scholarly journals Holocene Environmental Changes Inferred From an Aeolian-Palaeosol-Lacustrine Profile in the Mu Us Desert, Northern China

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaokang Liu ◽  
Ruijie Lu ◽  
Zhiyong Ding ◽  
Zhiqiang Lyu ◽  
Yijing Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Susceptibility ◽  
Environmental Changes ◽  
Chemical Elements ◽  
Lacustrine Sediments ◽  
Northern China ◽  
Depositional Environments ◽  
Forest Steppe ◽  
Mu Us Desert ◽  
Average Grain Size

An excavated profile of aeolian-palaeosol-lacustrine sediments (the Wapianliang profile), located at the southeastern part of the Mu Us Desert, Northern China, was studied to reconstruct regional Holocene environmental changes. A chronology was established based on three AMS 14C and two OSL dates, and variations in the lithology and grain size, magnetic susceptibility, soil micromorphology, and chemical elements were used to explore the regional depositional environments during the Holocene. The results showed that since around 14 ka BP, this region had experienced seven alternations of wetting and drying. A shallow lake, which was identified by celadon lacustrine sediments with sporadic freshwater gastropod fossils, occurred in this area from around 13.0 ka BP to 9.9 ka BP. There existed two obvious intervals of soil formation, inferred from the environmental proxies of the palaeosol/sandy palaeosol layers, with relatively fine average grain-size, high magnetic susceptibility value, remarkable pedogenesis features, and strong chemical weathering, in particular, a well-developed palaeosol layer dating from the middle Holocene (8.6 ka BP to 4.2 ka BP). A weakly-developed palaeosol layer (from around 1.2 ka BP) at the upper part of the profile is possibly an indication of the Medieval Warm Period. This implies a forest steppe environment at both of these sedimentary stages. After 0.9 ka BP, a desert environment returned, analogous to before around 13.0 ± 1.4 ka BP, between 9.9 ± 1.1 ka BP to 8.6 ka BP, and between 4.2 ka BP to 1.6 ka BP, indicating the aggravation of aeolian activity and the expansion of mobile sand dunes. The variations in sedimentary environments were mainly triggered by changes in the East Asian Summer Monsoon (EASM).

scholarly journals Changing depositional environments in the Colombian Fúquene Basin at submillennial time-scales during 284-27 ka from unmixed grain-size distributions and aquatic pollen

2012 ◽  
Vol 91 (1-2) ◽  
pp. 199-214 ◽  
Author(s):  
M. Vriend ◽  
M.H.M. Groot ◽  
H. Hooghiemstra ◽  
R.G. Bogotá-Angel ◽  
J.C. Berrio
Keyword(s):  
Grain Size ◽  
Lacustrine Sediments ◽  
Depositional Environments ◽  
Organic Carbon Content ◽  
Size Distributions ◽  
Glacial Cycles ◽  
Available Energy ◽  
Grain Size Distributions ◽  
Drilling Site ◽  
Mis 5E

AbstractIn a ~60 m long record reflecting the period from 284 ka to 27 ka we analysed grain size distributions (GSD), organic carbon content, and aquatic pollen assemblages at 1-cm increments. The 4768-points time series show with ~60 yr resolution the dynamic history of Lake Fúquene (2540 m alt., 4° N lat.) of the northern Andes during two full interglacial-glacial cycles. GSD show proportions of clay, fine silt, coarse silt, and sand evidencing the location of the sediment source (proximal vs distal) in relation to the drilling site, and available energy to transport sediments in the catchment area. Loss-on-ignition (LOI) values reflect estimates of the abundance of organic matter (OM) in the sediments. Aquatic pollen were grouped into assemblages characteristic of deep water, shallow water, swamp, and wet lake shore environments, reflecting a hydrological gradient sensitive for lake level changes.The End-Member Modelling Algorithm (EMMA) showed that 4 end-members (EMs) explain an optimal proportion (70%) of the observed variation. EMMA is able to unmix GSD of lacustrine sediments in a genetically meaningful way allowing EMs to be interpreted in past depositional and environmental settings. Most unexplained variability is located in the fraction of coarse sediment. OM content was estimated on the basis of LOI data and formed a fifth EM that mainly indicates presence of peat. Changes concur with submillennial-scale variability established in other proxies from this record (Groot et al., 2011). Periods with distinct sediment compositions are 284-243 ka (mainly MIS 8), 243-201 ka (mainly MIS 7), 201-179 ka (mainly MIS 7/6 transition), 179-133 ka (mainly MIS 6), 133-111 ka, (mainly MIS 5e) 111-87 ka (mainly MIS 5d-5b), 87-79 ka (mainly MIS 5a), 79-62 ka (mainly MIS 4), and 62-27 ka (MIS 3) showing sedimentological regimes are climate driven.

Grain size and geochemical study of the surface deposits of the sand dunes in the Mu Us desert, northern China

2016 ◽  
Vol 52 (6) ◽  
pp. 1009-1019 ◽  
Author(s):  
Bing Liu ◽  
Heling Jin ◽  
Liangying Sun ◽  
Zhong Sun ◽  
Caixia Zhang
Keyword(s):  
Grain Size ◽  
Sand Dunes ◽  
Northern China ◽  
Mu Us Desert ◽  
Geochemical Study

scholarly journals Geochemical differentiation of atmospheric aerosols in natural zones of European Russia

2021 ◽  
Vol 906 (1) ◽  
pp. 012048
Author(s):  
Tatiana Kuderina ◽  
Otto Chkhetiani ◽  
Arseni Kudikov ◽  
Maria Artamonova
Keyword(s):  
Atmospheric Aerosols ◽  
Environmental Changes ◽  
Chemical Elements ◽  
Agricultural Landscapes ◽  
European Russia ◽  
Russian Plain ◽  
Forest Steppe ◽  
Anthropogenic Landscapes ◽  
Forest Zone ◽  
Natural Zones

Abstract Climate and environmental changes on Earth have become modern challenges to humanity. The main factor affecting the landscapes of Russia is an increase in air temperature and a decrease in precipitation. Because of these processes, the amount of aerosols in the near-ground atmosphere of the landscapes of the ETR (European territory of Russia) increases. The aim of the study is to determine the atmogeophysical and atmogeochemical indicators that reveal the interaction of the atmosphere and the diversity of natural landscapes in European Russia. Landscape-geochemical research methods make it possible to study geosystems with the participation of all landscape components and actual migration processes, especially the atmospheric migration of chemical elements. To determine the modern atmogeochemical existence, field comprehensive studies of the potential emission of matter in all natural zones of the ETR were carried out submeridionally - in the landscapes of the steppe, forest-steppe, forest and tundra zones of the ETR. The research results show that in the submeridional profile, the mass concentration of aerosols decreases regularly from south to north, the minimum concentrations of atmospheric aerosols are observed in the forest zone, in the tundra there was a slight increase due to anthropogenic landscapes and the influence of the sea. Analysis of the chemical composition of aerosols revealed that, among the elements of global importance, aluminosilicates naturally increase to the south of the ETR as elements of clay minerals that are widespread in the Russian Plain. The maximum phosphorus content occurs in the residential area with agricultural landscapes. Sulfur concentrations are confined to the semiarid zone of the ETR, then decrease in the forest zone and increase again in the technogenic regions and the tundra belt of the Kola Peninsula, surrounded by the sea. The concentrations of chemical elements of regional and local distribution in atmospheric aerosols are more differentiated on the ETR and depend on the natural and technogenic features of each region. Thus, heavy metals are more common in the Plain territories of the forest-steppe and forest zones of the ETR and are confined to the bedrock and technogenic sources. High concentrations of calcium and strontium are associated with areas of weathering of carbonate rocks. In general, increased concentrations of atmospheric aerosols with an increased content of anthropogenic elements are observed during the western and southern transport of air masses. At the same time, the amount of rainstorm precipitation increases when these aerosols act as condensation nuclei. To assess the current state of the atmosphere at the ETR, it is necessary to continue field measurements and organize European annual and seasonal geochemical monitoring at stationary observation points.

scholarly journals Climate Change and Vegetation Evolution during the Transition from Marine Isotope Stage 5 to 4 Based on Two Typical Profiles at the Southern Chinese Loess Plateau

2020 ◽  
Vol 12 (4) ◽  
pp. 1372
Author(s):  
Tieniu Wu ◽  
Huaqing Wu ◽  
Henry Lin ◽  
Tiantian Yang ◽  
Xiaoyang Wu ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Susceptibility ◽  
Loess Plateau ◽  
Transitional Period ◽  
Marine Isotope Stage ◽  
Chinese Loess Plateau ◽  
Forest Steppe ◽  
Chinese Loess ◽  
Southern Chinese ◽  
Mis 5

The geological transitional period from the Marine Isotope Stage (MIS) 5 to 4 during the Quaternary period is a multidimensional change involving monsoon and precipitation variation, vegetation dynamics, and environmental evolution. The first loess layer (L1) and the first paleosol layer (S1) in the Chines Loess Plateau provide excellent high-resolution terrestrial sediment record for this transition. In this work, grain size (GS), CaCO3 content, magnetic susceptibility (MS), and pollen composition were measured at intervals of 2-cm in two representative L1/S1 profiles in the southern Chinese Loess Plateau to reconstruct records of climatic and vegetative changes during this transition. Our results showed that, in general, the paleo-vegetation type was forest-steppe, with Pinus being the commonest tree, and Chenopodiaceae and Artemisia being common herbs in the study area. The topography had a significant impact on the distribution of paleo-vegetation. The increase of coarse particles, the decrease of magnetic susceptibility, and the rising percentage of Gramineae, Artemisia and Chenopodiaceae pollen, all indicated that the paleoclimate became cooler and drier over the transitional period. Besides, we identified a cool event at about 76.8 ka B.P. as revealed by grain-size curves, and in response to this event, the vegetation changed significantly but lagged several hundred years behind the grain size record. This study confirmed the cooling and drying tendency during the MIS 5 to 4 transition phase in the southern margin of the Chinese Loess Plateau. These findings shed light on the climatic change on vegetation evolution during the MIS 5 to 4 transition period.

scholarly journals A model for the domestication of Panicum miliaceum (common, proso or broomcorn millet) in China

2020 ◽  
Author(s):  
Chris J. Stevens ◽  
Gideon Shelach-Lavi ◽  
Hai Zhang ◽  
Mingyu Teng ◽  
Dorian Q. Fuller
Keyword(s):  
Grain Size ◽  
Northern China ◽  
Archaeological Sites ◽  
Small Scale ◽  
Initial Increase ◽  
Panicum Miliaceum ◽  
Continuous Increase ◽  
Broomcorn Millet ◽  
Average Grain Size ◽  
Domestication Selection

Abstract This paper outlines a model for the domestication of Panicum miliaceum (broomcorn millet) in Northern China. Data from 43 archaeological sites indicate a continuous increase in average grain size between 6000 and 3300 bc. After this date there is a divergence, with grain size continuing to increase in some populations, while others show no further size increase. The initial increase in grain size is attributed to selection during domestication, while later divergence after 3300 bc is interpreted as resulting from post-domestication selection. Measurements of grains from two archaeological populations of P. ruderale, showed grains were longer in length by 3300 bc than the earliest grains of P. miliaceum. This suggests this sub-species includes many feral, weedy and/or introgressed forms of P. miliaceum and therefore is probably not entirely representative of the true wild ancestor. It is argued that changes from shattering to non-shattering are contemporary with increasing grain size and the commencement of cultivation. The window of P. miliaceum domestication is therefore likely to lie between 7000 and 3300 bc. However, it is probable that a lengthy period of millet harvesting and small-scale management preceded its domestication.

scholarly journals The Elements and Color of Lacustrine Record Revealed Lake Environmental Changes in Semiarid Northern China: A Case Study From Chagan Nur Lake of Southern Mongolian Plateau

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhong Wang ◽  
Guoqiang Li ◽  
Xiaoyan Wang ◽  
Siyi Gou ◽  
Yanqing Deng ◽  
...  
Keyword(s):  
Lake Level ◽  
Environmental Changes ◽  
Lacustrine Sediments ◽  
Northern China ◽  
Vegetation Coverage ◽  
Surface Erosion ◽  
Pollen Record ◽  
Mongolian Plateau ◽  
The Holocene ◽  
Precipitation Changes

The lakes at the southern Mongolian Plateau are sensitive to the variation of EASM changes during the Holocene, and hence the lacustrine records of these lakes provide prospects for understanding how lake environmental changes respond to EASM variation at different timescales. The interpretation of proxy indexes of lacustrine sediments is complex due to the various climatic or/and environmental factors influencing the processes during deposition and after deposition. In this study, the elements and colors of an 11.7-m lacustrine record from Chagan Nur at the southern Mongolian Plateau of northern China were analyzed to constrain the lake environmental changes during the Holocene. The results show that stable elements of Al, Si, K, Ti, Fe, and Rb are more related to surface erosion or/and vegetation coverage, and the variation of Sr is related to the lake-level change in Chagan Nur. The element and color of the lacustrine records show that a small and shallow lake environment occurred at Chagan Nur during 11.7–10.5 ka, the lake level had increased during 10.5–7 ka, and then the lake shrank with strength surface erosion during 7–6.2 ka and from 2 ka to the present. The lake level and surface erosion changes of Chagan Nur have shown a direct response to EASM precipitation changes as reconstructed from the pollen record from the Chagan Nur Lake and other records from northern China.

Study on the Grain Size Characteristics and Magnetic Susceptibility of Aeolian Sediments at Zhuli in Shandong Province: Implications for Paleoclimatic Change

2014 ◽  
Vol 955-959 ◽  
pp. 1355-1359
Author(s):  
Zhi Chao Ni ◽  
Shu Jian Xu ◽  
Xin Chao Ding ◽  
Qiang Li ◽  
Xin Hua Fu
Keyword(s):  
Grain Size ◽  
Magnetic Susceptibility ◽  
High Frequency ◽  
Environmental Changes ◽  
Low Frequency ◽  
Size Class ◽  
Optically Stimulated Luminescence ◽  
Sedimentation Rates ◽  
Chinese Loess ◽  
Aeolian Sediments

Chinese loess-paleosol sequence has archived the most detailed terrestrial records of past climatic and environmental changes. In this study, we concentrate on Zhuli loess section in northern Shandong, by sedimentary and magnetic and optically stimulated luminescence (OSL) methods. Based on the OSL ages, the basal age of the Zhuli section is 60ka extrapolated by sedimentation rates. Grain-size curves indicate that environment-sensitive size fractions of Zhuli section are 39.81-44.67μm and 79.43-89.12μm respectively, by analyzing grain-size class vs. standard deviation values method. The low-frequency magnetic susceptibility has a good correlation with the high-frequency magnetic susceptibility, and the grain size has a good correlation with the magnetic susceptibility.

Surface Modification and its Influence on the Microstructure and Creep Resistance of Nickel Based Superalloy René 77 / Modyfikacja Powierzchniowa Oraz Jej Wpływ Na Mikrostrukture I Wytrzymałosc Na Pełzanie Odlewów Z Nadstopu Niklu Ren´E 77

2013 ◽  
Vol 58 (1) ◽  
pp. 95-98 ◽  
Author(s):  
M. Zielinska ◽  
J. Sieniawski
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Surface Modification ◽  
Turbine Blades ◽  
Processing Parameters ◽  
Grain Structure ◽  
Creep Tests ◽  
Cobalt Aluminate ◽  
Nickel Based Superalloy ◽  
Average Grain Size

Superalloy René 77 is very wide used for turbine blades, turbine disks of aircraft engines which work up to 1050°C. These elements are generally produced by the investment casting method. Turbine blades produced by conventional precision casting methods have coarse and inhomogeneous grain structure. Such a material often does not fulfil basic requirements, which concern mechanical properties for the stuff used in aeronautical engineering. The incorporation of controlled grain size improved mechanical properties. This control of grain size in the casting operation was accomplished by the control of processing parameters such as casting temperature, mould preheating temperature, and the use of grain nucleates in the face of the mould. For nickel and cobalt based superalloys, it was found that cobalt aluminate (CoAl2O4) has the best nucleating effect. The objective of this work was to determine the influence of the inoculant’s content (cobalt aluminate) in the surface layer of the ceramic mould on the microstructure and mechanical properties at high temperature of nickel based superalloy René 77. For this purpose, the ceramic moulds were made with different concentration of cobalt aluminate in the primary slurry was from 0 to 10% mass. in zirconium flour. Stepped and cylindrical samples were casted for microstructure and mechanical examinations. The average grain size of the matrix ( phase), was determined on the stepped samples. The influence of surface modification on the grain size of up to section thickness was considered. The microstructure investigations with the use of light microscopy and scanning electron microscopy (SEM) enable to examine the influence of the surface modification on the morphology of ’ phase and carbides precipitations. Verification of the influence of CoAl2O4 on the mechanical properties of castings were investigated on the basis of results obtained form creep tests.

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