Mineralogic and Climatic Interpretations of the Luochuan Loess Section (China) Based on Diffuse Reflectance Spectrophotometry

2001 ◽  
Vol 56 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Junfeng Ji ◽  
William Balsam ◽  
Jun Chen
Keyword(s):  
Magnetic Susceptibility ◽  
Summer Monsoon ◽  
Diffuse Reflectance ◽  
Near Infrared ◽  
Relative Proportion ◽  
Chinese Loess Plateau ◽  
Early Pleistocene ◽  
Chinese Loess ◽  
Near Ultraviolet ◽  
Reflectance Data

AbstractWe examined the top 135 m, that is, the entire Pleistocene, of the classic Luochuan section on the Chinese Loess Plateau with a diffuse reflectance spectrophotometer from the near ultraviolet, through the visible, and into the near infrared. From the reflectance data we calculated sample brightness which, with some caveats, is a reasonable proxy for magnetic susceptibility. Mineralogic changes were identified by factor analyzing the first derivative of the percent reflectance data and examining samples with high factor scores. Two factors which explain about 96% of the cumulative variance are distinguished by the relative proportion of hematite and goethite, the minerals that are responsible for the color changes in the loess sequence. Both hematite and goethite are present in both loess and paleosol but goethite dominates in loess whereas hematite dominates in paleosol. The goethite factor exhibits an inverse correlation with magnetic susceptibility; the hematite factor exhibits a weak positive correlation with susceptibility. Paleoclimatic interpretations are drawn from comparison of susceptibility to the concentration of spectrally identified hematite. Based on this comparison, paleosols in the early Pleistocene Wucheng Formation are characterized by conditions that are drier than today, a “dry summer monsoon”, whereas later Pleistocene paleosols are characterized by a “wet summer monsoon”.

Magnetic susceptibility evidence of monsoon variation on the Loess Plateau of central China during the last 130,000 years

1991 ◽  
Vol 36 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Zhisheng An ◽  
George J. Kukla ◽  
Stephen C. Porter ◽  
Jule Xiao
Keyword(s):  
Magnetic Susceptibility ◽  
Loess Plateau ◽  
Summer Monsoon ◽  
Central China ◽  
Chinese Loess Plateau ◽  
Climate Index ◽  
Chinese Loess ◽  
Monsoon Variability ◽  
Monsoon Intensity ◽  
Isotope Record

AbstractThe magnetic susceptibility of loess and paleosols in central China represents a proxy climate index closely related to past changes of precipitation and vegetation, and thus to summer monsoon intensity. Time series of magnetic susceptibility constructed for three loess-paleosol sequences in the southern part of the Chinese Loess Plateau document the history of summer monsoon variation during the last 130,000 yr. They correlate closely with the oxygen isotope record of stages 1 to 5 in deep-sea sediments. Soils were forming during intervals of strong summer monsoon, whereas loess units were deposited at times of reduced monsoon intensity. The Chinese loess-paleosol sequence can thus be viewed as a proxy record of Asian monsoon variability extending over the last 2.5 myr.

scholarly journals Palaeoclimatic changes in northeastern Qinghai-Tibetan Plateau revealed by magnetostratigraphy and magnetic susceptibility analysis of thick loess deposits

2012 ◽  
Vol 91 (1-2) ◽  
pp. 189-198 ◽  
Author(s):  
H.Y. Lu ◽  
Xianyan Wang ◽  
Xiaoyong Wang ◽  
X.F. Sun ◽  
S.W. Yi ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Luminescence Dating ◽  
Chinese Loess Plateau ◽  
Surface Erosion ◽  
Chinese Loess ◽  
Extensive Surface ◽  
Loess Deposits ◽  
Good Proxy

AbstractReconstruction of a complete Quaternary record of climatic changes in the northeastern Qinghai-Tibetan Plateau is not well obtained, because of high relief and extensive surface erosion. In this study, two long cores obtained from thick loess deposits in the region, both contain clear alternations of loess and paleosols, indicating distinct climate changes during the Quaternary. The palaeomagnetic stratigraphy and optically stimulated luminescence dating indicate that the loess deposition began approximately 2.0 Ma ago, with continuous accumulation until the Holocene. Dust accumulation rates in this region are much higher than those in the central Chinese Loess Plateau, suggesting an extended dust source and/or robust transport agent. Variations of magnetic susceptibility of the loess are a good proxy index of warm/wet and cold/dry alternations and are correlated with the intensity of pedogensis. The magnetic susceptibility record reveals that a relatively cold/dry climate dominated the northeastern Qinghai-Tibetan Plateau in the Quaternary, punctuated by warm/wet phases. A stepwise strengthening of the plateau summer monsoon, with a significant strengthening at around 1200-1000 ka and at least 7 phases of strengthening of the plateau summer monsoon in the past 800 ka are interpreted from the core data. The cores provide evidence that strengthened warm/wet climates occurred at around 80-130, 190-250, 290-340, 385-420, 500-625, 690-720 and 755-780 ka, which may correlate to warm/wet phases in the Qinghai-Tibetan Plateau. The palaeoclimate changes probably were regulated by the glacial-interglacial alternations.

Reconsidering the paleoclimate implications of magnetic susceptibility records of Holocene loessic soils

2021 ◽  
Author(s):  
Diana Jordanova ◽  
Neli Jordanova
Keyword(s):  
Magnetic Susceptibility ◽  
Parent Material ◽  
Chinese Loess Plateau ◽  
Absolute Difference ◽  
Physical Parameters ◽  
Soil Profiles ◽  
Chinese Loess ◽  
Loess Area ◽  
River Terraces ◽  
Paleoclimate Proxy

<p>Mass specific magnetic susceptibility variations with depth along soil profiles developed on loess parent material is one of the most frequently used physical parameters in local, regional and global correlations of loess deposits. It is also utilized as a paleo-precipitation proxy, defined either as absolute difference between susceptibilities of the enhanced B-horizon and parent loess, or as relative enhancement using ratios of magnetic parameters. These different approaches in the application of magnetic susceptibility as paleoclimate proxy lead us to perform a comparative study on a number of Holocene soil profiles developed on loess from European loess area and the Chinese Loess Plateau (CLP). We made a compilation of data including 20 profiles from North Bulgaria, 28 profiles from Eastern and Central Europe; and 26 profiles from the CLP. Minimum magnetic susceptibilities of the last glacial loess (X<sub>min</sub>) from the compiled data base for European and Chinese profiles show climate related variability, revealing multi linear relationship with both present day MAP and MAT values for the corresponding locations. Strong deviations of X<sub>min</sub> from this dependence display sites located at low elevation river terraces, Black sea coast and possessing large content of coarse silt and sand fractions. Pedogenic magnetic susceptibility (X<sub>pedo</sub>) defined as (X<sub>max</sub> - X<sub>min</sub>) with  X<sub>max</sub> determined from the youngest part (last 1500 – 2000 years B.P.) of the Holocene magnetic susceptibility records of Chinese sections and absolute X<sub>max</sub> of the European sites show systematic dependence on modern MAP and MAT values. This dependence is uniform for all sites with steppe vegetation, while higher scatter and steeper regression trends are observed for sites under mixed (steppe – forest) and forest vegetation. The study is financially supported by project No KP-06-N34/2 funded by the Bulgarian National Science Fund.</p>

scholarly journals Centennial- to millennial-scale monsoon changes since the last deglaciation linked to solar activities and North Atlantic cooling

2020 ◽  
Vol 16 (1) ◽  
pp. 315-324 ◽  
Author(s):  
Xingxing Liu ◽  
Youbin Sun ◽  
Jef Vandenberghe ◽  
Peng Cheng ◽  
Xu Zhang ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
North Atlantic ◽  
Chemical Weathering ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Chinese Loess Plateau ◽  
Last Deglaciation ◽  
Chinese Loess ◽  
The Last Deglaciation

Abstract. Rapid monsoon changes since the last deglaciation remain poorly constrained due to the scarcity of geological archives. Here we present a high-resolution scanning X-ray fluorescence (XRF) analysis of a 13.5 m terrace succession on the western Chinese Loess Plateau (CLP) to infer rapid monsoon changes since the last deglaciation. Our results indicate that Rb∕Sr and Zr∕Rb are sensitive indicators of chemical weathering and wind sorting, respectively, which are further linked to the strength of the East Asian summer monsoon (EASM) and the East Asian winter monsoon (EAWM). During the last deglaciation, two cold intervals of the Heinrich event 1 and Younger Dryas were characterized by intensified winter monsoon and weakened summer monsoon. The EAWM gradually weakened at the beginning of the Holocene, while the EASM remained steady till 9.9 ka and then grew stronger. Both the EASM and EAWM intensities were relatively weak during the Middle Holocene, indicating a mid-Holocene climatic optimum. Rb∕Sr and Zr∕Rb exhibit an antiphase relationship between the summer and winter monsoon changes on a centennial timescale during 16–1 ka. Comparison of these monsoon changes with solar activity and North Atlantic cooling events reveals that both factors can lead to abrupt changes on a centennial timescale in the Early Holocene. During the Late Holocene, North Atlantic cooling became the major forcing of centennial monsoon events.

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