Magnetic Minerals In Sediments Research Articles

Environmental magnetic records derived from lacustrine sediments in the Western Guangdong Province, China: Implications for Late-Holocene climatic/environmental changes

The western Guangdong Province (WGDP) in China, influenced by both the East Asian and the Indian summer monsoon, is a pivotal region for exploring the Asian summer monsoon (ASM) evolution. So far, there still lacks detail studies on late Holocene climatic/environmental changes here. In this study, multiple magnetic parameters were measured on the lake sediments of Hedong section in this area. Results indicated a dominance of pseudo-single-domain detrital (titano-)magnetite or maghemite mixed with paramagnetic and anti-ferromagnetic minerals in sediments, and the impacts of authigenic greigite, bacterial activity, post-depositional dissolution, and dilution effects were trivial. Changes in rainfall-induced surface erosion intensity were determined as a role in sediment magnetic properties. Intensified surface erosion deduced by increased rainfall favored enhanced concentrations and more coarse-grained magnetic minerals in sediments, and vice versa. Thus, the magnetic parameters can be used to reflect varying ASM strength in the past ~4300 years. They revealed four relatively humid (strengthened ASM) (i.e., 4300–4000 cal. yr BP, 3500–3130 cal. yr BP, 2640–1950 cal. yr BP, and 1250–850 cal. yr BP), and three dry periods (weakened ASM) (i.e., 4000–3500 cal. yr BP, 3130–2640 cal. yr BP, and 1950–1250 cal. yr BP) which coincided with the Bond events 3, 2, and 1 respectively. In combination with the three significant cycles (i.e., 1250-, 75-, and 65-year) revealed by spectral analysis on SIRM record, we inferred both the external forcing (e.g., solar activity) and internal hemispheric-scale atmospheric processes (e.g., ENSO, North Atlantic Oscillation) have played an integral role in late Holocene climate changes in the study region.

Environmental Magnetic Characteristics and Heavy Metal Pollution Assessment of Sediments in the Le’an River, China

Environmental magnetism parameters have become a useful tool in addressing environmental issues. Due to the rapid, sensitive, economical and non-destructive characteristics of environmental magnetism, the present contribution focuses on magnetism parameters as proxy for heavy metal pollution, especially from their relationship with contents of heavy metal. We evaluated heavy metals pollution and examined environmental magnetism in the Dexing section of the Le’an River. The pollution load index (PLI) of Cr, Pb, As, Cu and Zn, as well as the concentration of other heavy metals, were analyzed, and the magnetic indexes of various sediments were analyzed. The results showed that the concentrations of all heavy metals far exceeded the local background values, and that the average contamination factor of Cu was as high as 22.88, making it the element of most serious contamination. The problem of heavy metal pollution near the mine is very serious. The content of magnetic minerals in sediments of Le’an River is relatively high and the composition of magnetic minerals is relatively stable. The stable-single domin (SSD) content is high at S1 and S10, indicating that ferromagnetic mineral content is relatively rich here, which dominates the magnetic characteristics of the sample. In general, it was found that environmental magnetism indicators did not exist in the Dexing section of the Le’an River that could clearly indicate the concentration of heavy metal pollution. Only a few heavy metals can be effectively indicated by magnetic parameters. IRM-20mT and S-ratio can be used as indicators of Cr, Pb, As, Cu and Zn, but they are not accurate. The correlation between Sr and magnetic indexes IRM200mT, IRM300mT, SIRM, IRM-300mT and HIRM is significant, which can be used as an indicator of Sr concentration. IRM20mT can also be used as an indicator of Hg concentration.

Variation in humidity and the forcing mechanism in Asian monsoon-influenced regions indicated by hematite/goethite from Baxian Lake, southern China, since AD 800

Understanding the potential mechanisms driving the precipitation pattern in the Asian summer monsoon (ASM) area is significant to reconstructing the environmental and hydrological conditions over the past 2000 years. However, robust and consistent conclusions have been hampered by the complex processes controlling the dynamics and diverse interconnected linkage of the Asian monsoon. Here, we present a reconstruction of variations in humidity since AD 800, based on the ratio of hematite to goethite (Hem/Goe) and other magnetic parameters in the sediments of Baxian Lake, southern China. The record indicates that a dramatic transition from dry to humid climate occurred during AD 800–950 and then returned to extreme drought during the second half of the Medieval Warm Period. The fluctuations between a relatively wet climate and weak drought were also demonstrated during the Little Ice Age (AD 1450–1800). Climate-influenced vegetation coverage may influence the flux of weathered detrital magnetic minerals in sediments, as it hinders the input of coarser detritus into Baxian Lake. The magnetic minerals in the sediments were not significantly altered during the post-depositional processes. Additionally, the Hem/Goe record indicates that an opposite precipitation pattern occurred in southern China when compared with precipitation records in northern China and India. We ascribe this result to the superimposition of land-ocean-atmosphere dynamics on the traditional model of the intertropical convergence zone (ITCZ) movement forced by the Atlantic Meridional Overturning Circulation. This is significant for enhancing our understanding of the relationship among the continent-ocean thermal gradient, ASM variation, ITCZ movement, El Niño Southern Oscillation-like events, and extreme climates in areas influenced by the ASM.

Magnetic properties of the surface sediments from the Huguangyan Maar Lake in tropical Southern China and the sediment source identification

ABSTRACTDeciphering the source(s) of sediment deposited in Hugunagyan Lake in South China using magnetic properties will advance our understanding of the evolution of East Asian monsoon systems. However, the source of magnetic minerals in the surface sediments of this lake is unknown, still needing further exploration. Due to simple hydrological systems, the Hugunagyan Lake provides a unique record for investigating the magnetic property of sediments and surface processes. In this study, based on the magnetic properties of 43 surface sediment, 12 surface soil, and 7 volcanic rock samples from the catchment, we demonstrate that the magnetic minerals in sediments were dominated by fine super paramagnetic magnetic particles, with coexistence of pseudo‐single‐domain states minerals. There are no signatures showing the presence of biogenic and authigenic magnetite. The magnetic properties of surface sediments display significant differences between the potential sources of aeolian dust from the loess in North China and modern surface soils in Central Asia, suggesting that the magnetic minerals mainly originate from the weathered materials in the catchment, and there are no further signals of winter monsoon‐driven aeolian dust input.

Indian summer monsoon variability over last 2000 years inferred from sediment magnetic characteristics in Lugu Lake, southwest China

Knowledge of climatic change during the past 2000 years in southwestern China is important for understanding the evolution of the Indian summer monsoon (ISM). For this study, we conducted systematic analysis of magnetic minerals in sediments from Lugu Lake in northwestern Yunnan Province. Magnetic measurements suggest that magnetite dominated the studied magnetic mineral assemblages. Both natural origins and anthropogenic activities are considered to be the sources of the magnetic minerals based on the correlations of χ vs. χfd% and χARM/χ. The magnetic minerals of natural origins can be attributed to terrestrial detrital input rather than biogenic sources. Combined with diatom and geochemical records, magnetic parameters including χ, χfd%, and S-ratio can be used as sensitive indicators of ISM change, and suggest that two significant dry periods occurred in the Medieval Warm Period (MWP, 800–1300 CE) and Roman Warm Period (RWP, 0–400 CE) and two relatively wet intervals in the Dark Ages Cold Period (DACP, 400–800 CE) and Little Ice Age (LIA, 1300–1850 CE). Significant shifts of magnetic parameters in Lugu Lake samples revealed sensitivity to precipitation-controlled catchment erosion. The climatic patterns shown by the magnetic characteristics were generally similar to those in extensive areas dominated by the ISM. We speculate that rainfall caused by the ISM during the last 2000 years may be related to the variations of El Niño/Southern Oscillation (ENSO) and the mean position migration of the ITCZ.

Magnetic properties indicate the sources of hadal sediments in the Yap Trench, northwest Pacific Ocean

Magnetic minerals in marine sediments are often masked by the primary natural remanent magnetization and material source signals. In order to understand sedimentary environment and sources of sediments in the abyss, we studied 126 samples of five bottom surface cores collected by the Jiaolong Submersible at 4000–7000 m in depth during the third stage of the China’s 38th Ocean Voyage. The magnetic properties of the sediments were analyzed using Thermosusceptibility (k-T) curves and Day plot. The results show that the magnetic minerals in the sediments of the Yap Trench are mainly maghemite, and the overall magnetic and soft magnetic properties were strong. The magnetic particles of sediments are dominated by pseudo single domains (PSD) grains. The main source of sediment is locally-derived basalt debris and volcanic debris, and the process of sedimentation is gravity-like flow deposition.

Recent Applications of Mineral Magnetic Methods in Sediment Pollution Studies: a Review

This paper reviews recent progress in applying mineral magnetic methods in sediment pollution studies. Such applications include its use as a dating marker, as a proxy for heavy metal concentrations and to trace metal pollutant dispersal. The mineral magnetic method has been found to be a promising tool in a wide range of sediment metal pollution studies. However, its use as a proxy of heavy metal concentrations is not always straightforward. This reflects the potentially mixed origins of magnetic minerals in sediments which may have an anthropogenic, natural or mixed source. Furthermore, anthropogenic magnetic particles may not have a common source with heavy metals. The possible linkage between magnetic minerals and heavy metals is discussed. The role of sorting, sorption/desorption and post-depositional diagenesis on the magnetic mineral-heavy metal linkage is highlighted as still requiring careful consideration. It is suggested that detailed characterisation of magnetic mineralogy using combined magnetic, geochemical and mineralogical methods is critical to the optimization of sediment pollution studies using a mineral magnetic approach.

Identification of the thick-layer greigite in sediments of the South Yellow Sea and its geological significances

Magnetic minerals in sediments of the continental shelf are sensitive to environmental changes. Therefore, to determine the exact phases of magnetic minerals is the prerequisite to investigate the paleoenvironmental significances. In this study, a comprehensive rock magnetic investigation, coupled with mineralogical studies, was carried out on the long core NHH01 (with a length of 125.64 m) from the central continental shelf of the South Yellow Sea. Single-domain greigite was identified as the dominant magnetic carrier in sediments between 44.90 and 51.80 m, and terrigenous magnetite is the major magnetic phase in the adjacent layers. The existence of greigite unambiguously indicates an anoxic environment. We tentatively interpreted that such an environment could be formed by the fast sea level changes, long-existing of the cold eddies during warm stages, or in a lake which might be related to locally tectonic uplifting. Therefore, the occurrence of the thick-layer greigite could supply a new perspective to paleoenvironmental or even tectonic studies.

VARIFORC: An optimized protocol for calculating non-regular first-order reversal curve (FORC) diagrams

High-resolution first-order reversal curve (FORC) diagrams are increasingly employed to characterize magnetic minerals in sediments, and especially as a magnetofossil detection tool. Conventional processing protocols, however, are not well suited for this purpose because the opposed needs of high resolution and smoothing of noisy data over different regions of the FORC diagram cannot be reconciled. This problem is particularly severe in samples containing non-interacting single-domain particles, whose FORC signature is described by an infinitely narrow, divergent feature called a central ridge. In this paper, a new FORC processing protocol called VARIFORC (VARIable FORC smoothing) is presented for the analysis of non-regular FORC functions, such as those featuring a central ridge. This protocol is based on weighted polynomial regression of rectangular arrays of measurement points whose size is determined by the local properties of the FORC function (i.e. small arrays where high resolution is needed and vice-versa). The resulting FORC diagram is characterized by improved signal-to-noise ratios that pass significance tests over much larger domains. This enables simultaneous quantitative analysis of FORC signatures corresponding to different magnetization processes (e.g. the central ridge produced by single-domain particles and a weak, extended background due to detrital magnetic minerals). VARIFORC has been successfully tested on a magnetofossil-bearing pelagic carbonate sample that has a non-regular FORC function, and on a volcanic ash sample with a typical pseudo-single-domain signature. An unexpected minor central ridge contribution, which is invisible to traditional processing, has been detected in the volcanic ash sample. This finding demonstrates the effectiveness of the new FORC processing protocol and potential new applications of high-resolution FORC measurements.

Magnetic minerals in sediments at the Cretaceous/Paleogene boundary (the Gams Section, Eastern Alps)

The paper presents results of detailed magnetomineralogical and microprobe studies of sediments at the Cretaceous/Paleogene (K/T) boundary in two epicontinental sections in the Eastern Alps (Austria), where deposits, including the K/T boundary, outcrop along the Gams River and its tributaries. K/T boundary layers in these sections are similar in the set of such magnetic minerals as iron hydroxides, ferrospinels, hemoilmenite, titanomagnetite, magnetite, hematite, and metallic iron. However, the boundary layer in the Gams-1 section is distinguished by the presence of metallic nickel and its alloy with iron and by the absence of iron sulfides, whereas nickel has not been discovered in the Gams-2 section, which, however, contains iron sulfides of the pyrite type. Therefore, these minerals occur locally. It is suggested that enrichment in iron hydroxides of a com- mon origin can be regarded as a global phenomenon inherent in the K/T boundary and unrelated to an impact event.

Sources of fine-grained magnetic minerals in sediments: a problem revisited

Progress in the discrimination of fine-grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized. The former measurements yield values for low field and frequency-dependent susceptibility (χlfand χfd, respectively). The latter generate an Anhysteretic Remanent Magnetisation (ARM) that, when normalized to the DC bias field, can be represented as the susceptibility of ARM (χARM). Using quotients derived from χlf, χfdand χARMto generate bi-logarithmic plots, it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments. Sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil-derived and magnetosome-derived assemblages. Fire also appears to give rise to a distinctive envelope of values indicative of smaller magnetic grain sizes, whilst the signature of extracellular magnetite is indicative of the finest grain sizes here recorded.

Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore of Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process

In this paper, we present the results of down core variations in magnetic susceptibility and magnetic mineral composition of fifteen piston cores retrieved from the active continental margin offshore of southwestern Taiwan, where a wide distribution of bottom simulating reflectors (BSRs) related to gas hydrate layers has been detected. X-ray analysis on magnetic extracts from the cores indicates that detrital magnetite and authigenic greigite, in various proportions, are the dominant magnetic minerals in sediments. Non-magnetic, authigenic pyrite is generally associated with greigite, but it may co-exist with magnetite or may solely occur in sediments. Consequently, the sediment sequences of the fifteen piston cores have complicated magnetic mineral assemblages that result in various magnetic susceptibility profiles. For core segments containing detrital magnetite as the only magnetic mineral, values of magnetic susceptibility are moderate with small variations (8-15×10^(-6) SI), which can be regarded as the susceptibility backgrounds for the initially deposited sediments. However, high magnetic susceptibilities relative to the backgrounds were found in core segments where magnetic mineral is enriched in greigite. Magnetic susceptibilities lower than the backgrounds were found in segments where neither magnetite nor greigite were detected. The complicated occurrence of magnetic minerals reveals that their host sediments at different levels have suffered various degrees of early diagenetic process ranging from oxic to anoxic conditions. Due to very low sedimentary organic matter content in the study area, detrital magnetite persisted in sediments that were subjected to initially oxic (or sub-oxic) conditions. However, the sedimentary organic matter is apparently insufficient for providing reducing environments for the formation or enrichment of authigenic iron sulfides. Instead, we propose that gaseous methane derived from gas hydrates in deeper sedimentary layers should be the most likely source of extra organic matter. The different flux intensities of this gas either through slow diffusion or rapid venting resulted in various anoxic conditions, which caused the dissolution or survival of magnetite and the formation or enrichment of greigite and pyrite.

Biomineralization of magnetic minerals

New developments and discoveries in biomineralization have occurred almost continuously in the intervening decade since the previous IUGG quadrennial report on biomineralization and biomagnetism was published [Kirschvink, 1983]. Biomineralization is widespread in the biosphere and over 60 different inorganic minerals are produced by a variety of organisms from bacteria to humans [Lowenstam and Weiner, 1989]. The literature on biomineralization is interdisplinary, combining research in microbiology, biotechnology, physics, geology, and paleomagnetism. For paleomagnetism and rock magnetism, iron biomineralization of magnetic minerals is of prime importance. From a paleomagnetism perspective, biogenic magnetic minerals can be deposited in sediments and acquire a natural remanent magnetization that preserves a record of the ancient geomagnetic field. From a rock magnetism perspective, biogenic magnetic minerals provide novel sources of magnetic material for experimental studies in fine particle magnetism. Both perspectives are interrelated through a common goal of developing magnetic techniques to detect biogenic magnetic minerals in sediments and soils. For example, the extent to which iron biominerals contribute to the fine‐grained magnetic mineral assemblages in freshwater and marine sediments is important for identifying and interpreting the magnetic record of environmental change [Oldfield, 1992; Reynolds and King, this issue].

An investigation into the source of magnetic minerals in some Finnish lake sediments

The source of magnetic minerals in the sediments of five Finnish lakes, which carry a palaeomagnetic record of the geomagnetic field, was found to be primary magnetite in the glacial drift of the catchments. The magnetite is concentrated in the central lake sediments. The ratio of haematite to magnetite was found to decrease in the progression drift-stream bedload-lake sediment. A consistent, temporal decrease of magnetic mineral concentration was found in all the lake sediments studied and is related to maturation of the soils and vegetation surrounding the lakes. This distinctive trend contrasts with that seen in Britain and is discussed in terms of man's influence on landscape development.