Hematite and goethite, estimated from diffuse reflectance spectra, and magnetic susceptibility (MS) have been determined from both the Luochuan and Lingtai loess sections of the Loess Plateau of central China. Changing concentrations of these iron oxides and MS were used to determine paleoclimatic change. Based on a model that relates pedogenic production of hematite and magnetite to precipitation, we propose two precipitation phases on the Loess Plateau during the last 652.6 Ma. From the Wucheng-Red Clay boundary up to paleosol S5 (MIS 13), precipitation on the Loess Plateau was moderate, probably not frequently exceeding 450 mm/yr, and highly seasonal. From S5 to the present, precipitation during interglacial times has gradually increased to the present levels of 600–650 mm/yr for the localities examined. Throughout the Pleistocene, spanning both glacial and interglacial conditions, hematite to goethite ratios display a consistent decrease. This decrease suggests that precipitation on the Loess Plateau has been getting less seasonal and/or has been occurring during times when temperature was lower. In addition to these long-term changes, it also appears that iron oxide records from the Loess Plateau exhibit 400–500-ka cycles from the Wucheng-Red Clay boundary to S5. These 400–500-ka cycles may be analogous to similar length cycles recorded in δ 13C marine records in the South China Sea and may be linked through weathering and silica production as a result of the Asian monsoon.

Changing color is one of the most striking features of loess–paleosol sequences in central China: the loess is light yellow and the interstratified paleosols are reddish-brown. Until a few years ago, conventional color description of loess sediments was made using a qualitative visual method, the Munsell system. To better understand the character of the color changes and to quantify results, whiteness and magnetic susceptibility were compared from four loess–paleosol sequences. Results show that the two parameters are highly correlated in the four sequences studied. Grain-size analysis and chemical extraction experiments indicate that the concentration and species of fine-grained iron oxides are major factors determining color changes in loess and paleosols. Whiteness and latitude values from the last glacial–interglacial sequence exhibit a linear relationship suggesting that whiteness will be a useful tool for reconstructing past atmospheric circulation, especially the East Asian summer monsoon. Whiteness and magnetic susceptibility in the Luochuan profile over the past 0.9 Myr display a strong correlation indicating that whiteness can be also used to reveal a long climatic history from Chinese loess–paleosol sequences.

Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical properties which are similar except for the thermal instability of the former. Utilising this exception, a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the Luochuan section of the central Chinese Loess Plateau. This investigation has shown that although maghaemite (thermally unstable component) occurs in greater amounts in palaeosols ( M=0.0187 Am kg ±1.1%) than in loess units ( M=0.0156 Am kg ±1.1%), in relative terms its contribution to the ferrimagnetic component of magnetisation is higher in the loess units (Δ M(%)=32.2±2.0) than the soils (Δ M(%)=23.5±3.7). Such an observation suggests that much of the maghaemite component originates in the aeolian source area, with some addition of pedogenic maghaemite occurring in the palaeosols.

QUATERNARY sequences of interbedded aeolian silts (loess) and buried soils (palaeosols) potentially provide one of the best terrestrial records of past climates. Magnetic susceptibility variations in loess and palaeosol sequences from China are strongly correlated with climate-induced fluctuations of oxygen isotope ratios in deep-sea sediments. As an explanation of this correlation, it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non-magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources. It has also been suggested that such a model, involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles, provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations. Here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size. Our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units. This suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non-magnetic loess is inadequate. Our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols.

对最近１３０ｋａ来，洛川黄土－古土壤剖面中绿泥石和云母的分布特征及其与磁化率的关系进行了研究。发现在黄土和古土壤中，云母／绿泥石比值随粒级的减小而增大；在大于８μｍ粒级部分，黄土和古土壤样品的地云母／绿泥石比值相近，而在小于８μｍ的各粒级中，古土壤样品的云母／绿泥石比值较同粒级黄土样品为高，并且这种差别随粒级的减小而加大；洛川黄土剖面中云母／绿泥石比值曲线与磁化率分布曲线十分相似，两者之间存在密切

Abstract Application of reflectance spectra to geologic samples requires a set of standards for materials in concentrations and matrixes similar to those which occur naturally on the earth's surface. Reports the VIS spectra reflectance response to hematite and goethite in geologically meaningful matrixes and compares spectral results to an established analytical technique, XRD. -from Authors

We measured the visible to near-infrared (IR) spectra of 176 synthetic and natural samples of Fe oxides, oxyhydroxides and an oxyhydroxysulfate (here collectively called Fe oxides), and of 56 soil samples ranging widely in goethite/hematite and goethite/lepidocrocite ratios. The positions of the second-derivative minima, corresponding to crystal-field bands, varied substantially within each group of the Fe oxide minerals. Because of overlapping band positions, goethite, maghemite and schwertmannite could not be discriminated. Using the positions of the

The loess record in China constitutes one of the most important archives of past environmental change and specifically, the East Asian monsoon system. Changes in summer monsoon driven pedogenesis are commonly inferred from magnetic susceptibility of loess. However, there is still controversy as to the signal origin and the uncertain effects of sediment accumulation rates. This is linked to a wider problem that is emerging from recent work; that of the relative importance on proxy records such as magnetic susceptibility of both regional climate patterns (i.e. the monsoon) and local site-specific influences, particularly modulated through site-specific sedimentation rate. At present this is poorly constrained and significantly increases the degree of uncertainty over the wider-scale applicability of climate reconstructions from individual sites. To resolve this issue for sub-orbital timescales, a rapidly deployable technique is needed that can be used to test multiple sites and differentiate between local and regional signals. This research develops the first use of full spectrum reflectance spectroscopy in studying loess in the field at one site on the south of the Loess Plateau, and utilises statistical analyses to compare such data with magnetic susceptibility records. Establishment of loess reflectance as a proxy for climate variability will potentially allow extension of the technique from point measurements to an imaging system and so enable the compilation of large data sets in order to investigate lateral facies variations in loess profiles. This may allow the extraction of a broad scale climate record. Field spectra were obtained from 350 to 1100 nm, with red edge reflectance spectra indicating the presence of iron-oxides, previously demonstrated to be indicators of pedogenesis through laboratory measurements. An off the shelf camera was also tested with visible wavelength spectra being useful for rapid but general profile characterisation. In order to mitigate the effects of bidirectional reflectance distribution function (a potential problem in field measurements), further laboratory measurement was made of powdered samples (400 2400 nm). Absorption features indicative of montmorillonite and illite/muscovite were noted and stepwise regression modelling utilising absolute reflectance, first derivative spectra and continuum removed spectra indicated strong predictive relationships with magnetic susceptibility, particularly against the presence of montmorillonite. The abundance of such clay minerals could be used to infer weathering rates and hence be used as a proxy for pedogensis. Reconstructions for the studied site are presented and demonstrate the potential power of loess reflectance environmental reconstruction.

Mn(OH)2 kommt als Mineral Pyrochroit vor. Unter Ausschlu08 von Sauerstoff kann es durch F01llung von Mangan(II)-Salzl02sungen mit Alkali erhalten werden. Mn(OH)2 besitzt eine Schichtstruktur vom CdJ2(I)-Typ1) und ist isostrukturell mit Ca(OH)2. Vermutlich existiert auch eine orthorhombische Modifikation von Pyrochroit und es liegen Angaben über die Synthese einer orthorhombischen Modifikation vor2).

ASTER data have been widely and successfully used in lithological mapping and mineral exploration for decades. The errors due to atmospheric water vapor and the characteristics of the photoelectric sensor could lead to the anomalous characteristics of band 5 and 9 in the ASTER standard reflectivity product. These anomalies could result in the spectroscopic misidentification of minerals. This study proposed a simple method of atmospheric correction for converting radiance-at-sensor to ground reflectance. The ASTER VNIR/SWIR reflectance correction factor was derived to correct the spectral shape bias resulting from the radiometric calibration error using airborne hyperspectral CASI_SASI data. The ASTER VNIR/SWIR reflectance correction factor was derived to correct the spectral shape bias resulting from the radiometric calibration error. After applying the reflectance factor to the atmospheric-corrected ASTER L1B data, a band combination mapping method was proposed for identifying minerals more quickly and accurately. The results indicate that this method for atmospheric correction of ASTER data produces very good results in the arid and bare areas. It is still unknown whether the method is suitable for humid and rainy areas where atmospheric water vapor varies spatially more than in arid and bare areas. After applying the reflectance factor to the atmospheric-corrected ASTER L1B data, the mean error of all reflectance bands decreased from 0.0256 to 0.002, and the standard deviation decreased from 0.04251 to 0.0007. The errors of the 2/1, 5/6 and 9/8 band ratios decreased from 2.38%, 4.102%, and 4.28% to 1.26%, 0.162%, and 0.31%, respectively. The radiometric calibration error of the ASTER band 1 9 data can lead to the overestimation of kaolinite. A band index of 2/1 for retrieving Fe3+ cannot produce a reliable Fe3+ distribution map, and a new index should be developed.

The Center for the Study of Earth from Space (CSES) at the University of Colorado, Boulder, has developed a prototype interactive software system called the ‘‘Spectral Image Processing System (SIPS)’’ using ‘‘IDL’’ (the Interactive Data Language) on UNIX‐based workstations. SIPS is designed to take advantage of the combination of high spectral resolution and spatial data presentation unique to imaging spectrometers. It streamlines analysis of these data by allowing scientists to interact with entire datasets in real‐time. SIPS provides visualization tools for rapid exploratory analysis and numerical tools for quantitative modeling. The user interface is X‐windows‐based, user friendly, and provides ‘‘point and click’’ operation. SIPS is being used for multidisciplinary research concentrating on the use of physically‐based analysis methods to enhance scientific results from imging spectrometer data. The objective of this continuing effort is to develop operational techniques for quantitative analysis of imaging spectrometer data and to make them available to the scientific community prior to the launch of imaging spectrometer satellite systems such as the Earth Observing System (EOS) High Resolution Imaging Spectrometer (HIRIS).