of portions of the Tibetan Plateau. The general aridification history is also highly consistent with the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets during this interval. Our results therefore suggest that both Tibetan uplift and ice-building processes in the northern hemisphere were two prominent driving forces behind the long-term desertification in the interior of Asia during Late Miocene and Pliocene time. D 2004 Elsevier B.V. All rights reserved.
-
geochemistry of the pliocene red clay formation in the chinese Loess plateau and implications for its origin source provenance and paleoclimate change
Geochimica et Cosmochimica Acta, 2001Co-Authors: Zhongli Ding, Jimin Sun, Shiling Yang, Tungsheng LiuAbstract:Abstract Recent field observations and sedimentological studies suggest the eolian origin of the late Tertiary red clay formation underlying the Pleistocene Loess-Soil sequence in the Loess Plateau, thereby extending the wind-blown record from ∼2.6 Ma down to ∼7.0 Ma in north-central China. To address the source provenance of the red clay, major and trace element concentrations were analyzed on the samples from a north-south Loess transect of the Loess Plateau and a red clay section at Jiaxian. Results show that there is a good agreement of both major and trace element compositions between the last glacial-interglacial Loess-Soil units and the Jiaxian red clay record. The REE distribution patterns of the Loess-Soil and red clay samples are remarkably similar in shape, with enriched LREE and fairly flat HREE profiles and clear negative Eu anomaly. The geochemical features of the red clay are also identical to those of upper continental crust. These chemical characteristics provide further evidence for eolian sedimentation of the red clay. From the relations both between Na2O/Al2O3 and K2O/Al2O3 ratios and between U/Pb and Th/Pb ratios, the eolian Loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area. The chemical similarity between Soil unit S1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern China during the late Tertiary. Comparison of down-section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that CaO/Al2O3, Sr/Rb and Sr/Ba are more sensitive to climate changes than magnetic susceptibility, and can be used to reconstruct the climate history of the late Cenozoic.
-
summer monsoon variations over the last 1 2 ma from the weathering of Loess Soil sequences in china
Geophysical Research Letters, 2000Co-Authors: Zhengtang Guo, Shuzhen Peng, Pierre E Biscaye, Lanying Wei, Xihui Chen, Tungsheng LiuAbstract:The Loess-Soil sequence in northern China contains a near continuous record of Quaternary paleoclimate. Magnetic susceptibility and grain size have so far been the only proxies available to address the long-term changes of the East-Asian paleomonsoon extending back to more than one million years. In this study, the ratio of CBD (citrate-bicarbonate-dithionite)-extractable free Fe2O3 (FeD), a measure of iron liberated by chemical weathering, versus the total Fe2O3 available (FeT) was measured on samples at 10 cm intervals taken from two Loess sections deposited over the last 1.2 Ma. Variations of this index are highly consistent with other pedological indicators, but in addition provide a quantitative measurement of the degree of pedogenesis in the Loess Plateau. Since chemical weathering in the region mainly depends upon summer precipitation and temperature, weathering intensity primarily reflects changes in the East-Asian summer monsoon. The new proxy has been used to document a series of summer monsoon changes of global significance, which are not necessarily recorded by magnetic susceptibility.
Zhongli Ding - One of the best experts on this subject based on the ideXlab platform.
-
pleistocene chemical weathering history of asian arid and semi arid regions recorded in Loess deposits of china and tajikistan
Geochimica et Cosmochimica Acta, 2006Co-Authors: Shiling Yang, Feng Ding, Zhongli DingAbstract:Quaternary Loess–Soil sequences in China and Tajikistan are valuable archives of the chemical weathering history for arid and semiarid regions of Asia. The development of new proxies independent of grain size are vital to reconstruct the long-term chemical weathering history of eolian deposits. In this study, we analyze major elemental and Rb, Sr, and Ba concentrations of decarbonated residue from representative Loess and Soil units along a north–south transect on the Chinese Loess Plateau and compare these concentrations among different grain-size fractions. Results show that most of the elemental abundances and ratios vary considerably among different grain-size fractions for both Loess and paleosols, indicating transport-driven compositional differentiation of minerals during subaerial transport. However, (CaO + Na2O + MgO)/TiO2 ratios show little variation among different size fractions for the Loess–Soil transect. Loess–Soil sequences at Lingtai (northern China) and Chashmanigar (southern Tajikistan) for the past 1.50–1.77 Ma show lower (CaO + Na2O + MgO)/TiO2 ratios in Soil units than in adjacent Loess horizons, in good agreement with greater weathering intensity in Soils than in Loess units. The (CaO + Na2O + MgO)/TiO2 ratio of the decarbonated residue is therefore a reliable proxy for chemical weathering of Loess deposits that is independent of grain size. The (CaO + Na2O+MgO)/TiO2 ratios of the Lingtai and Chashmanigar sections display a relatively regular oscillation within a narrow range in the early Pleistocene, and a rapid increase in average values and in variance from 0.85–0.6 Ma to the present, indicating lowered chemical weathering intensity in both the dust source regions and the depositional areas. This event may be causally related to the expansion of northern hemisphere ice and/or the regional tectonic uplift of high mountains in Asia since the mid-Pleistocene.
-
geochemistry of the pliocene red clay formation in the chinese Loess plateau and implications for its origin source provenance and paleoclimate change
Geochimica et Cosmochimica Acta, 2001Co-Authors: Zhongli Ding, Jimin Sun, Shiling Yang, Tungsheng LiuAbstract:Abstract Recent field observations and sedimentological studies suggest the eolian origin of the late Tertiary red clay formation underlying the Pleistocene Loess-Soil sequence in the Loess Plateau, thereby extending the wind-blown record from ∼2.6 Ma down to ∼7.0 Ma in north-central China. To address the source provenance of the red clay, major and trace element concentrations were analyzed on the samples from a north-south Loess transect of the Loess Plateau and a red clay section at Jiaxian. Results show that there is a good agreement of both major and trace element compositions between the last glacial-interglacial Loess-Soil units and the Jiaxian red clay record. The REE distribution patterns of the Loess-Soil and red clay samples are remarkably similar in shape, with enriched LREE and fairly flat HREE profiles and clear negative Eu anomaly. The geochemical features of the red clay are also identical to those of upper continental crust. These chemical characteristics provide further evidence for eolian sedimentation of the red clay. From the relations both between Na2O/Al2O3 and K2O/Al2O3 ratios and between U/Pb and Th/Pb ratios, the eolian Loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area. The chemical similarity between Soil unit S1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern China during the late Tertiary. Comparison of down-section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that CaO/Al2O3, Sr/Rb and Sr/Ba are more sensitive to climate changes than magnetic susceptibility, and can be used to reconstruct the climate history of the late Cenozoic.
-
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.
-
preliminary magnetostratigraphy of a thick eolian red clay Loess sequence at lingtai the chinese Loess plateau
Geophysical Research Letters, 1998Co-Authors: Zhongli Ding, Jimin Sun, Shiling Yang, Ting LiuAbstract:Magnetic remanence and bulk susceptibility measurements are reported for a 305-m eolian Loess-red clay sequence at Lingtai, the Chinese Loess Plateau. Polarity zonation defined by about 680 remanence data yields a basal age of about 7.05 Ma for the section, which represents the oldest wind-blown dust deposited continuously in north-central China during the late Cenozoic. The resultant magnetostratigraphic scheme implies a nearly linear accumulation rate (about 2.98 cm/ka) of atmospheric dust on the Loess Plateau during the period of 7.05 to 2.58 Ma. Comparison of the bulk susceptibility record with the pedogenic characteristics of the red clay observed in the field suggests that magnetic susceptibility in the red clay is not as useful as in the Loess-Soil sequence to indicate summer monsoon variations.
Qingzhen Hao - One of the best experts on this subject based on the ideXlab platform.
-
magnetostratigraphy of an early middle miocene Loess Soil sequence in the western Loess plateau of china
Geophysical Research Letters, 2007Co-Authors: Qingzhen Hao, Zhengtang GuoAbstract:[1] Stratigraphy and magnetic susceptibility of the Quaternary eolian deposits at different sites in China can be closely correlated, confirming their spatial coherence and temporal continuity. The extent to which these conclusions are true for the Miocene Loess-Soil sequences remains to be addressed. Here, a 231.9-m eolian section, QA-III, is geomagnetically dated, yielding an age span of 21.4–11.4 Ma, with the portion older than 19.6 Ma being partially water-reworked. The magnetozones, litholigic structure and magnetic susceptibility of the sequence are highly correlative with the QA-I and QA-II sections, 30 km west of QA-III. These sequences demonstrate that the Miocene Loess deposits are also spatially correlative in stratigraphy, present a near-continuous sequence of paleoenvironment changes, and that magnetic susceptibility is a useful tool for stratigraphic correlation. The basal age of QA-III confirms again the onset of Asian inland deserts and monsoon-dominate climates by the early Miocene.
-
late miocene pliocene development of asian aridification as recorded in the red earth formation in northern china
Grid and Pervasive Computing, 2004Co-Authors: Zhengtang Guo, Qingzhen Hao, Shuzhen Peng, Pierre E Biscaye, Tungsheng LiuAbstract:In northern China, the Late Miocene–Pliocene Hipparion Red-Earth Formation in the eastern Loess Plateau fills a gap of climate records between the well-known Loess-Soil sequences of the last 2.6 Ma and the Miocene Loess-Soil sequences from the western Loess Plateau. Earlier studies on type sections indicate that a major part of the Red-Earth Formation is also of windblown origin, covering the period from f7–8 tof2.6 Ma BP. Because the eolian dust deposited in the region originated from the Asian desert lands, the Red-Earth must contain a record of the aridification history of the Asian interior. In this study, the Xifeng type section in the eastern Loess Plateau is studied to assess the development of Asian aridification during Late Miocene–Pliocene time. Eolian dust deposition continued at the central Loess Plateau since f6.2 Ma BP, indicating that sizable desert lands in the interior of Asia and the Asian winter monsoon must have been constantly maintained during Late Miocene–Pliocene time, and were able to provide a significant amount of eolian dust. The aridity in the source areas was stronger from f6.2 to f5 Ma BP and weaker from f 5t of3.6 Ma BP. Two major aridification steps are observed at f3.6 and f2.6 Ma BP, respectively. The intensification of eolian deposition at f3.6 Ma BP is synchronous with a suggested uplift of portions of the Tibetan Plateau. The general aridification history is also highly consistent with the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets during this interval. Our results therefore suggest that both Tibetan uplift and ice-building processes in the northern hemisphere were two prominent driving forces behind the long-term desertification in the interior of Asia during Late Miocene and Pliocene time. D 2004 Elsevier B.V. All rights reserved.
-
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.
-
Loess Soil sequences in southern anhui province magnetostratigraphy and paleoclimatic significance
Chinese Science Bulletin, 2003Co-Authors: Yansong Qiao, Zhengtang Guo, Qingzhen Hao, Wenying Jiang, Baoyin Yuan, Zhongshi Zhang, Jianjing Wei, Hua ZhaoAbstract:Two parallel Loess-Soil sequences from Xuancheng and Fanchang in southern Anhui Province are dated using geomagnetic and luminescence methods. The Brunhes/Matuyama (B/M) reversal boundary is recognized within the lower part of the so-called Vermiculated Red Soil (VRS) in the Xuancheng section while the entire Fanchang sequence is of Brunhes age. This indicates that the most recent VRS in southern China, a stratigraphic marker and an indication of extremely warm-humid conditions, was formed during the middle Pleistocene, chronologically correlative with the S4 and S5 Soil units in northern China. Microscopic and sedimentologic investigations reveal that eolian deposition started in this region at about 0.85 MaBP, roughly synchronous with the well-known Mid-Pleistocene climate change of global significance. The strengthening of both summer and winter monsoon circulations and the consequent river hydrological changes at that time would have provided favorable conditions for sustained eolian deposition in the middle-lower reaches of the Yangtze River since 0.85 MaBP.
Pierre E Biscaye - One of the best experts on this subject based on the ideXlab platform.
-
late miocene pliocene development of asian aridification as recorded in the red earth formation in northern china
Grid and Pervasive Computing, 2004Co-Authors: Zhengtang Guo, Qingzhen Hao, Shuzhen Peng, Pierre E Biscaye, Tungsheng LiuAbstract:In northern China, the Late Miocene–Pliocene Hipparion Red-Earth Formation in the eastern Loess Plateau fills a gap of climate records between the well-known Loess-Soil sequences of the last 2.6 Ma and the Miocene Loess-Soil sequences from the western Loess Plateau. Earlier studies on type sections indicate that a major part of the Red-Earth Formation is also of windblown origin, covering the period from f7–8 tof2.6 Ma BP. Because the eolian dust deposited in the region originated from the Asian desert lands, the Red-Earth must contain a record of the aridification history of the Asian interior. In this study, the Xifeng type section in the eastern Loess Plateau is studied to assess the development of Asian aridification during Late Miocene–Pliocene time. Eolian dust deposition continued at the central Loess Plateau since f6.2 Ma BP, indicating that sizable desert lands in the interior of Asia and the Asian winter monsoon must have been constantly maintained during Late Miocene–Pliocene time, and were able to provide a significant amount of eolian dust. The aridity in the source areas was stronger from f6.2 to f5 Ma BP and weaker from f 5t of3.6 Ma BP. Two major aridification steps are observed at f3.6 and f2.6 Ma BP, respectively. The intensification of eolian deposition at f3.6 Ma BP is synchronous with a suggested uplift of portions of the Tibetan Plateau. The general aridification history is also highly consistent with the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets during this interval. Our results therefore suggest that both Tibetan uplift and ice-building processes in the northern hemisphere were two prominent driving forces behind the long-term desertification in the interior of Asia during Late Miocene and Pliocene time. D 2004 Elsevier B.V. All rights reserved.
-
origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments
Palaeogeography Palaeoclimatology Palaeoecology, 2001Co-Authors: Shuzhen Peng, Pierre E BiscayeAbstract:Abstract In the eastern Loess Plateau region of northern China, the Quaternary Loess-Soil sequences of the last 2.6 Ma are underlain by the Hipparion Red-Earth Formation. Magneto-stratigraphic studies suggest that it is a near continuous terrestrial record for the period from ∼7 to ∼2.6 Ma BP, and therefore, has great potential for the study of Asian paleoclimates. The origin of this formation is controversial and needs further study. In this work, the Xifeng Red-Earth section, a type section for the eastern Loess Plateau region, was studied using optical microscopic analysis, grain-size measurements, and both major- and trace-element geochemical properties to address questions of its origin and environmental implications. The results show that this formation consists of three parts. The Lower part (>6.2 Ma BP) is a water-reworked deposit related to alluvial and slope processes; the Middle part (from ∼6.2 to ∼3.6 Ma BP) was derived from in situ eolian dust deposition, but was significantly affected by groundwater oscillations; and the Upper part (from ∼3.6 to ∼2.6 Ma BP) is an eolian formation, similar to the Quaternary Loess-Soil sequence. The grain-size of the Upper part is significantly coarser than for the middle part, but finer than for the overlying Loess. Because the eolian dust deposits in the middle reaches of the Yellow River were mainly transported from the deserts in northern China by the northwesterly winter monsoon wind and the westerlies, we interpret the eolian origin of the Middle and Upper Red-Earth formation, beginning approximately at 6.2 Ma BP, as an indication of the strengthening of the aridification of the Asian continent. Desert lands in Central Asia must have been formed at or by that time to provide a significant source of dust. However, the generally finer grain-size of the Red-Earth suggests a weaker transporting wind, and/or a more remote source. The latter implies a smaller extent of deserts than in the Quaternary. The high degree of similarity between the geochemical properties of the Red-Earth and Loess samples seems to suggest a rather similar source areas and comparable dust-transporting trajectories. The removal of the dust deposits from groundwater influence and the increase in grain-size at ∼3.6 Ma BP are attributable to both tectonic and climatic causes. The initiation of these phenomena corresponds to an intensive uplift of the Tibetan Plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas. It is also approximately synchronous with an increase in eolian mass accumulation rate in the North Pacific, both suggesting an increased continental aridity in the Asian dry lands, and an increasing intensity of transporting winds.
-
summer monsoon variations over the last 1 2 ma from the weathering of Loess Soil sequences in china
Geophysical Research Letters, 2000Co-Authors: Zhengtang Guo, Shuzhen Peng, Pierre E Biscaye, Lanying Wei, Xihui Chen, Tungsheng LiuAbstract:The Loess-Soil sequence in northern China contains a near continuous record of Quaternary paleoclimate. Magnetic susceptibility and grain size have so far been the only proxies available to address the long-term changes of the East-Asian paleomonsoon extending back to more than one million years. In this study, the ratio of CBD (citrate-bicarbonate-dithionite)-extractable free Fe2O3 (FeD), a measure of iron liberated by chemical weathering, versus the total Fe2O3 available (FeT) was measured on samples at 10 cm intervals taken from two Loess sections deposited over the last 1.2 Ma. Variations of this index are highly consistent with other pedological indicators, but in addition provide a quantitative measurement of the degree of pedogenesis in the Loess Plateau. Since chemical weathering in the region mainly depends upon summer precipitation and temperature, weathering intensity primarily reflects changes in the East-Asian summer monsoon. The new proxy has been used to document a series of summer monsoon changes of global significance, which are not necessarily recorded by magnetic susceptibility.
