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ZHANG HuCai CHANG FengQin LI Bin LEI GuoLiang CHEN Yue ZHANG WenXiang NIU Jie FAN HongFang YANG MingSheng 《科学通报(英文版)》2007,52(9):1248-1256
Blomarkers of paleolake deposits from Qarhan Salt Lake in Qaidam Basin, northwest China were systematically analyzed and the A--C series compounds of branched aliphaUc alkanes with quaternary substituted carbon atom (BAQCs) were identified. The homologous distinguished three series, A-C, were identified as 5,5-diethylalkanes, 6,6-diethylalkanes and 5-butyl, 5-ethylalkanes series, and their relative abundance was A 〉 B 〉 C. Series A and C were characterized by odd carbon numbers, whereas series B was characterized by even carbon numbers. The high values of series A corresponded with the high values of series B and C. Therefore, it can be concluded that series A, B and C possess a similar biological origin. The abundance of series A was relatively low in the lower part of the section compared with that in the upper part, implying that these series originated from bacteria and/or algae more prevalent in fresh-mesohaline water, and such kinds of bacteria and/or algae are most likely to be thermophilous species. The A25/nC25 ratio differences in the section show that such branched aliphatic alkanes can be treated as one kind of environmental change proxy for paleolake evolution and may provide important information for the climate reconstruction of the Late Pleistocene. 相似文献
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NACE Trevor 《科学通报(英文版)》2011,56(14):1503-1510
Gas chromatography-mass spectrometry was used to identify a series of n-alkanes in the sediments of a typical glacially eroded lake in the eastern Tibetan Plateau.By comparing the distribution patterns of n-alkanes in lake sediments,surface soils and cow manure,it was shown that n-C 27-n-C 33 alkanes in the soil ecosystem of Ximen Co are derived from vascular plant species and that the distribution pattern of n-C 27-n-C 33 alkanes remains unchanged during the feeding and digestion processes of herbivores.The relative percentage of C 27,C 29 and C 31 n-alkanes decreased from the bottom to the top of the sediment core showing a trend of degradation of higher plants in the Ximen Co lake region during the formation of the 44 cm core.210 Pb dating,combined with pre-existing AMS 14 C dating results showed that the depositional core reflects climatic and environmental variations since about 900 years before present.The n-alkane indexes (ACL 27-33,P aq,P wax) are comparable with regional temperature variation,especially recording the Little Ice Age event (LIA).This study highlights that n-alkanes are valid proxies for paleo-climate and paleo-environment reconstruction,despite the same distribution patterns in n-alkane molecular fossils derived from a typical glacially eroded lake. 相似文献
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Lü YanWu Gu ZhaoYan Aldahan Ala Zhang HuCai Possnert Göran Lei GuoLiang 《科学通报(英文版)》2010,55(33):3802-3809
Reconstructing the evolutionary history of the Gobi deserts developed from alluvial sediments in arid regions has great significance
in unraveling changes in both tectonic activity and climate. However, such work is limited by a lack of suitable dating material
preserved in the Gobi Desert, but cosmogenic 10Be has great potential to date the Gobi deserts. In the present study, 10Be in quartz gravel from the Gobi deserts of the Ejina Basin in Inner Mongolia of China has been measured to assess exposure
ages. Results show that the Gobi Desert in the northern margin of the basin developed 420 ka ago, whereas the Gobi Desert
that developed from alluvial plains in the Heihe River drainage basin came about during the last 190 ka. The latter developed
gradually northward and eastward to modern terminal lakes of the river. These temporal and spatial variations in the Gobi
deserts are a consequence of alluvial processes influenced by Tibetan Plateau uplift and tectonic activities within the Ejina
Basin. Possible episodes of Gobi Desert development within the last 420 ka indicate that the advance/retreat of alpine glaciers
during glacial/interglacial cycles might have been the dominant factor to influencing the alluvial intensity and water volume
in the basin. Intense floods and large water volumes would mainly occur during the short deglacial periods. 相似文献
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