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Geochemical characterization of major elements in desert sediments and implications for the Chinese loess source

Science China Earth Sciences 2019年第9期62卷 1428-1440页

作者： Wancang ZHAO Lianwen LIU Jun CHEN junfeng ji Chongqing Key Laboratory of Karst Environment School of Geographical Sciences Southwest University Chongqing 400715 China Ministry of Education Key Laboratory of Surficial Geochemistry School of Earth Sciences and Engineering Nanjing University Nanjing 210023 China

Mineral dust released from the desert is one of the important components of atmospheric aerosols. Arid and semi-arid deserts, sandy lands in northern China and their adjacent Gobi Desert lands in northern China and neighboring Mongolia(hereinafter referred to as Gobi) are potential sources of mineral dust in Asia. However, there is currently a lack of systematic studies on the characteristics of major elements in the potential mineral dust source area. This study investigates the major elements of 310 surficial sand samples in the stabilized and semi-stabilized dune fields from 12 deserts/sandy land and Gobi in northern China and southern Mongolian Gobi and compiles published data. We identify four regions with distinct geochemical characteristics:(1) Taklimakan, Kumtag and Qaidam deserts in western China;(2) Badain Jaran, Tengger, Hobq, and Mu Us deserts in the central and western regions of northern China;(3) Hulun Buir, Onqin Daga and Horqin sandy lands in northeast China;and(4) Gobi and Gurbantunggut deserts. The spatial distributions of the SiO2 and CaO contents in Chinese deserts are highly variable. The average content of SiO2 generally reflects an increasing trend from west to east, while the average content of CaO shows a decreasing trend from west to east. We demonstrate that the spatial variation of major elements is likely controlled by two key scenarios: the composition of source rocks and the mineral maturity caused by the supply of fresh materials. The SiO2/(Al2O3+K2O+Na2O) ratio of desert sediments is relatively lower in western China and may be caused by high ferricmagnesia and high carbonate minerals;this ratio is relatively higher in the northeast sandy lands and may be linked to a lack of fresh material supply and the presence of high K-feldspar minerals in source rocks. The deserts can be further distinguished by ternary diagrams with SiO2/10-CaO-Al2O3,(K2O+Na2O)-CaO-Fe2O3 and CaO-Na2O-K2O. The comparison of major elements between desert sedimen

关键词： Desert Loess Major elements Eolian Dust Carbonate

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An EXAFS investigation of the mechanism of competitive sorption between Co(Ⅱ) and Ni(Ⅱ) at γ-alumina/solution interface

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Acta Geochimica 2017年第3期36卷 462-464页

作者： Wenxian Gou junfeng ji Wei Li Key Laboratory of Surficial Geochemistry Ministry of Education School of Earth Sciences and Engineering Nanjing University Nanjing 210023 China

Co(Ⅱ)and Ni(Ⅱ)are two common toxic heavy metals,and may simultaneously exist in contaminated water,soil,and sediment systems in Earth’s surface *** this circumstance,competitive adsorption between the two metals may influence their migration,toxicity,and *** this research,the competitive sorption of Co(Ⅱ)and Ni(Ⅱ)on γ-Al_2O_3was studied using both macroscopic sorption experiments and extended X-ray absorption fine structure(EXAFS)*** suggest that Ni(Ⅱ)reduced the amount of Co(Ⅱ)sorption in a binary-solute system at pH *** is because both Co(Ⅱ)and Ni(Ⅱ)form inner-sphere surface complexes during sorption on γ-Al_2O_3and compete for the surface reactive ***,Co(Ⅱ)exhibited a negligible influence on sorption amount of Ni(Ⅱ)under the same conditions,which suggests Ni(Ⅱ)has a stronger affinity to alumina *** pH 7.5,Co(Ⅱ)and Ni(Ⅱ)sorption density were much higher than that at pH 6.0,but there no mutual competitive effect was *** analysis further revealed that formation of layered double-hydrated precipitates was the dominant sorption mechanism for both Co(Ⅱ)and Ni(Ⅱ)at pH *** this type of sorption does not rely on surface reactive sites,there was no competition between Co(Ⅱ)and Ni(Ⅱ).This finding sheds light on risk assessment and remediation of Ni/Co pollution.

关键词： Co(Ⅱ) Ni(Ⅱ) γ-Al2O3 Competitive sorption EXAFS

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Origin of illites in the Luochuan loess section——Evidence from TEM study

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Chinese Science Bulletin 1999年第4期44卷 372-375页

作者： junfeng ji Jun Chen Huayue Lu Nanjing Univ Dept Earth Sci State Key Lab Mineral Deposit Res Nanjing 210093 Peoples R China Chinese Acad Sci Xian Lab Loess & Quaternary Geol Xian 710061 Peoples R China

Morphology and composition of illite from the Luochuan loess section were investigated by TEM. The results show that most of the illite grains are characterized by rounded shapes and chemical compositions are closely similar to those of anchizonal illites. The enrichment of illites in paleosol over loess was mainly caused by the weak winter monsoon during the interglacial periods, and was not related to the in situ pedogenesis. Illite can serve as an indicator for tracing eolian dust from Loess Plateau in pelagic and lacustrine sediments.

关键词： loess illite origin.

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Paleosandstorm characteristics and lake evolution history deduced from investigation on lacustrine sediments——The case of Hongjiannao Lake, Shaanxi Province

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Chinese Science Bulletin 2005年第20期50卷 2355-2361页

作者： SHEN ji WANG Yong YANG Xiangdong ZHANG Enlou YANG Bao ji junfeng Nanjing Institute of Geography and Limnology Chinese Academy of Sciences Nanjing 210008 China Graduate School Chinese Academy of Sciences Beijing 100039 China Key Laboratory of Ice and Cold Region Environment Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Lanzhou 730000 China Institute of Surfacial Geochemistry State Laboratory of Mineral Deposits Research Department of Earth Sciences. Nanjing University Nanjing 210009 China

Sediment cores from desert lakes serve as good records of the frequency and intensity of sandstorms in his- tory. By multi-proxy analysis of grain-size, magnetic suscep- tibility, TOC and Rb/Sr ratio, the paleosandstorm character- istics and lake evolution history in Yulin Area for the past 80 years. are discussed in this article. It is revealed that Hong- jiannao Lake formed in about 1928 A.D. and in its initial stage sandstorms were prevalent with three extremes taking place in 1936 A.D., 1939 A.D. and 1941 A.D.. During the ex- pansion period of 1952―1960 A.D., inflow waters to the lake increased sharply and a lot more weathered materials were carried into the lake. The frequency and intensity of sand- storms have reduced a lot since 1960s and the “double peaks” feature of the grain-size frequency curve has changed into the “single peak” feature. Study on the catchment ecol- ogy of the lake shows that the occurrence of sandstorms has been effectively restrained by the forest plantation and water and soil conservation.

关键词：陕西省湖泊沉积物沙暴磁化系数进化历史

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Alkylammonium cations treating and K-Ar dating of illite from mudstones

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Chinese Science Bulletin 2002年第19期47卷 1669-1672页

作者： YANG Zhongfang ji junfeng CHE Chen ZHOU Fengying China University of Geosciences Beijing 100083China State Key Laboratory of Mineral Deposit Research Institute of Surfacial GeochemistryDepartment of Earth SciencesNanjing UniversityNanjing 210093China Deposit Institute of Chinese Academy of Geological Sciences Beijing 100037China

Two kinds of mudstones from the Tarim Basin and the Tuna Basin were treated with C8 and C18 alkylammonium cations. Both of them were dated by the K-Ar method. One kind of rock contains mainly diagenetic illite, and the other contains mixed layer illite/smectite (I/S). Sample separation and alkylamnionium cations treatment were performed first, and K-Ar dating followed. The result shows that fine-grained minerals have younger K-Ar ages and coarse-grained components have older ages. Plots of K-Ar age versus K2O (%) are linear, the range of diagenetic age can be estimated by extrapolation. The reaction results of the above samples are different after alkylamnionium cations treatments. The samples containing mainly illite show a decrease in K2O and an increase in age by 1-25 Ma, suggesting that preferential exchange of young diagenetic clay rather than detrital clay by alkylamnionium cations, therefore the age of diagenetic illite can be calculated directly by the % K2O and radiogenic 40Ar removed. For the

关键词： alkylammonium cations illite K/Ar date mudstone.

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Evolution of kaolinite subgroup minerals and mixed-layer illite/smectite in the Paleogene Damintun Depression in Liaohe Basin of China and its implication for paleotemperature

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Science China Earth Sciences 2011年第1期54卷 73-83页

作者： ZHAO Ming ji junfeng CHEN ZhenYan CHEN XiaoMing CUI XiangDong WANG YanShan School ofEarth Sciences and Engineering Nanjing University Nanjing 210093 China Exploration and Development Institute Liaohe Oilfield Panjin 124000 China

The oil-rich Damintun Depression is located in the Liaohe Basin, Northeast China, and was formed during the Paleogene. The major oil-producing strata in the depression are mudstone and shale. To explore the burial diagenetic history of the basin and the formation thresholds of hydrocarbons, the characters of the kaolinite subgroup minerals and mixed-layer illite/smectite in the mudstone and the shale are studied by using X-ray diffraction, electron probe, scanning electron microscope, and Fourier infrared spectrum. The kaolinite subgroup consists of kaolinite and halloysite. The kaolinite is flake-like or vermiform-like. The halloysite is in long tubular shape and its length is related to its iron content. A longer tube has lower iron content. The crystallinity of kaolinite is 0.40 ~20, and its degree of order increases from 0.03 to 1.17 with the burial depth. Kaolinite is in disorder when the buried depth is less than or equal to 2479 m, and it is partially ordered when the buried depth is greater than 2479 m. Kaolinite is supposed to turn into dickite when the depth is greater than 2550 m, but low penetrability and low poros- ity of the shale and mudstone prevent such a change. The mixed-layer illite/smectite changes from disorder to order continually as the buried depth increases. Its disorder （RoI/S）, as defined by illite layer content （I%）, is smaller than 50% at depths less than 2550.25 m. Based on Hoffman ＆ Hower＇s model, the paleo-geothermal gradients of 3.37-3.76℃/100 m （3.57℃/100 m on average） can be derived in the Paleocene Damintun Depression, which is significantly higher than the present geothermal gradient （2.9℃00 m）. The threshold depth of the oil formation in the depression is about 2550 m.

关键词： Damintun Depression Paleogene kaolinite halloysite mixed-layer illite/smectite mixed-layer illite/smectite geother-mometer paleo-geothermal gradient

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Pull-out Behaviour of Axially Loaded Screwed-in Threaded Rods Embedded in CLT Elements: Experimental Study

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Journal of Renewable Materials 2022年第1期10卷 105-117页

作者： Huifeng Yang junfeng ji Haotian Tao Benkai Shi Junbin Hu Bo Wen Nanjing Tech University Nanjing211816China Southeast University Nanjing211189China Sanjiang University Nanjing210012China

Experimental investigation on the pull-out behaviour,including the withdrawal capacity,slip stiffness and inter-facial shear stress,of axially loaded screwed-in threaded rod embedded in cross laminated timber(CLT)was *** with varying embedment length and different number of threaded rods were tested in this *** prevent premature splitting failure of timber,some specimens were reinforced in the direction perpen-dicular to the timber grain with self-tapping *** results showed that the screwed-in threaded rod con-nections exhibited good pull-out behaviour with high withdrawal capacity and slip *** a certain range,the withdrawal capacity increases considerably with the increase of embedment length,while the average interfacial shear stress shows the opposite *** self-tapping screws played an important role on reducing the splitting of the timber and improving the withdrawal capacity and slip stiffness of the screwed-in threaded ***,for the specimens with self-tapping screw reinforcements,the improvement of withdrawal capacity and stiffness when increasing the number of threaded rods are much more obvious than that of the speci-mens without the self-tapping screws,due to the change of failure modes.

关键词： Threaded rods screwed-in pull-out behaviour timber structure experimental study

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Environmental changes during the past 13500 cal. a BP deduced from lacustrine sediment records of Lake Qinghai, China

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Chinese Journal Of Geochemistry 2011年第4期30卷 479-489页

作者： WANG Yong SHEN ji XU Xingna LIU Xingqi SIROCKO Frank ZHANG Enlou ji junfeng State Key Laboratory of Lake Science and Environment Nanjing Institute of Geography and Limnology Nanjing 210008 China Max Planck Institute of Chemistry Mainz 55020 Germany Institute of Geoscience University ofMainz Mainz 55099 Germany School of Geographical Science Southwest University Chongqing 400715 China Department of Earth Sciences Nanjing University Nanjing 210093 China

A 475-cm long sediment core (QH-2005) from Lake Qinghai was used to carry out multi-proxy analysis of δ18O and body length of ostracod valves and redness and grain size of sediments, in order to reconstruct environ-mental changes during the past 13500 cal. a BP. The age model was based on 6 14C dates for bulk orgnic carbon (BOC) and 2 14C dates for lignin. The lignin 14C dates are apparently younger than the corresponding layers' BOC 14C dates, indicating that the reservoir age varied from 728 to 1222 a since the Late Glacial and from 2390 to 2490 a immediately before the pre-bomb era. Hence, the 14C age model for Core QH-2005 was corrected by the changing reservoir age. Ostracod δ18O values were primarily related to dilution and evaporative enrichment of the lake water. The reconstructed salinity based on ostracod body length coincides well with ostracod δ18O values. High redness and mean grain size (MZ) values indicate increased riverine supply to Lake Qinghai associated with increasing monsoon rainfall. Multi-proxy results show that climate during 13500-10900 cal. a BP was relatively cold and dry with fre-quent short-term fluctuations; a warm and wet climate began at about 10900 cal. a BP and culminated around 6500 cal. a BP as a result of monsoon strengthening; the climate became cold and dry afterwards and has remained rela-tively stable since 3400 cal. a BP. Our data also reveal short-term (millennial/centennial timescales) climatic fluctua-tions including: Younger Dryas events, ice-rafting events 8 and 1 (by ～11000 cal. a BP and ～1600 cal. a BP respec-tively), 8200 cal. a BP cold event, Little Ice Age and the Medieval Warm Period.

关键词： CAL 湖泊沉积记录青海湖 BP 环境平均晶粒尺寸气候变化中国

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Seasonal variations in the Sr-Nd isotopic compositions of suspended particulate matter in the lower Changjiang River:Provenance and erosion constraints

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Chinese Science Bulletin 2011年第22期56卷 2371-2378页

作者： MAO ChangPing CHEN Jun YUAN XuYin YANG ZhongFang ji junfeng Institute of Surficial Geochemistry School of Earth Sciences and Engineering Nanjing University Nanjing 210093 China College of Environmental Science and Engineering Hohai University Nanjing 210098 China School of Earth Science and Resources China University ofGeosciences (Beijing) Beijing 100083 China

Suspended particulate matter samples were collected monthly for more than 2 years in Nanjing,China to examine seasonal changes in the Sr-Nd isotopic compositions of the lower Changjiang River(CR).The results indicate that the 87Sr/86Sr ratios of the samples ranges from 0.725352 to 0.738128,and the values ofεNd(0)ranges from-10.55 *** Sr-Nd isotopic compositions show distinct seasonal *** samples had lower 87Sr/86Sr ratios and higherε Nd(0)values during the flood season than the dry *** seasonal variations primarily reflect the controls of provenance rocks and erosion in different *** relative decrease in 87Sr/86Sr ratios and the increase inε Nd(0)values during the flood season may reflect an increasing in the mechanical erosion rate in the upper basin and the contribution of more sediment from the upper *** end member values of 87Sr/86Sr andε Nd(0)of the samples were 0.728254 and?11.26,respectively.

关键词：同位素组成悬浮颗粒物季节变化侵蚀率 Sr Nd 长江季节性变化

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Variation of Zr/Rb ratios on the Loess Plateau of Central China during the last 130000 years and its implications for winter monsoon

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Chinese Science Bulletin 2002年第15期47卷 1298-1302页

作者： LIU Lianwen CHEN Jun CHEN Yang ji junfeng LU Huayu Institute of Surficial Geochemistry State Key Laboratory of Mineral Deposit ResearchDepartment of Earth SciencesNanjing UniversityNanjing 210093China Institute of Earth Environment Chinese Academy of Sciences

To find a new index of winter monsoon without effects of chemical weathering and pedogenesis is an important task in loess research. Chemical analysis of five grain size fractions (i.e. >32μm, 32-20μm, 20-8μm, 8-2μm and <2μm) show that Zr is enriched in coarser grain size, while Rb is concentrated in finer fractions. An excellent correlation occurs between Zr/Rb ratios and mean grain size in loess units (L1LL1 and L1LL2) from Huanxian and Xifeng sections, reflecting that Zr/Rb ratios increase when grain size is coarser. Due to immobility of the two elements during the postdepositional process, Zr/Rb ratios can eliminate the effect of weathering and pedogenesis and serve as an excellent proxy on winter monsoon variation. The Zr/Rb ratio curves of the Huanxian, Xifeng and Luochuan sections during the last 130000 years show that the winter monsoon strength was very weak during MIS 3, which corresponded to the intensity during MIS 5.

关键词： loess index of winter monsoon Zr/Rb ratios grain size.

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