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Peng T.,Lanzhou University | Li J.,Lanzhou University | Li J.,Nanjing Normal University | Song C.,Key Laboratory of Western Chinas Environmental Systems | And 4 more authors.
Geophysical Research Letters

Fine-grained Miocene sediments from Tianshui Basin, northeastern Tibetan Plateau, have received intense attention recently because these sediments were identified as loess. The presence of early Miocene loess pushes the timing of initiation of inland Asian desertification from 8 Ma back to 22 Ma. However, mudflat/distal fan and shallow lake sediments of Miocene have also been reported in Tianshui Basin. Consequently, the origin of these fine-grained Miocene sediments in this area remains controversial. Here we investigate the n-alkane biomarker characteristics of Neogene sediments from a north-south transect of exposures within Tianshui Basin and compare these molecular distributions with those published Quaternary loess to help resolve the disputed origin. We found that n-C23 and n-C25 alkanes, sourced from either aquatic macrophytes or palustrine plants, are ubiquitous in the Miocene sediments from Tianshui Basin but are largely absent in Quaternary loess. This striking difference between n-alkane distributions in the Tianshui samples and the Quaternary loess casts doubt on an eolian origin for the Tianshui samples and challenges the hypothesis of an early Miocene onset of Asian interior desertification. Copyright 2012 by the American Geophysical Union. Source

Wang X.,Lanzhou University | Nan Z.,Lanzhou University | Ding W.,Key Laboratory of Western Chinas Environmental Systems | Wang S.,Lanzhou University | And 3 more authors.
Arid Land Research and Management

Heavy metals in soil arising from mining and wastewater irrigation have greatly threatened human health and the environment. This research used pot experiments to study the fraction and bioavailability of Cd, Pb, Zn, and Ni in irrigated desert soil from oasis regions of Northwest China. The accumulation of selected heavy metals in the tissues of cole crops (Brassica campestris L.) was studied, and the bioavailability of selected metals in soils to cole crops was analyzed by Pearson coefficients. The results show different levels of accumulation of the selected heavy metals in cole crop tissues, which are shown as follows: leaves have a higher content of Cd than roots; roots have a higher content of Pb and Ni than leaves; the contents of Zn in leaves and roots are almost the same. Cd and Zn mainly accumulate in the edible part of the cole crop in arid soil. The exchangeable fraction of Cd, Pb, Zn, and Ni, the carbonate bound fraction of Zn and Ni, were available to the cole crop. Health risk index values for selected heavy metals were less than 1 for both control soil and spiked soils in case of Cd in treatment No. 8. Cole crops grown on spiked soil can pose health risks because of a high concentration of Cd. © 2012 Copyright Taylor and Francis Group, LLC. Source

Zhao Y.,CAS Institute of Tibetan Plateau Research | Zhao Y.,University of Chinese Academy of Sciences | Wu F.,CAS Institute of Tibetan Plateau Research | Wu F.,Chinese Academy of Sciences | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology

Sediment carbon/nitrogen (C/N) ratios can play an important role in reconstructing lacustrine and coastal paleo-environments, because significantly different C/N ratios result from aquatic phytoplankton versus organic matter derived from terrestrial plants. However, researchers have not yet taken into account the fact that topsoil organic matter is another important terrestrial organic source for lacustrine and coastal sediments. A study of topsoil C/N ratios from the Heihe and Shiyang River drainage basins, located in the Qilian Mountains on the northeast margins of the Tibetan Plateau, shows that topsoil C/N ratios can be as low as those of subaqueous sediments. 80.4% of total topsoils in the Heihe River drainage basin, and 67.7% of total topsoils in the Shiyang River drainage basin, have C/N ratios below 12, while 18.8% of all samples in the Heihe river drainage basin, and 29.2% of all samples in the Shiyang river drainage basin, possess C/N ratios between 12 and 20. Traditionally, researchers have considered that low C/N ratios indicate subaqueous deposition; however, these sediments are terrestrial and most of the organic matter is derived from land plants. Furthermore, topsoil C/N ratios from both the Heihe and Shiyang river drainage basins correlate significantly with altitude and local vegetation. Our results indicate that not all C/N ratios of terrestrial organic matter (including plants and soil organic matter) equal 20 or more. Nor can one distinguish subaqueous sediment organic sources solely on the basis of C/N ratios; low subaqueous sediment C/N ratios may not simply result from a greater proportion of aquatic plants versus terrestrial organic matter, but also from low end-member terrestrial organic matter C/N ratios which are lowered by the addition of soil organic matter with its own low C/N ratios. © 2015 Elsevier B.V. Source

Song Y.,CAS Institute of Earth Environment | Song Y.,Key Laboratory of Western Chinas Environmental Systems | Fang X.,Key Laboratory of Western Chinas Environmental Systems | Fang X.,CAS Institute of Tibetan Plateau Research | And 4 more authors.
Quaternary Research (United States)

A high-resolution rock magnetic investigation was performed on the Chaona Quaternary loess/paleosol sequences in the Central Chinese Loess Plateau. Based on a newly developed independent unturned time scale and magnetic records, we reconstructed the history of the East Asia monsoons during the last 3. Ma and explored the middle Pleistocene climate transition (MPT). Rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity, lower magnetic susceptibility (MS), and that the paleosol layers are characterized by relatively high MS, saturation magnetization and remanent saturation magnetization. Spectrum analyses indicate that there are various periods in addition to orbital periodicities. According to the onset and stable appearance of 100 kyr period, we consider that the MPT recorded in this section began at ~. 1.26. Ma and was completed by ~. 0.53. Ma, which differs from previous investigations based on orbitally tuned time scales. The forcing mechanism for the MPT was more complicated than just the orbital forcing. We conclude that the rapid uplift of the Tibetan Plateau may have played an important role in the shift of periodicities during the middle Pleistocene. © 2013 University of Washington. Source

Yan Z.-X.,Key Laboratory of Western Chinas Environmental Systems | Yan Z.-X.,Lanzhou University | Ye Z.-H.,Key Laboratory of Western Chinas Environmental Systems | Ye Z.-H.,Lanzhou University | And 4 more authors.
Zhendong yu Chongji/Journal of Vibration and Shock

Stress models of the remained supporting segment of a high reinforced concrete chimney in blasting demolition was established based on dynamics principle. The regulation and the governing factors of the variation of neutral axis of cutting faces were analysed. The punching factor was used to consider the influence of sudden load. Adopting the node-split reinforced concrete model, the collapse process was numerically simulated by means of ANSYS/LS-DYNA. Through the analysis of the stress-time curve of reinforced concrete element, it is indicated that a node-split model can reflect the difference of the mechanical properties between materials of steel and concrete. Source

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