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Qingsong Liu - One of the best experts on this subject based on the ideXlab platform.
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An integrated natural Remanent Magnetization acquisition model for the Matuyama-Brunhes reversal recorded by the Chinese loess
'Wiley', 2018Co-Authors: Jin Chunsheng, Qingsong Liu, Hu Pengxiang, Jiang Zhaoxia, Li C, Han Peng, Yang Huihui, Liang WentianAbstract:Geomagnetic polarity reversal boundaries are key isochronous chronological controls for the long Chinese loess sequences, and further facilitate paleoclimatic correlation between Chinese loess and marine sediments. However, owing to complexity of postdepositional Remanent Magnetization (pDRM) acquisition processes related to variable dust sedimentary environments on the Chinese Loess Plateau (CLP), there is a long-standing dispute concerning the downward shift of the pDRM recorded in Chinese loess. In this study, after careful stratigraphic correlation of representative climatic tie points and the Matuyama-Brunhes boundaries (MBB) in the Xifeng, Luochuan, and Mangshan loess sections with different pedogenic environments, the downward shift of the pDRM is semiquantitatively estimated and the acquisition model for the loess natural Remanent Magnetization (NRM) is discussed. The measured MB transition zone has been affected by the surficial mixing layer (SML) and reMagnetization. Paleoprecipitation is suggested to be the dominant factor controlling the pDRM acquisition processes. Rainfall-controlled leaching would restrict the efficiency of the characterized Remanent Magnetization carriers aligning along the ancient geomagnetic field. We conclude that the MBB in the central CLP with moderate paleoprecipitation could be considered as an isochronous chronological control after moderate upward adjustment. A convincing case can then be made to correlate L8/S8 to MIS 18/1
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acquisition of chemical Remanent Magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds
Earth and Planetary Science Letters, 2015Co-Authors: Zhaoxia Jiang, Qingsong Liu, Mark J Dekkers, Lisa Tauxe, Huafeng Qin, Vidal Barron, Jose TorrentAbstract:Hematite-bearing red beds are renowned for their chemical Remanent Magnetization (CRM). If the CRM was acquired substantially later than the sediment was formed, this severely compromises paleomagnetic records. To improve our interpretation of the natural Remanent Magnetization, the intricacies of the CRM acquisition process must be understood. Here, we contribute to this issue by synthesizing hematite under controlled 'Earth-like' field conditions (≲100 μT). CRM was imparted in 90 oriented samples with varying inclinations. The final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides. When the magnetic field intensity is ≳40 μT, the CRM records the field direction faithfully. However, for field intensities ≲40 μT, the CRM direction may deviate considerably from that of the applied field during synthesis. The CRM intensity normalized by the isothermal Remanent Magnetization (CRM/IRM@2.5 T) increases linearly with the intensity of growth field, implying that CRM could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties. CRM in hematite has a distributed unblocking temperature spectrum from ~200 to ~650 °C, while hematite with a depositional Remanent Magnetization (DRM) has a more confined spectrum from ~600to680°C because it is usually coarser-grained and more stoichiometric. Therefore, the thermal decay curves of CRM with their concave shape are notably different from their DRM counterparts which are convex. These differences together are suggested to be a potential discriminator of CRM from DRM carried by hematite in natural red beds, and of significance for the interpretation of paleomagnetic studies on red beds.
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Reliability of the natural Remanent Magnetization recorded in Chinese loess
Journal of Geophysical Research, 2010Co-Authors: Chunsheng Jin, Qingsong LiuAbstract:[1] Chinese loess-paleosol sequences undoubtedly have recorded geomagnetic events (both polarity reversals and excursions). However, the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain. To test the reliability and consistency of the natural Remanent Magnetization records in Chinese loess, 10 subsets of parallel samples across the Matuyama-Brunhes (MB) reversal boundary were obtained from the Luochuan region in the hinterland of the Chinese Loess Plateau. Our paleomagnetic results show diversified virtual geomagnetic poles (VGPs) during the MB transition but consistent VGPs outside of the transitional zone. The anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed. The discrepancies of the characteristic Remanent Magnetization within the MB transition are probably due to the low efficiency in aligning magnetic grains, mainly pseudo-single-domain magnetite, associated with the low field intensity. Nevertheless, the stratigraphic location of the MB boundary can be confidently defined. Therefore, we conclude that Chinese loess-paleosol sequences can record geomagnetic reversal events, but the morphology within the polarity transition is rather questionable.
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Chemical overprint on the natural Remanent Magnetization of a subtropical red soil sequence in the Bose Basin, southern China
Geophysical Research Letters, 2007Co-Authors: Chenglong Deng, Qingsong Liu, Wei Wang, Caicai LiuAbstract:[1] We present a high-resolution paleomagnetic investigation of the subtropical red soil sequence at the Damei section, Bose Basin, southern China. Maghemite with low coercivities and fine-grained hematite with high coercivities but relatively low unblocking temperatures were identified as main carriers of the natural Remanent Magnetization (NRM). Strong chemical weathering occurring under subtropical climatic conditions in southern China led to a chemical Remanent Magnetization (CRM) overprint that is sufficiently strong to mask the primary NRM. Analysis of the Bose Basin soil sequence indicates that the CRM has a large lock-in depth (>4 m). This example shows that magnetostratigraphic studies on red soil sequences in subtropical-tropical southern China should be interpreted with caution.
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partial anhysteretic Remanent Magnetization parm of synthetic single and multidomain magnetites and its paleoenvironmental significance
Chinese Science Bulletin, 2005Co-Authors: Qingsong Liu, Yongxin Pan, Rixiang Zhu, Xixi ZhaoAbstract:In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few parameters using partial anhysteretic Remanent Magnetization (pARM). Because MD fraction contains only soft (easy to be demagnetized) coercivity spectrum, pARM(>20 mT) was sensitive in eliminating MD contributions. Ratio of pARM(5 mT, 10 mT)/pARM(0, 5 mT) is useful in quantifying a relative abundance of mass ratio between SD and MD fractions. These new proxies can quickly characterize the details of grain size distribution of magnetic minerals in paleoclimatic and paleomagnetic studies.
Guillaume Dupont-nivet - One of the best experts on this subject based on the ideXlab platform.
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Challenges in isolating primary Remanent Magnetization from Tethyan carbonate rocks on the Tibetan Plateau: Insight from remagnetized Upper Triassic limestones in the eastern Qiangtang block
Earth and Planetary Science Letters, 2019Co-Authors: Wentao Huang, Michael Jackson, Mark Dekkers, Yang Zhang, Bo Zhang, Zhaojie Guo, Guillaume Dupont-nivetAbstract:Carbonate rocks, widely used for paleomagnetically quantifying the drift history of the Gondwana-derived continental blocks of the Tibetan Plateau and evolution of the Paleo/Meso/Neo-Tethys Oceans, are prone to pervasive reMagnetization. Identifying reMagnetization is difficult because it is commonly undetectable through the classic paleomagnetic field tests. Here we apply comprehensive paleomagnetic, rock magnetic, and petrographic studies to upper Triassic limestones in the eastern Qiangtang block. Our results reveal that detrital/biogenic magnetite, which may carry the primary natural Remanent Magnetization (NRM), is rarely preserved in these rocks. In contrast, authigenic magnetite and hematite pseudomorphs after pyrite, and monoclinic pyrrhotite record three episodes of reMagnetization. The earliest reMagnetization was induced by oxidation of early diagenetic pyrite to magnetite, probably related to the collision between the northeastern Tibetan Plateau and the Qiangtang block after closure of the Paleo-Tethys Ocean in the Late Triassic. The second reMagnetization, residing in hematite and minor goethite, which is the further subsurface oxidation product of pyrite/magnetite, is possibly related to the development of the localized Cenozoic basins soon after India-Asia collision in the Paleocene. The youngest reMagnetization is a combination of thermoviscous and chemical Remanent Magnetization carried by authigenic magnetite and pyrrhotite, respectively. Our analyses suggest that a high supply of organic carbon during carbonate deposition, prevailing sulfate reducing conditions during early diagenesis, and widespread orogenic fluid migration related to crustal shortening during later diagenesis, have altered the primary remanence of the shallow-water Tethyan carbonate rocks of the Tibetan Plateau. We emphasize that all paleomagnetic results from these rocks must be carefully examined for reMagnetization before being used for paleogeographic reconstructions. Future paleomagnetic investigations of the carbonate rocks in orogenic belts should be accompanied by thorough rock magnetic and petrographic studies to determine the origin of the NRM.
Ramon Egli - One of the best experts on this subject based on the ideXlab platform.
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magnetotaxis and acquisition of detrital Remanent Magnetization by magnetotactic bacteria in natural sediment first experimental results and theory
Geochemistry Geophysics Geosystems, 2014Co-Authors: Xuegang Mao, Ramon Egli, Nikolai Petersen, Marianne Hanzlik, Xiangyu ZhaoAbstract:[1] The widespread occurrence of magnetotactic bacteria (MTB) in several types of marine and freshwater sediment, and the role of fossil magnetosomes (magnetofossils) as main Remanent Magnetization carriers therein, has important paleomagnetic and paleoenvironmental implications. Despite numerous studies on MTB biology and on magnetofossil preservation in geological records, no detailed information is yet available on how magnetotaxis (i.e., the ability to navigate along magnetic field lines) is performed in sedimentary environments, and on how magnetofossils possibly record the Earth magnetic field. We provide for the first time experimental evidence for these processes. MTB living in sediment are poorly aligned with the geomagnetic field, contrary to what is observed in water. This can explain the seemingly excessive magnetic moment of most MTB. The observed alignment is sufficient for supporting magnetotaxis across the typical thickness of chemical gradients. Experiments with magnetofossil-rich sediment suggest that a natural Remanent Magnetization (NRM) is acquired by magnetofossils in the so-called benthic mixed layer, where natural MTB populations usually occur. The acquired NRM is proportional to the applied field at least up to ∼160 µT, and its intensity is compatible with values observed in nature for same sediment types. Therefore, if fossil magnetosome chains are not subjected to further alteration by early diagenetic processes, they can provide useful relative paleointensities. We propose a preliminary model to explain early stages of magnetofossil NRM acquisition as the result of a dynamic equilibrium between magnetic torques and randomizing forces due to sediment mixing.
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theoretical considerations on the anhysteretic Remanent Magnetization of interacting particles with uniaxial anisotropy
Journal of Geophysical Research, 2006Co-Authors: Ramon EgliAbstract:[1] The anhysteretic Remanent Magnetization (ARM) is widely used in rock magnetism and paleomagnetism because of its sensitivity to the domain state of magnetic particles and the close analogy to natural Remanent Magnetizations. On the other hand, the ARM shares with other weak-field Magnetizations the property of being extremely sensitive to magnetostatic interactions. Therefore it is desirable to model the effects of interactions on natural assemblages of magnetic particles. Direct micromagnetic calculations of the ARM acquisition process are not practicable; therefore an analytical approach is used calculate the ARM susceptibility of a system of interacting single-domain (SD) particles. The model is based on a statistical description of the interaction field. The equations obtained have been used to evaluate the dependence of the ARM on the packing fraction of the magnetic particles. The effect of interactions on the anisotropy of ARM (AARM) was evaluated as well. The AARM of densely packed particles is complex and depends critically on the microcoercivity. A physical interpretation of the AARM of highly interacting particles is therefore difficult.
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analysis of the field dependence of Remanent Magnetization curves
Journal of Geophysical Research, 2003Co-Authors: Ramon EgliAbstract:[1] A new method to calculate and analyze coercivity distributions of measured acquisition/deMagnetization curves of Remanent Magnetization is presented. The acquisition/deMagnetization curves are linearized by rescaling both the field and the Magnetization axes. An appropriate filtering of the linearized curves efficiently removes measurement errors prior to evaluating the coercivity distributions. The filtered coercivity distributions are modeled using a set of generalized probability density functions in order to estimate the contributions of different magnetic components. An error estimation is calculated for these functions with analytical and numerical methods in order to evaluate whether the model is significantly different from the measured data. Three sediment samples from Baldeggersee (Switzerland) and three samples of urban atmospheric particulate matter (PM) have been analyzed using this method. It is found that the coercivity distributions of some of the magnetic components show significant and consistent deviations from a logarithmic Gaussian function. Large deviations are found also in the coercivity distributions of theoretical AF deMagnetization curves of single-domain and multidomain particles. Constraints in the shape of model functions affect the identification and quantification of magnetic components from Remanent Magnetization curves and should be avoided as far as possible. The generalized probability density function presented in this paper is suitable for appropriate modeling of Gaussian and a large number of non-Gaussian coercivity distributions.
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anhysteretic Remanent Magnetization of fine magnetic particles
Journal of Geophysical Research, 2002Co-Authors: Ramon Egli, W LowrieAbstract:[1] Various magnetic parameters are in common use for estimating the grain size of magnetic particles. Among these, the ratio of the intensity of anhysteretic Remanent Magnetization (ARM) to that of isothermal Remanent Magnetization, as well as their alternating field (AF) deMagnetization curves are used as an indicator of the domain state of the particles. Several models have been proposed to describe physically the acquisition of ARM in a biased AF field. Jaep [1969] first developed a semiquantitative theory based entirely on the thermal fluctuation analysis developed by Neel [1949, 1954, 1955]. Significant discrepancies were found between his model and experimental results on magnetite. A new, general theory of ARM based on the work of Jaep is presented here, with particular regard to the influence of various parameters like grain size, coercivity, and mineralogy on ARM intensity. An analytical expression for ARM intensity in the special case of very fine particles was derived from this theory, and a good agreement with experimental results and data from the literature was found. A new estimation of the atomic reorganization time was obtained from ARM measurements on a sample of the Yucca Mountain Tuff, which has well-known mineralogy and grain-size distribution. The results are in agreement with the value proposed by McNab et al. [1968] for magnetite. Some authors considered magnetic interactions as the key to understand the ARM in fine particles, and this is certainly true for strongly interacting samples. In this case, ARM would be useless for the characterization of magnetic grains. However, many sediments have a very low concentration of well-distributed magnetic grains. For these samples, the explanation of an ARM in terms of intrinsic properties of the grains, as qualitatively proposed by other authors, is more suitable.
I H M Van Oorschot - One of the best experts on this subject based on the ideXlab platform.
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analysis of isothermal Remanent Magnetization acquisition curves using the expectation maximization algorithm
Geophysical Journal International, 2002Co-Authors: David Heslop, Mark J Dekkers, Pauline P Kruiver, I H M Van OorschotAbstract:SUMMARY The acquisition of isothermal Remanent Magnetization (IRM) curves through the application of stepwise-increasing uniaxial fields to a rock-magnetic sample provides an important non-destructive tool for the investigation of coercivity spectra (Dunlop
Wentao Huang - One of the best experts on this subject based on the ideXlab platform.
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Challenges in isolating primary Remanent Magnetization from Tethyan carbonate rocks on the Tibetan Plateau: Insight from remagnetized Upper Triassic limestones in the eastern Qiangtang block
Earth and Planetary Science Letters, 2019Co-Authors: Wentao Huang, Michael Jackson, Mark Dekkers, Yang Zhang, Bo Zhang, Zhaojie Guo, Guillaume Dupont-nivetAbstract:Carbonate rocks, widely used for paleomagnetically quantifying the drift history of the Gondwana-derived continental blocks of the Tibetan Plateau and evolution of the Paleo/Meso/Neo-Tethys Oceans, are prone to pervasive reMagnetization. Identifying reMagnetization is difficult because it is commonly undetectable through the classic paleomagnetic field tests. Here we apply comprehensive paleomagnetic, rock magnetic, and petrographic studies to upper Triassic limestones in the eastern Qiangtang block. Our results reveal that detrital/biogenic magnetite, which may carry the primary natural Remanent Magnetization (NRM), is rarely preserved in these rocks. In contrast, authigenic magnetite and hematite pseudomorphs after pyrite, and monoclinic pyrrhotite record three episodes of reMagnetization. The earliest reMagnetization was induced by oxidation of early diagenetic pyrite to magnetite, probably related to the collision between the northeastern Tibetan Plateau and the Qiangtang block after closure of the Paleo-Tethys Ocean in the Late Triassic. The second reMagnetization, residing in hematite and minor goethite, which is the further subsurface oxidation product of pyrite/magnetite, is possibly related to the development of the localized Cenozoic basins soon after India-Asia collision in the Paleocene. The youngest reMagnetization is a combination of thermoviscous and chemical Remanent Magnetization carried by authigenic magnetite and pyrrhotite, respectively. Our analyses suggest that a high supply of organic carbon during carbonate deposition, prevailing sulfate reducing conditions during early diagenesis, and widespread orogenic fluid migration related to crustal shortening during later diagenesis, have altered the primary remanence of the shallow-water Tethyan carbonate rocks of the Tibetan Plateau. We emphasize that all paleomagnetic results from these rocks must be carefully examined for reMagnetization before being used for paleogeographic reconstructions. Future paleomagnetic investigations of the carbonate rocks in orogenic belts should be accompanied by thorough rock magnetic and petrographic studies to determine the origin of the NRM.
