Loess magnetic properties in the Ili Basin and their correlation with the Chinese Loess Plateau

     Over the past two decades, magnetoclimatological studies of loess-paleosol sequences in the Chinese Loess Plateau (CLP) have made outstanding achievements, which greatly promote the understanding of East Asian paleomonsoon evolution, inland aridification of Asia, and past global climate changes. Loess magnetic properties of the CLP have been well studied. In contrast, loess magnetic properties from outside the CLP in China have not been fully understood. We have little knowledge about the magnetic properties of loess in the Ili Basin, an intermontane depression of the Tianshan (or Tien Shan) Mountains. Here, we present the results of rock magnetic measurements of the Ili loess including mass magnetic susceptibility (χ) and anhysteretic remanent magnetization (ARM), high/low temperature dependence of susceptibility (TDS) and hysteresis, as well as X-ray diffraction (XRD) for mineral analysis. Based on the comparison with loess-paleosol sequences in the CLP (hereafter referred to as the Chinese loess), we discuss the possible magnetic susceptibility enhancement mechanism of the Ili loess. The results show that 1) the total magnetic mineral concentration of the Ili loess is far lower than that of the Chinese loess, though they have similar magnetic mineral compositions. The ferrimagnetic minerals in the Ili loess are magnetite and maghemite, and the antiferromagnetic mineral is hematite; XRD analysis also identifies the presence of ilmenite. The ratio of maghemite is lower in the Ili loess than in the Chinese loess, but the ratios of magnetite and hematite are higher in the Ili loess than in the Chinese loess. 2) The granularity of magnetic minerals in the Ili loess, dominated by pseudo-single domain (PSD) and multi-domain (MD) grains, is generally much coarser than that of the Chinese loess. Ultrafine pedogenically-produced magnetic grains have a very limited contribution to the susceptibility enhancement. Rather, PSD and MD particles of magnetite and maghemite are the main contributors to the enhancement of susceptibility in the Ili loess. 3) The susceptibility enhancement mechanism for the Ili loess is complicated and superimposes both a wind velocity/vigor model (Alaskan or Siberian model) and the in situ ultrafine grain pedogenic model; the former might play an important role in the Ili loess. 4) Magnetic susceptibility enhancements of the Ili loess are related not only to the eolian input of the source area, but also to the local climate, landform, and geological background. Therefore, great care should be taken when reconstructing paleoclimate using magnetic susceptibility data from the Ili loess.

泥河湾盆地大长梁剖面岩石磁学和环境磁学研究

The fluvio-lacustrine sequence in the Nihewan Basin is an important archive of late Pliocene-Pleistocene climate and environment changes in temperate northern China, which provides excellent sources of early human settlements in high latitude East Asia. The recent years have witnessed a considerable progress in the paleomagnetic dating of its stratigraphy, which has notably increased our understanding of a series of important issues such as the early human occupation in the Old World, the infilling history of the Nihewan Basin, and the chronological sequence of the Nihewan faunas. Up to now, the long-term paleoenvironmental changes directly retrieved from this basin, which might influence the evolution and expansion of early humans in the Nihewan Basin, are still poorly constrained, although several paleoclimatic records have been retrieved from this area. In this study, a combined mineral-magnetic and geochemical investigation was carried out on the fluvio-lacustrine sequence from the Dachangliang section at the eastern margin of the basin in order to reveal its rock magnetic and environmental magnetic characteristics and its implications for early human evolution in East Asia. The major findings and conclusions are listed as the following: First, there is an increased cooling coupled with an intensified aridification recorded in the fluvio-lacustrine sequence of the Dachangliang section. The cooling is related to an up-section decrease in propensity to chemical weathering as inferred from an increase in low-field susceptibility after cycling to 700 °C. Close to 700 °C, reacting chlorite is providing the iron source for newly formed very fine-grained ferrimagnetic minerals which enhances the susceptibility signal. The reactivity of chlorite after annealing at temperatures above 600 °C is documented with X-ray diffraction. Second, degrees of chemical weathering in the Nihewan Basin are further estimated by clay mineralogy (i.e. chlorite and illite contents and chlorite/illite ratio) and a series of major element proxies (i.e. Na2O/Al2O3 versus K2O/Al2O3 diagram, Al2O3-(CaO + Na2O)-K2O ternary diagram (A-CN-K), chemical index of alteration (CIA), (CaO + Na2O + MgO)/TiO2, (CaO + Na2O + MgO + K2O)/(TiO2 + Al2O3), CaO/Al2O3 and CaO/TiO2). The up-section decrease in propensity to chemical weathering suggested by the aforementioned rock mangetic measurement is further confirmed by these geochemical analyses. Combining the chemical weathering records from the Nihewan Basin, Chinese Loess Plateau, South China Sea and eastern China, we find that the consecutive decreasing trend in chemical weathering intensity during the late Cenozoic is ubiquitous across China. This pattern may result from a long-term decreasing East Asian summer monsoon and increasing East Asian winter monsoon, and thus a consecutive increasing of aridification and cooling in Asia during the Quaternary. Furthermore, the chemical weathering intensity increased from South China to North China during the Quaternary, in line with the decreasing East Asian summer monsoon and increasing East Asian winter monsoon and thus the gradually intensified aridification and cooling from South China to North China. Third, a combined mineral-magnetic and geochemical investigation provides evidences that the large-amplitude alterations of concentration of magnetic minerals mainly result from preservation/dissolution cycles of detrital magnetic minerals in alternately oxic and anoxic depositional environments. The preservation/dissolution model implies that the high-magnetic and low-magnetic cycles of this sedimentary sequence represent glacial and interglacial climate cycles, respectively. This contribute significnatly to our understanding of the link between climate and magnetic properties. Finally, the paleoclimatic implications of these rock magnetic and geochemical characteristics significantly increase our understanding of the general setting of early humans in high northern latitude in East Asia. We propose that the cold and dry climate may have contributed significantly to the expansion and adaptation of early humans, rather than bringing hardship, as is often thought. The relationship between magnetic properties and climate possibly provides valuable information on the climatic context of the Paleolithic sites in the basin, especially whether the occupation occurred during an interglacial or glacial period.

Source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern North Atlantic

Magnetic properties of eight particle size ranges from nine locations in Iceland and 26 locations in southern Greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment. These terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand. Fine pseudo-single domain (PSD) size magnetic grains dominate the magnetic assemblage of all Icelandic fractions. In contrast, Greenlandic samples possess greater variation in magnetic grain size; only fine silt and clay are as magnetically fine as the Icelandic PSD grains, while Greenlandic silts and sands are dominated by coarser PSD and multi-domain grains. These observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration-dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between Icelandic and Greenlandic sources. Using these results to examine magnetic grain size records from marine sediment cores collected across the northern North Atlantic suggests that source, not just transport-controlled physical grain-size, has a significant impact on determining the magnetic grain size at a particular location. Homogeneity of magnetic grain size in Icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding Iceland and their ability to buffer large environmental changes. © 2013 Elsevier B.V.

Sediment magnetic properties of glacial till deposited since the Little Ice Age maximum for selected glaciers at Svartisen and Okstindan, northern Norway

Samples of glacial till deposited since the Little Ice Age (LIA) maximum by two glaciers, North Bogbre at Svartisen and Corneliussen-breen at Okstindan, northern Norway, were obtained from transects running from the current glacier snout to the LIA (c. AD 1750) limit. The samples were analysed to determine their sediment magnetic properties, which display considerable variability. Significant trends in some magnetic parameters are evident with distance from the glacier margin and hence length of subaerial exposure. Magnetic susceptibility (X) decreases away from the contemporary snout, perhaps due to the weathering of ferrimagnetic minerals into antiferromagnetic forms, although this trend is generally not statistically significant. Trends in the ratios of soft IRM/hard IRM which are statistically significant support this hypothesis, suggesting that antiferromagnetic minerals are increasing relative to ferrimagnetic minerals towards the LIA maximum. Backfield ratios (IRM -100 mT/SIRM) also display a significant and strong trend towards magnetically harder behaviour with proximity to the LIA maximum. Thus, by employing a chronosequence approach, it may be possible to use sediment magnetics data as a tool for reconstructing glacier retreat in areas where more traditional techniques, such as lichenometry, are not applicable.

Correlation of properties of Brazilian Haplustalfs with magnetic susceptibility measurements

Magnetic susceptibility (chi, mass specific) is useful for easy indirect estimation of other soil properties at a low cost. The aim of this study was to assess the use of chi as measured with an analytical balance for predicting properties with a substantial influence on the management of Typic Haplustalfs in southern Brazil. To achieve this 48 topsoil samples were taken at the intersection points in a rectangular grid of 20 m x 20 m cells, with 38 of these used for calibration and 10 for validation in regression analyses. The obtained chi values were slightly higher than, and highly correlated (r = 0.970; P < 0.001) with those measured with a susceptibility meter. Highly significant (P < 0.001) correlations were also found between chi and other soil properties relevant to soil classification and management such as clay content (r = 0.68), cation exchange capacity (r = 0.62), P sorption capacity (r = 0.76) and haematite content (r = 0.82). Results from a principal component analysis of eight properties important for soil classification explained 11% of the variance in the data set. The good predictive ability of chi was consistent with current knowledge on the formation pathways for pedogenic ferrimagnets. In summary, chi, which can be readily measured with an analytical balance, has the potential for quantifying soil attributes and may therefore be used in pedotransfer functions.

Magnetic and mineralogical analyses of Ganzi and Luochuan sections

We present a first combined environmental magnetic and geochemical investigation of a loess-paleosol sequence (<55 ka) from the Chuanxi Plateau on the eastern margin of the Tibetan Plateau. Detailed comparison between the Ganzi section and the Luochuan section from the Chinese Loess Plateau (CLP) allows quantification of the effects of provenance and climate on pedogenic magnetic enhancement in Chinese loess. Rare earth element patterns and clay mineral compositions indicate that the Ganzi loess originates from the interior of the Tibetan Plateau. The different Ganzi and CLP loess provenances add complexity to interpretation of magnetic parameters in terms of the concentration and grain size of eolian magnetic minerals. Enhanced paleosol magnetism via pedogenic formation of ferrimagnetic nanoparticles is observed in both sections, but weaker ferrimagnetic contributions, finer superparamagnetic (SP) particles and stronger chemical weathering are found in the Ganzi loess, which indicates the action of multiple pedogenic processes that are dominated by the combined effects of mean annual precipitation (MAP), potential evapotranspiration (PET), organic matter and aluminium content. Under relatively high MAP and low PET conditions, high soil moisture favours transformation of ferrimagnetic minerals to hematite, which results in a relatively higher concentration of hematite but weaker ferrimagnetism of Ganzi loess. Initial growth of superparamagnetic (SP) particles is also documented in the incipient loess at Ganzi, which directly reflects the dynamic formation of nano-sized pedogenic ferrimagnets. A humid pedogenic environment with more organic matter and higher Al content also helps to form finer SP particles. We therefore propose that soil water balance, rather than solely rainfall, dominates the type, concentration and grain size of secondary ferrimagnetic minerals produced by pedogenesis.

(Table 1) Rock magnetic parameters of core samples obtained from Morne Rouge, Ile de Possession

The magnetic high field susceptibility chi(hifi) indicates the presence of mafic paramagnetic minerals in the scoriae and points to an absence of clay minerals, and in turn of pedogenic processes, in the peat samples. Due to their volcanic origin, scoriae contain much more ferrimagnetic minerals than peat with is indicated by their enhanced saturation remanence Mrs.

Mineral-magnetic record of Late Quaternary climatic changes in a high Alpine lake

The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations. According to pollen data, the sediments extend from the present to the Younger Dryas, i.e., they cover more than 10,000 years of environmental change in the Alps. The major change in magnetic properties corresponds to the climatic warming of the early Holocene. High-coercivity magnetic minerals that characterize the Late Glacial period almost disappeared during the Holocene and the concentration of ferrimagnetic minerals increased sharply. The contribution of superparamagnetic grains also decreased in the Holocene sediments. Similar variations in {SP} content and coercivity, of smaller magnitude, are found in the Holocene and are interpreted to represent minor climatic variations. Comparison with the historical record of the last 1000 years confirms this interpretation. The magnetic mineralogy, the superparamagnetic contents, and the {IRM} intensity in the coarse-grained, Late Glacial sediments are similar to those measured in the catchment bedrock. This indicates a detrital origin. The different properties and the higher concentration of magnetic minerals in the Holocene sediments are due to authigenic phases. Magnetic properties provide a high resolution record of climatic change. They are sensitive even to small variations that are not recorded in the pollen or {LOI} data. Magnetic parameters show fine-scale variation and constitute a valuable supplement to conventional climatic indicators.

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before  ∼  320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

Raman spectroscopy of the molybdate minerals chillagite (tungsteinian wulfenite-I4), stolzite, scheelite, wolframite and wulfenite

Raman spectra of chillagite, wulfenite, stolzite, scheelite and wolframite were obtained at 298 and 77 K using a Raman microprobe in combination with a thermal stage. Chillagite is a solid solution of wulfenite and stolzite. The spectra of these molybdate minerals are orientation dependent. The band at 695 cm-1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The bands at 790 and 881 cm-1 are associated with the antisymmetric and symmetric Ag modes of terminal WO2 whereas the origin of the 806 cm-1 band remains unclear. The 4(Eg) band was absent for scheelite. The bands at 353 and 401 cm-1 are assigned as either deformation modes or as r(Bg) and (Ag) modes of terminal WO2. The band at 462 cm-1 has an equivalent band in the infrared at 455 cm-1 assigned as as(Au) of the (W2O4)n chain. The band at 508 cm-1 is assigned as sym(Bg) of the (W2O4)n chain.

An infrared spectroscopic study of the some Autunite minerals

A series of selected autunites with phosphate as the anion have been studied using infrared spectroscopy. Each autunite mineral has its own characteristic spectrum. The spectra for different autunites with the same composition are different. It is proposed that this difference is due to the structure of water and hydrated cations in the interlayer region between the uranyl phosphate sheets. This structure is different for different autunites. The position of the water hydroxyl stretching bands is related to the strength of the hydrogen bonds as determined by hydrogen bond distance. The highly ordered structure of water is also observed in the water HOH bending modes where a high wavenumber bands are observed. The phosphate and uranyl stretching vibrations overlap and are obtained by curve resolution.

Raman microscopy of the molybdate minerals koechlinite, iriginite and lindgrenite

A series of molybdate bearing minerals including wulfenite, powellite, lindgrenite and iriginite have been analysed by Raman microscopy. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the paragenetic relationships between the minerals. The molybdenum bearing minerals lindgrenite, iriginite and koechlinite were studied by scanning electron microscopy and compositionally analysed by EDX methods using an electron probe before Raman spectroscopic analyses. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra.

Raman spectroscopy of the copper chloride minerals nantokite, eriochalcite and claringbullite - implications for copper corrosion

The application of Raman spectroscopy to the study of the copper chloride minerals nantokite, eriochalcite and claringbullite has enabled the vibrational modes for the CuCl, CuOH and CuOH2 to be determined. Nantokite is characterised by bands at 205 and 155 cm-1 attributed to the transverse and longitudinal optic vibrations. Nantokite also has an intense band at 463 cm-1, eriochalcite at 405 and 390 cm-1 and claringbullite at 511 cm-1. These bands are attributed to CuO stretching modes. Water librational bands at around 672 cm-1 for eriochalcite have been identified and hydroxyl deformation modes of claringbullite at 970, 906 and 815 cm-1 are observed. Spectra of the three minerals are so characteristically different that the minerals are readily identified by Raman spectroscopy. The minerals are often determined in copper corrosion products by X-ray diffraction. Raman spectroscopy offers a rapid, in-situ technique for the identification of these corrosion products.

Raman spectroscopic study of the magnesium carbonate minerals– artinite and dypingite

Magnesium minerals are important in the understanding of the concept of geosequestration. The two hydrated hydroxy magnesium carbonate minerals artinite and dypingite have been studied by Raman spectroscopy. Intense bands are observed at 1092 cm-1 for artinite and at 1120 cm-1 for dypingite attributed CO32- ν1 symmetric stretching mode. The CO32- ν3 antisymmetric stretching vibrations are extremely weak and are observed at1412 and 1465 cm-1 for artinite and at 1366, 1447 and 1524 cm-1 for dypingite. Very weak Raman bands at 790 cm-1 for artinite and 800 cm-1 for dypingite are assigned to the CO32- ν2 out-of-plane bend. The Raman band at 700 cm-1 of artinite and at 725 and 760 cm-1 of dypingite are ascribed to CO32- ν2 in-plane bending mode. The Raman spectrum of artinite in the OH stretching region is characterised by two sets of bands: (a) an intense band at 3593 cm-1 assigned to the MgOH stretching vibrations and (b) the broad profile of overlapping bands at 3030 and 3229 cm-1 attributed to water stretching vibrations. X-ray diffraction studies show the minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality and explains why the Raman spectra of these minerals have not been previously or sufficiently described.