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Paleomagnetic and mineral magnetic investigation of the Baicaoyuan loess-paleosol sequence of the western Chinese Loess Plateau over the last glacial-interglacial cycle and its geological implications

Paleomagnetic and mineral magnetic investigation of the Baic...

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中国科学院地质与地球物理研究所2008学术年会

作者： Chenglong Deng Paleomagnetism and Geochronology Laboratory(SKL-LE),Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box 9825,19 Beituchengxi Road,Beijing 100029,China

[1]Closely spaced paleomagnetic and mineral magnetic studies were conducted on the Baicaoyuan(BCY) loess-paleosol sequence since the last interglacial in the western Chinese Loess *** multiproxy records of mineral magnetic parameters clearly indicate loess-paleosol alternations with the fine structure of pedostratigraphy over the last glacial-interglacial ***,the paleomagnetic results reveal the absence of any short-lived geomagnetic excursions in the BCY *** absence could be interpreted by two alternative mechanisms,such as magnetic overprinting and discontinuous *** absence of the Mono Lake and Laschamp excursions in the loess unit L1 is probably due to the viscous overprinting of the remanence carried by coarse-grained magnetite of eolian origin and/or to the episodic nature of loess accumulation during the last glacial ***,discontinuous sediment accumulation may more probably lead to the absence of the Blake excursion in the last interglacial soil S1 as well as of the Mono Lake and Laschamp excursions in the last glacial loess L1 at the BCY *** with previously published paleomagnetic results from other sections over the Loess Plateau,the findings probably further indicate the discontinuous nature of loess accumulation in the western Loess Plateau, where sedimentation of the last interglacial soil may be episodic at the timescale equivalent to the duration of the Blake geomagnetic excursion(4-6 ka),much longer than the timescale for episodic loess sedimentation in the last glacial loess of both the western and eastern Loess Plateau due to the reduced sediment accumulation rate compared to that during the last glacial ***,sediments with relatively high sedimentation rate in some parts of the western Loess Plateau do not consistently guarantee the faithful recording of high-frequency geomagnetic variations.

关键词： Chinese loess paleomagnetism mineral magnetism magnetic overprinting episodic loess accumulation last glacial-interglacial cycle

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Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau

Paleoclimatic significance of mineral magnetic properties of...

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中国科学院地质与地球物理研究所2003学术年会

作者： WANG Xiaoyong~1,LU Huayu~1,LI Zhen~2, DENG Chenglong~3,TAN Hongbing~4 & SONG Yougui~1 1.State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710075, China 2.Department of Geography,Qinghai Normal University,Xining 810008, China 3.Paleomagnetism Laboratory,Institute of Geology and Geophysics, Chinese Academy of Sciences,Beijing 100029,China 4.Institute of Saline Lake,Chinese Academy of Sciences,Xining 810008,China

Loess deposit in the northeastern Qing-hai -Tibetan Plateau offers an excellent record of climate and environment changes in this *** have conducted multiparameter mineral magnetic analyses of samples of loess deposits from the Dongchuan,Lalakou and Panzishan sections. The methods used include magnetic susceptibility,frequency -dependent susceptibility,temperature-dependent susceptibility,isothermal remanent magnetization acquisition, and magnetic hysteresis *** results reveal that magnetite is the dominant contributor to magnetic susceptibility. Maghemite and hematite is also present in the loess layers and paleosol *** higher concentration of maghemite in paleosols suggests that the formation of maghemite occurred during in situ pedogenesis,which plays an important role in the enhancement of the magnetic susceptibility. Similar to that in the Chinese Loess Plateau lying to the east of the Liupan Mountains,magnetic granulometry in the studied loess and paleosols is predominantly pseudo-single-domain(PSD).However,the mean grain-size of the ferrimagnetic minerals in loess is evidently coarser (larger PSD and multidomain-like) than in paleosols(mainly PSD).The magnetic susceptibility of loess and paleosols is positively correlated with the content of ultrafine magnetite /maghemite grains,and hence with the intensity of in situ ***,the enhanced magnetic susceptibility in the studied loess-paleosol sequences can be interpreted as being due to climatically induced in situ pedogenesis.

关键词： mineral magnetism loess-paleosol Qinghai-Tibetan Plateau magnetic susceptibility

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mineral magnetic properties of loess/paleosol couplets of the central loess plateau of China over the last 1.2 Myr

Mineral magnetic properties of loess/paleosol couplets of th...

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中国科学院地质与地球物理研究所2004学术年会

作者： Kenneth L.Verosub Michael J.Singer Natasa J.Vidic Department of Geology University of CaliforniaDavis.CaliforniaUSA Department of Land Air and Water ResourcesUniversity of CaliforniaDavisCaliforniaUSA Department of Geology University of CaliforniaDavisCaliforniaUSA Agronomy Department University of LjubljanaLjubljanaSlovenia

[1]We have conducted a multiparameter investigation of 15 loess-paleosol couplets (S0/L1 to S14/L15) from the Jiaodao section in the central loess plateau of China using environmental magnetic approaches coupled with soil science *** magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of ***-temperature susceptibility curves of palcosols show a generally decreasing trend in reversibility from the base of the Lishi Formation to the Holocene black loam,possibly indicating a decrease in weathering *** may reflect a long-term increase in aridity and/or a general long-term cooling trend of the interior of the Asian continent from 1.2 Ma to the *** samples display wasp-waisted hysteresis *** are most pronounced in moderately enhanced paleosols,less pronounced in the practically unaltered loess,and subdued in the well-developed paleosols,but wasp waistedness reappears in the most developed *** wasp-waistedness sequence suggests that the composition,concentration,and grain size of magnetic minerals all contribute to the hysteresis behavior of samples from the studied loess-paleosol sequence,but each factor has a different effect at different stages of *** TERMS: 1540 Geomagnetism and Paleomagnetism:Rock and mineral magnetism;1512 Geomagnetism and Paleomagnetism:Environmental magnetism;1519 Geomagnetism and Paleomagnetism:Magnetic mineralogy and petrology

关键词： loess paleosol mineral magnetism pedogenesis loess plateau

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mineral magnetic variation of the Jingbian loess/paleosol sequence in the northern Loess Plateau of China:Implications for Quaternary development of Asian aridification and cooling

Mineral magnetic variation of the Jingbian loess/paleosol se...

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中国科学院地质与地球物理研究所2006学术年会

作者： John Shaw Geomagnetism Laboratory Department of Earth and Ocean SciencesUniversity of LiverpoolLiverpool L69 7ZEUK

A high-resolution mineral magnetic investigation has been carried out on the Jingbian loess/paleosol sequence at the northern extremity of the Chinese Loess *** show that the magnetic assemblage is dominated by large pseudo-single domain and multidomain-like magnetite with associated maghemite and *** in the ratios of SIRMT/SIRM, SIRM/SIRM and SIRM/SIRM(SIRM is the saturation isothermal remanent magnetization;SIRM represents the residual SIRM after an n mT alternating field demagnetization) have been used to document regional paieoclimate change in the Asian interior by correlating the mineral magnetic record with the compositeδO record in deep-sea sediments. The long-term up-section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long-term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema,respectively,which reveals a long-term decreasing trend in chemical weathering intensity in both glacial-stage source region (the Gobi and deserts in northwestern China) and interglacial-stage depositional area(the Loess Plateau region).We further relate this long-timescale variation to long-term increasing aridification and cooling,during both glacial extrema in the dust source region and interglacial extrema in the depositional area,over the Quaternary *** in those ratios are most likely due to Quaternary aridification and cooling driven by ongoing global cooling,expansion of the Arctic ice-sheet,and progressive uplift of the Himalayan-Tibetan complex during this period.

关键词： Chinese Loess Plateau loess paleosol mineral magnetism magnetoclimatology Asian aridification and cooling

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mineral-magnetic signal of long-term climatic variation in Pleistocene fluvio-lacustrine sediments,Nihewan Basin(North China)

Mineral-magnetic signal of long-term climatic variation in P...

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中国科学院地质与地球物理研究所第十届(2010年度)学术年会

作者： Hong Ao Paleomagnetism and Geochronology Laboratory(SKL-LE),Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xian 710075,China Graduate University of Chinese Academy of Sciences,Beijing 100049,China

The Nihewan Basin(around 40°N,North China)is a major focus of investigations into hominid occupation in the eastern Asia during the early Pleistocene,thus the paleoenvironmental evolution in this area is crucial for understanding of early human habitation at high northern latitudes of East *** retrieve reliable long-term paleoenvironmental signals from the Nihewan fluvio-lacustrine sequences,I conduct an environmental magnetic investigation on the Pleistocene Xiantai fluvio-lacustrine sequence at the eastern margin of the Nihewan *** suggest that there exist an up-section decreasing trend in magnetic mineral concentration and grain size,which is attributed to a long-term decrease in abundance of magnetic minerals in the catchments and in transportation of detrital magnetic minerals into the Nihewan paleolake.I further reveal that these long-timescale variations are related to a long-term decrease in East Asian monsoon precipitation and humidity in the Nihewan Basin during the *** paleoclimate inference is consistent with the increasing aridification in Asian mainland during the Pleistocene, an important climate response to increasing global ice volume.

关键词： Environmental magnetism mineral magnetism Nihewan Basin Pleistocene Fluvio-lacustrine sediment

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