Detailed rock magnetic studies of 55 lavas from Yixian and Fuxin area, West Liaoning, show the primary carriers of remanence to be pseudo-single domain ti-tanomagnetite. K/Ar dating indicates that the volcanic sequenc...Detailed rock magnetic studies of 55 lavas from Yixian and Fuxin area, West Liaoning, show the primary carriers of remanence to be pseudo-single domain ti-tanomagnetite. K/Ar dating indicates that the volcanic sequence spans 93 to 133 Ma. Stepwise thermal demagnetization successfully isolated well-defined characteristic magnetization (ChRM) in all lavas thermal-treated above 250℃ The mean paleodirections are D/I=5.9°/58.8° (α95 = 2.9°) and D/I =179.2°/-59.9° (α95 = 5.2°) for 27 normally magnetized flows and 28 reversibly magnetized flows, respectively. It indicates that since the Early Cretaceous there is no significant horizontal movement and rotation between the Yixian-Fuxin area and Eurasia. However, Korea Peninsula may have undergone a clockwise rotation of 33.9° relative to the Yixian-Fuxin area during the Cretaceous. On the basis of characteristics of hotspot origins (core-mantle boundary or upper mantle), the clockwise rotation of Korea Peninsula relative to Eurasia is assumed to be展开更多
A detailed record of the Matuyama-Brunhes (M-B) transition has been obtained from the loess unit 8 (L8) at Duanjiapo (34.2° N, 109.2° E), Shannxi Province of China. An investigation of the rock magnetic prop...A detailed record of the Matuyama-Brunhes (M-B) transition has been obtained from the loess unit 8 (L8) at Duanjiapo (34.2° N, 109.2° E), Shannxi Province of China. An investigation of the rock magnetic properties using hysteresis loops, thermomagnetic analyses identifies pseudo-single domain magnetite as the main carrier of the rema-nence, with a small contribution from maghemite and hema-tite. The paleo-direction records obtained reveal: ( i ) The M-B transition was recorded in the middle and lower part of L8, and comprises of five fast reversals. (ii) The duration of the M-B polarity transition related to the directional change is about 4800 a. (iii) The virtual geomagnetic pole (VGP) path during the transition is confined over Africa, peaked 90° away from the sampling site, in contrast with the results obtained from the Weinan loess section. The different VGPs are probably attributed to the pedogenesis.展开更多
Rock-magnetic and palaeomagnetic studies have been carried out on the interval of famous fossil-bearing sedimentary rocks and its overlying basalts and underlying basalts at the Sihetun section, West Liaoning Province...Rock-magnetic and palaeomagnetic studies have been carried out on the interval of famous fossil-bearing sedimentary rocks and its overlying basalts and underlying basalts at the Sihetun section, West Liaoning Province. Normal polarity was obtained for the sedimentary interval and the underlying basalts, while reversed polarity was found in the overlying basalts. Taking account of the new 40Ar/39Ar ages (Swisher et al., 1999), we classified the fossil-bearing sedimentary interval into the Barremian M3n zone (Early Cretaceous age). Several abnormal horizons on magnetic properties, probably corresponding to the tuffs, were observed in the fossil-bearing sedimentary interval. This implies that the massive bio-extinction may link to dramatic environmental changes that were caused by volcanic eruptions.展开更多
This study systematically investigates changes in both compositions and grain-sizes of magnetic minerals in the Chinese loess/paleosol samples (Yichuan, China) during thermal demagnetization processes. Between 100 and...This study systematically investigates changes in both compositions and grain-sizes of magnetic minerals in the Chinese loess/paleosol samples (Yichuan, China) during thermal demagnetization processes. Between 100 and 200℃, (1) Hc and Hcr significantly decrease while Mrs and Ms remain stable; (2) concentration of the multi-domain (MD) grains increases while that of superparamagnetic (SP) grains decreases; and (3) there exists the abnormal behavior of the thermal demagnetization in the natural remanent magnetization (NRM). In addition, the corresponding changes in all these parameters are gradually muted with the increase of the pedogenesis degree. The results indicate that the observed alteration probably relates to reducing processes caused by the burning of the organic matter in samples. Before the thermal treatment, the MD grains in loess samples had been partially altered in nature by low-temperature oxidization (LTD). This CRM can be sufficiently attenuated or even removed by the reducing展开更多
The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials...The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magneto-somes, which are arranged in the form of linear fragmental chain. The distinct differences of magnetic properties between these two samples can be faithfully interpreted in terms of spatial arrangement of magnetosomes and magnetostatic interaction. For the whole cells, the strong intra-chain interactions and weak inter-chain interactions generate behaviors of non-interacting uniaxial single-domain particles. Its δ-ratio is 3.0 and passes the Moskowitz test. In contrast, the isolated magnetosome sample has reduced values of coercivity and δ-ratio (1.5), due to increasing three-dimensional magnetostatic interactions and collapse of magneto-some chains. These observations provide useful insights into applications of the biogenic magnetite (magnetosomes) in magnetic nano-materials and magnetofossils in the paleomagnetic and environmental magnetism.展开更多
Detailed rock magnetic experiments were conducted on high-purity natural crystalline pyrite and its products of thermal treatments in both argon and air atmospheres. In argon atmosphere (reducing environment), the pyr...Detailed rock magnetic experiments were conducted on high-purity natural crystalline pyrite and its products of thermal treatments in both argon and air atmospheres. In argon atmosphere (reducing environment), the pyrite is altered by heating to magnetite and pyrrhotite; the latter is stable in argon atmosphere, and has coercive force and coercivity of remanence of ～20 and ～30 mT, respectively. Whereas in air, the pyrite is ultimately oxidized to hematite. First order reversal curve (FORC) diagram of the end product shows that the remanence coercivity of hematite is up to ～1400 mT. The corresponding thermal transformation process of pyrite in air can be simply summarized as pyrite→ pyrrhotite→magnetite→hematite. These results are helpful for understanding of sedimentary magnetism, secondary chemical remanence and meteorolite magnetic properties.展开更多
In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few pa- rameters using partial anhysteretic remanent magnetization (pAR...In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few pa- rameters 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 rela- tive 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.展开更多
Geomagnetic polarity transitions were the most important phenomena in the study of the geomagnetic field evolution and the earth's deep interior dynamics.The Miocene postcollisional ultrapotassic-potassic rocks ar...Geomagnetic polarity transitions were the most important phenomena in the study of the geomagnetic field evolution and the earth's deep interior dynamics.The Miocene postcollisional ultrapotassic-potassic rocks are widely distributed in the Lhasa Block of southern Tibet.Paleomagnetic studies on the Wuyu Formation indicated that these volcanic rocks recorded the C5Bn.2n-C5Bn.1r and C5ACr-C5ACn geomagnetic polarity transitions.The virtual geomagnetic poles(VGPs) of these two polarity transitions were located in the Atlantic and the central Pacific,respectively.Due to data scarcity,it remains unclear whether VGP paths of Miocene geomagnetic polarity transitions were longitudinal preference and/or 90° away from the sampling sites.展开更多
It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma...It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma) of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval (>500°C) from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E (N=19, A 95=3.9°), and the scatter S B=9.0. The Fisher distribution of virtual geomagnetic poles (VGPs) and the consistence of S B with the expected value at the 95% confidence level indicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path (APWP) curve, suggests no obvious southward movement of the sampling site during the Cretaceous.展开更多
The geomagnetic field may play a key role in orientation and navigation of many long-distance mi- gratory animals. Taking homing and migrating birds as examples, this paper reviews recent progress in studies of geomag...The geomagnetic field may play a key role in orientation and navigation of many long-distance mi- gratory animals. Taking homing and migrating birds as examples, this paper reviews recent progress in studies of geomagnetic "compass" of animals. Moreover, we propose to address two aspects in future geomagnetic orientation research :(1) what are the true components of the "map"? ( 2 ) What are the magneto-receptors and which brain areas acquire and process the geomagnetic field informa- tion ?展开更多
文摘Detailed rock magnetic studies of 55 lavas from Yixian and Fuxin area, West Liaoning, show the primary carriers of remanence to be pseudo-single domain ti-tanomagnetite. K/Ar dating indicates that the volcanic sequence spans 93 to 133 Ma. Stepwise thermal demagnetization successfully isolated well-defined characteristic magnetization (ChRM) in all lavas thermal-treated above 250℃ The mean paleodirections are D/I=5.9°/58.8° (α95 = 2.9°) and D/I =179.2°/-59.9° (α95 = 5.2°) for 27 normally magnetized flows and 28 reversibly magnetized flows, respectively. It indicates that since the Early Cretaceous there is no significant horizontal movement and rotation between the Yixian-Fuxin area and Eurasia. However, Korea Peninsula may have undergone a clockwise rotation of 33.9° relative to the Yixian-Fuxin area during the Cretaceous. On the basis of characteristics of hotspot origins (core-mantle boundary or upper mantle), the clockwise rotation of Korea Peninsula relative to Eurasia is assumed to be
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49425405).
文摘A detailed record of the Matuyama-Brunhes (M-B) transition has been obtained from the loess unit 8 (L8) at Duanjiapo (34.2° N, 109.2° E), Shannxi Province of China. An investigation of the rock magnetic properties using hysteresis loops, thermomagnetic analyses identifies pseudo-single domain magnetite as the main carrier of the rema-nence, with a small contribution from maghemite and hema-tite. The paleo-direction records obtained reveal: ( i ) The M-B transition was recorded in the middle and lower part of L8, and comprises of five fast reversals. (ii) The duration of the M-B polarity transition related to the directional change is about 4800 a. (iii) The virtual geomagnetic pole (VGP) path during the transition is confined over Africa, peaked 90° away from the sampling site, in contrast with the results obtained from the Weinan loess section. The different VGPs are probably attributed to the pedogenesis.
基金the National Natural Science Foundation of China (Grant No. 49834001) and the National Key Basic Research Program (Grant No. G1999075509) and the CAS (Grant No. KZ951-A1-401).
文摘Rock-magnetic and palaeomagnetic studies have been carried out on the interval of famous fossil-bearing sedimentary rocks and its overlying basalts and underlying basalts at the Sihetun section, West Liaoning Province. Normal polarity was obtained for the sedimentary interval and the underlying basalts, while reversed polarity was found in the overlying basalts. Taking account of the new 40Ar/39Ar ages (Swisher et al., 1999), we classified the fossil-bearing sedimentary interval into the Barremian M3n zone (Early Cretaceous age). Several abnormal horizons on magnetic properties, probably corresponding to the tuffs, were observed in the fossil-bearing sedimentary interval. This implies that the massive bio-extinction may link to dramatic environmental changes that were caused by volcanic eruptions.
基金This work was supported by NSF (Grant Nos. EAR 0003421 and EAR/IF 9818704)the National Natural Science Foundation of China (Grant No. 49834001)All the measurements were performed at the Institute for Rock Magnetism, which is funded by the Keck Fo
文摘This study systematically investigates changes in both compositions and grain-sizes of magnetic minerals in the Chinese loess/paleosol samples (Yichuan, China) during thermal demagnetization processes. Between 100 and 200℃, (1) Hc and Hcr significantly decrease while Mrs and Ms remain stable; (2) concentration of the multi-domain (MD) grains increases while that of superparamagnetic (SP) grains decreases; and (3) there exists the abnormal behavior of the thermal demagnetization in the natural remanent magnetization (NRM). In addition, the corresponding changes in all these parameters are gradually muted with the increase of the pedogenesis degree. The results indicate that the observed alteration probably relates to reducing processes caused by the burning of the organic matter in samples. Before the thermal treatment, the MD grains in loess samples had been partially altered in nature by low-temperature oxidization (LTD). This CRM can be sufficiently attenuated or even removed by the reducing
基金supported by the National Natural Science Foundation of China (Grant Nos. 40821091 and 40325011)Hundred Talents Program of the Chi-nese Academy of Sciences and Marie-Curie Fellowship (IIF) Return Phase of (Grant No. MIF1-CT-2005-007555)
文摘The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magneto-somes, which are arranged in the form of linear fragmental chain. The distinct differences of magnetic properties between these two samples can be faithfully interpreted in terms of spatial arrangement of magnetosomes and magnetostatic interaction. For the whole cells, the strong intra-chain interactions and weak inter-chain interactions generate behaviors of non-interacting uniaxial single-domain particles. Its δ-ratio is 3.0 and passes the Moskowitz test. In contrast, the isolated magnetosome sample has reduced values of coercivity and δ-ratio (1.5), due to increasing three-dimensional magnetostatic interactions and collapse of magneto-some chains. These observations provide useful insights into applications of the biogenic magnetite (magnetosomes) in magnetic nano-materials and magnetofossils in the paleomagnetic and environmental magnetism.
基金the National Science Foundation of China (Grant Nos.40221402,40325011,40634024) the Chinese Academy of Sciences Project (Grant No.KZCX3-SW-150)
文摘Detailed rock magnetic experiments were conducted on high-purity natural crystalline pyrite and its products of thermal treatments in both argon and air atmospheres. In argon atmosphere (reducing environment), the pyrite is altered by heating to magnetite and pyrrhotite; the latter is stable in argon atmosphere, and has coercive force and coercivity of remanence of ～20 and ～30 mT, respectively. Whereas in air, the pyrite is ultimately oxidized to hematite. First order reversal curve (FORC) diagram of the end product shows that the remanence coercivity of hematite is up to ～1400 mT. The corresponding thermal transformation process of pyrite in air can be simply summarized as pyrite→ pyrrhotite→magnetite→hematite. These results are helpful for understanding of sedimentary magnetism, secondary chemical remanence and meteorolite magnetic properties.
文摘In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few pa- rameters 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 rela- tive 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.
基金supported by China Geological Survey(Grant No.1212010511704)
文摘Geomagnetic polarity transitions were the most important phenomena in the study of the geomagnetic field evolution and the earth's deep interior dynamics.The Miocene postcollisional ultrapotassic-potassic rocks are widely distributed in the Lhasa Block of southern Tibet.Paleomagnetic studies on the Wuyu Formation indicated that these volcanic rocks recorded the C5Bn.2n-C5Bn.1r and C5ACr-C5ACn geomagnetic polarity transitions.The virtual geomagnetic poles(VGPs) of these two polarity transitions were located in the Atlantic and the central Pacific,respectively.Due to data scarcity,it remains unclear whether VGP paths of Miocene geomagnetic polarity transitions were longitudinal preference and/or 90° away from the sampling sites.
基金supported by National Natural Science Foundation of China (Grant Nos. 40634024 and40821091)
文摘It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma) of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval (>500°C) from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E (N=19, A 95=3.9°), and the scatter S B=9.0. The Fisher distribution of virtual geomagnetic poles (VGPs) and the consistence of S B with the expected value at the 95% confidence level indicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path (APWP) curve, suggests no obvious southward movement of the sampling site during the Cretaceous.
文摘The geomagnetic field may play a key role in orientation and navigation of many long-distance mi- gratory animals. Taking homing and migrating birds as examples, this paper reviews recent progress in studies of geomagnetic "compass" of animals. Moreover, we propose to address two aspects in future geomagnetic orientation research :(1) what are the true components of the "map"? ( 2 ) What are the magneto-receptors and which brain areas acquire and process the geomagnetic field informa- tion ?
