Search

Continuous paleosecular variations reconstructed from sedimentary archives have remarkably deepened our insights into the dynamics of the Earth's magnetic field as well as the chronological purpose. Nevertheless, to construct reliable sedimentary paleomagnetic records in diagenetic reducing sediments is challenging generally due to the pervasive magnetic mineral diagenesis. The relict magnetic minerals are residuals after diagenesis and probably able to record a depositional remanent magnetization, thus it is worthy to explore their paleomagnetic potentials. For this study, two Black Sea sediment cores covering the past 8 ka were subjected to mineralogical and paleo‐ and rock magnetic analyses. Paramagnetic pyrite framboids are pervasive in the studied sediments deposited under anoxic bottom water conditions in the Black Sea. In addition, relict magnetic minerals of ferrous hemoilmenite, Fe‐Mn and Fe‐Cr spinels, and magnetite inclusions are also present in the studied cores. Compared to the previous published paleomagnetic results from the same cores over the last glacial period (20–30 ka) which are dominated by detrital (titano‐)magnetite particles, the studied relict magnetic mineral samples exhibit a similar behavior in recording the depositional remanent magnetization. Furthermore, the obtained paleosecular variations spanning the past 8 ka reproduce the high intensity patterns observed in the regional archeomagnetic and volcanic datasets. Thus, the successful reconstruction of paleomagnetic secular variations from the anoxic Black Sea sediments greatly extend the application of paleomagnetism in sediments deposited in water with a reducing sub‐surface environments from where paleomagnetic data are generally sparse. Plain Language Summary: The Earth's magnetic field can be recorded by magnetic minerals during their deposition within a water column, and are later preserved in sediments. The geomagnetic field signal may be biased if the magnetic minerals are subsequently altered because of changes in bottom water redox conditions. However, relict magnetic minerals are resistant to ambient environmental changes and thus have great potentials to record reliable paleomagnetic signals. To attest this novel idea, we systematically investigated sediments form the Black Sea under strong anoxic bottom water conditions. Our results demonstrate that the relict magnetic minerals survived in the Black Sea sediments covering the past eight thousand years. By comparison with detrital (titano‐)magnetite samples, we found that relict magnetic mineral samples have similar behavior in recording the geomagnetic field. Moreover, the geomagnetic field variations reconstructed from the Black Sea sediments are comparable with other validated regional datasets for the past eight thousand years. Therefore, our new study significantly extends the application of paleomagnetic methods in a wider range of sedimentary redox conditions. Key Points: Relict minerals of hemoilmenite, Fe‐Mn and Fe‐Cr spinels, and magnetic inclusions are magnetic carriers in studied Black Sea sedimentsThe ability in recording the DRM by relict magnetic minerals are comparable with detrital (titano‐)magnetiteThe obtained paleosecular variations resemble reginal field patterns observed in archeomagnetic and volcanic datasets for the past 8 ka [ABSTRACT FROM AUTHOR]

Gyro‐remanent magnetization (GRM) is a frequently occurring yet unwanted remanence contamination for certain samples during alternating field (AF) demagnetization of the natural remanent magnetization. The origin and detailed properties of GRM have not yet been fully understood. In this study, systematic rock magnetic analyses were conducted on marine greigite‐bearing samples of Hole U1433A drilled by the IODP Expedition 349 from the South China Sea. Results show that GRM is mostly acquired above ~55 mT AF demagnetization and can be effectively removed by heating to ~400°C during thermal demagnetization but a secondary tail could remain until ~585°C. In addition, no apparent GRM was observed during the AF demagnetization for the 400°C thermally treated samples. These results strongly suggest that GRM is dominantly carried by single domain (SD) greigite but with minor contributions from SD magnetite. Thus, thermal treatment alone or the hybrid demagnetization (i.e., thermal demagnetization at ~400°C first then systematical AF demagnetization) can efficiently avoid the GRM acquisition and be beneficial for relative paleointensity estimation for greigite‐bearing samples. Besides, GRM carried by greigite has a low thermal stability. Our results also show AF demagnetization spectra of anhysteretic remanent magnetization (ARM) could be strongly distorted by GRM effects due to both have a preference of SD particles. Thus, the median destructive field of ARM is improper to be used as a coercivity proxy for greigite‐bearing samples. Instead, the biplot analysis of AF demagnetization of natural remanent magnetization and ARM can be used to evaluate the relative content of greigite. Key Points: Both greigite and the coexistent magnetite can acquire a GRM during the AF demagnetizationMagnetite lost the ability to acquire a GRM when greigite is disintegrating after first being heated to 400°CGRM can be used as a proxy for semiquantification of greigite concentration [ABSTRACT FROM AUTHOR]

We investigated sea‐surface magnetic anomaly data for the past 5 Myr in the slow‐to‐intermediate spreading South Atlantic Ridge. After error analysis and signal processes, the sea surface magnetic anomaly profiles were downward continued to 1.5 km below sea level, and then the distance from spreading axis was converted to time by matching the observed anomalies with forward models of known polarity reversals. The stacked anomaly profiles from South Atlantic Ridge exhibit short‐wavelength wiggles superimposed on the first‐order variations of magnetic anomalies. The stacked anomaly profiles were first compared with commonly used geomagnetic palaeointensity data synthesized from sedimentary relative intensity records in the past and were further correlated with other available magnetic profiles derived from Central Indian Ridge, East Pacific Rise, and Pacific‐Antarctic Ridge. We found that short wavelength variations in the South Atlantic Ridge can be ascribed to geomagnetic intensity variations from excursions or short polarity events. Spectral analysis of marine magnetic anomalies records reveals that there is no obvious dominant periodicity for the geomagnetic field behavior during the past 5 Myr. Key Points: A long‐term paleointensity record was constructed from sea surface magnetic anomaly data at a slow‐to‐intermediate spreading SAR for the first timeThe newly stacked paleointensity curves agree well with other coeval relative paleointensity dataWe proposed a time scale based on the Earth's paleointensity from marine composite profile for the past 5 Myr [ABSTRACT FROM AUTHOR]

The reversal frequency of the palaeomagnetic field bears great information of evolution of Earth's deep interior. However, there are still debates on the frequency pattern during the older periods of the Phanerozoic. This study investigated the Niutitang Formation (Lower Cambrian) of the Ciye 1 Hole from South China. Rock magnetic results indicate that the dominant magnetic carrier is magnetite. Characteristic remanence magnetizations have been successfully isolated for the weakly magnetized shale rocks through stepwise alternated field demagnetization using the 2G Enterprises Rapid System Magnetometer with a low-noise thin-walled quartz-glass sample holder. Constrained by radiometric ages, our palaeomagnetic results indicated frequent polarity reversals during the period of ∼524–514 Ma, which backs up the speculation about the episode of the Ediacaran–Cambrian (∼550–500 Ma) with a character of reversal hyperactivity. [ABSTRACT FROM AUTHOR]

Early Cenozoic plate collision of India and Eurasia was a significant geological event, which resulted in Tibetan Plateau (TP) uplift and altered regional and global atmospheric circulations. However, the timing of initial collision is debated. It also remains unclear whether the TP was deformed either progressively northward, or synchronously as a whole. As the largest basin in the hinterland of the TP, evolution of the Hoh Xil Basin (HXB) and its structural relationship with development of the Tanggula Thrust System (TTS) have important implications for unraveling the formation mechanism and deformation history of the TP. In this study, we present results from a long sedimentary sequence from the HXB that dates the Fenghuoshan Group to ∼72–51 Ma based on magnetostratigraphy and radiometric ages of a volcanic tuff layer within the group. Three depositional phases reflect different stages of tectonic movement on the TTS, which was initialized at 71.9 Ma prior to the India–Eurasia collision. An abrupt sediment accumulation rate increase from 53.9 Ma is a likely response to tectonic deformation in the plateau hinterland, and indicates that initial India–Eurasia collision occurred at no later than that time. This remote HXB tectonosedimentary response implies that compressional deformation caused by India–Eurasia collision likely propagated to the central TP shortly after the collision, which supports the synchronous deformation model for TP. [ABSTRACT FROM AUTHOR]

A detailed magnetic analysis has been done on sedimentary core of the International Ocean Discovery Program (IODP) Site U1433A during Leg 349 in the South China Sea (SCS). Results show that dominant carriers of the natural remanent magnetization are greigite and (titano) magnetite. The major shift in both declination and inclination at ~ 185 mbsf is assigned to the Matuyama-Brunhes reversal boundary (~ 0.773 Ma). Constrained by biostratigraphic ages, variations in magnetic parameters of the core can be well correlated to the marine oxygen isotope record at glacial/interglacial cycles. Low values of concentration-dependent magnetic parameters correspond to the interglacials, and vice versa. During the interglacial periods, the dominant magnetic minerals are detrital (titano) magnetite and have relatively coarser grain sizes, while fine-grained greigites dominate the glacial periods. This indicates that during the glacials, greigite prevails at the anoxic condition with amount of terrigenous iron oxide caused by the disconnection between the SCS and the Indian Ocean and the exposure of shelf, but digenesis is suppressed at the opposite environment by the high sea level (interglacials). Thus, the preservation/sulfide process of (titano) magnetite is intimately related to the transformation of sea level changes with the monsoon-related rainfall caused by the glacial/interglacial variation. [ABSTRACT FROM AUTHOR]

Continental shelves serve as a bridge between the continent and ocean and sediments in this region are sensitive to land-sea interaction, sea-level variation and local subsidence. In this study, we present a comprehensive magnetic study of the longest sediment core (CSDP-1, 300.1 m) recovered from the South Yellow Sea. The major magnetic minerals in the studied sediments are magnetite, hematite and greigite. Greigite records a chemical remanent magnetization, which can be removed effectively by thermal demagnetization. The magnetostratigraphy defined in this study contains the Matuyama-Brunhes boundary (M/B, 781 ka) at ∼73.68 m, which is consistent with results from adjacent cores. The base of the Quaternary (∼2.6 Ma) in the Yellow Sea is recovered for the first time at a depth of 227.16 m. The basal age of the core is estimated to be ∼3.50 Ma. It indicates that the first transgression of the Yellow Sea occurred no later than ∼1.7 Ma. Succeeding large amplitude regressions occurred in some cold periods such as during MIS 20, MIS 18, and MIS 10. Our results provide the first chronology that brackets the entire Quaternary and we reconstruct the sedimentary evolution of the Yellow Sea with robust age constraints, which provides an important framework for further paleoenvironmental and tectonic studies. [ABSTRACT FROM AUTHOR]

High-resolution paleomagnetic secular variation (PSV) records bear great information of dynamics processes of the Earth’s geomagnetic field, and can be further used for inter-profile correlation and for dating sediments. However, effects of changes in the depositional environment on PSV records have not been fully determined. This study constructed Holocene PSV records for the gravity piston core (ZSQD34) obtained from the northern South China Sea. Rock magnetic and Transmission Electron Microscope (TEM) results indicate that single (SD) and PSD domain magnetites are the main carrier of the natural remanent magnetization. Comparable to the records derived from the freshwater lakes and the modeling results, we observed that direction curves from these two environments of contrasting salinity content are rather consistent. The direction curves are independent of the constructed salinity. However, the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity. Furthermore, on the centennial and millennial time scale, the relative intensity and salinity show some positive relation, suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes. [ABSTRACT FROM AUTHOR]

As one of the longest and most continuously deposited terrestrial sedimentary archives in the world, Chinese loess–paleosol sequences record paleoclimatic and paleomagnetic variations at a range of time scales. Magnetostratigraphic studies provide a first-order chronological framework for Chinese loess sequences. In this review, we highlight recent developments in loess magnetostratigraphy, including pedostratigraphy based on magnetic susceptibility variations. We highlight progress in understanding the mechanisms by which the natural remanent magnetization (NRM) is acquired and discuss in detail the fidelity of paleomagnetic recording in loess records, including the recording of magnetic polarity reversals, excursions, and relative paleointensity variations. Finally, we discuss future prospects for studies of loess NRM. [ABSTRACT FROM AUTHOR]

SUMMARY We report high-resolution palaeomagnetic results across the lower part of S8 in the Luochuan area, northwest of China using parallel subsets samples. A palaeomagnetic anomaly with low palaeointensity and disordered magnetic direction was identified ∼21 ka prior to the Matuyama-Brunhes (MB) polarity reversal, and is consistent with the MB precursor observed from marine sediments and lava flows. This is the first convincing report of the MB precursor in terrestrial material (Chinese loess), which attests the global feature of the MB precursor. Constrained by the stratigraphic position of both the MB polarity reversal and the MB precursor, the loess unit L8 and palaeosol unit S8 of the Chinese loess sequence are undoubtedly tied to the marine isotope stages 18 and 19, respectively. This correlation is critical for an accurate understanding of the correspondences of palaeomagnetic records between the Chinese loess and marine sediments. [ABSTRACT FROM AUTHOR]

SUMMARY A composite Holocene sediment profile ∼5 m in length, constrained by both radiocarbon dating and magnetic susceptibility based correlation, was obtained from three Livingstone piston cores collected in ∼10-m water depth in the Huguangyan (HGY) maar lake, southern China. The homogeneous silty clay indicates stable and continuous deposition. The dominant magnetic carrier is magnetite in the pseudo-single-domain grain size range and thus is suitable for recording palaeomagnetic secular variations (PSV). Results show that the HGY PSV curves can be correlated faithfully to the counterparts at a regional scale. Therefore, the PSV data is a potential tool for stratigraphic correlation and for further refining the chronological framework of lake sediment sequences from Southern China. Further comparison of the HGY PSV records with the coeval European and North American counterparts confirms the existence of strong permanent magnetic flux lobes at the core-mantle boundary. The discrepancy in amplitude and out-phase pattern among the different regional records may be ascribed to the evolution of the magnetic flux lobes. [ABSTRACT FROM AUTHOR]

Abstract: Chinese loess during the Quaternary is important for both paleomagnetic and paleoclimatic studies. Although magnetostratigraphy has been used for the initial loess timescale, paleomagnetic records in loess still remain in debates, such as magnetic polarity anomalies in L9, which is a thick and coarse sandy horizon as a typical marker bed. To better understand the magnetization mechanism of these anomalies, a new age model for L9 was first constructed based on a new correlation between loess and marine δ18O, which proposed that L9 should be correlated to marine oxygen stage (MIS) 20–24, not 22–24 as previous suggested. Using combined grain size and environmental magnetism parameters, an extended climatic optimum corresponding to MIS 21 can be identified in middle of L9. A remagnetization mechanism of viscous remanent magnetization overprinting on characteristic remanent magnetization (ChRM) carriers (mainly large pseudo single domain and multidomain magnetite particles), associated with the chaotic detrital remanent magnetization caused by low efficiency alignment of ChRM carriers along with the ambient field during deposition, is proposed to interpret the magnetic anomalies. This study provides new insights into the magnetization mechanism of the Chinese loess, and the new age model for L9 helps to accurately refine the finer scale correlation of paleoclimatic records between the Chinese loess and marine sediments. [Copyright &y& Elsevier]

Abstract: It is commonly accepted that the climate records in Chinese loess can be correlated well with that in marine sediments. However, discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives. For example, the exact stratigraphic position of the whole Matuyama–Brunhes (MB) transitional polarity zone remains uncertain in Chinese loess. In this study, an accurate transitional zone of the MB reversal from the Mangshan profile, southeast margin of the Chinese Loess Plateau (CLP), was statistically determined using multiple subsets of parallel samples. By integrating results from the central CLP, the whole MB transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between S8 and L8 over a wide region of the CLP. This conclusion further supports that the paleosol unit S8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21, and thus unambiguously supplies an accurate age control in constructing a new loess time scale. [ABSTRACT FROM AUTHOR]

Abstract: New palaeomagnetic and 40Ar/39Ar dating was carried out on the volcanic rocks and interbedded fossil-bearing lake sediments at the Sihetun section (northeast China) to determine the duration of deposition of the lacustrine sediments. The 40Ar/39Ar ages of the lower and upper volcanic rocks near the lava-sediment contacts are respectively 125.7±2.6Ma and 124.2±2.5Ma, which is in good agreement with a previously reported age of tuffs in the lake deposits. This is further supported by a normal palaeomagnetic polarity recorded by the whole lacustrine interval. With these palaeomagnetic investigations and new age controls, we conclude that the whole lacustrine interval at Sihetun was deposited within the normal polarity chron M3n (marine anomaly) during the Early Cretaceous. The possibly volcanic-associated ancient lake may have existed for a relatively short duration of less than 0.7myr, assuming the M3n chron age to be between 124.72–124.04Ma. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: The hominoid fossils found in the Yuanmou Basin, southwestern China, are among the key fossils for understanding the evolution of early hominoids in eastern Asia and their relationship with coeval hominoids in Europe and Africa. However, their exact ages have not yet been well determined. We provide a new high-resolution magnetostratigraphy for the Zhupeng profile, which is one of the fossil-bearing type sections in the region. Based on magnetostratigraphy of 227 remanent directions, together with the age of micromammalian fauna, indicate that the hominoid-bearing layer is dated within polarity chron 3Br 2r or 3Br 1r, i.e. within the interval 7.43–7.38 Ma or 7.34–7.17 Ma. This unambiguously indicates that the Yuanmou hominoid has a late Miocene age, which therefore makes it the youngest hominoid found in Eurasia. It is possible that the Yuanmou Basin provided a refuge for hominoids during a time of major environmental changes. [Copyright &y& Elsevier]

The Chinese loess/paleosol sequences can provide excellent paleomagnetic records for detailed studies on both magnetostratigraphy and secular variations of the Earth’s magnetic field. However, the nature of the loess/paleosol characteristic remanent magnetization (ChRM), isolated by thermal demagnetization from the natural remanent magnetization, still remains in debate. In this study, we directly measure the thermal, alternating field, and low-temperature demagnetization (cooling/warming cycle of remanence in zero field between 300 and 50 K) spectra of ChRM of the loess samples at Touxiangdao, Xining, PR China. The results show that coarse-grained, pseudo-single-domain (PSD)/multi-domain (MD) magnetite and PSD maghemite particles are the main magnetic carriers of the loess and paleosol ChRMs, respectively. By comparing the ChRM characteristics across a loess/paleosol transition zone, we have found that during pedogenesis, the thermally separable ChRM (original detrital remanent magnetization) carried by the PSD/MD magnetite in loess is gradually overprinted by the chemical remanent magnetization carried by PSD maghemite. Even moderate pedogenesis (e.g., for the pedogenically altered loess) can strongly affect the loess ChRM. Thus more attention has to be focused on the paleosol ChRM separated solely by thermal demagnetization, especially when constructing a continuous paleomagnetic record covering both loess and paleosol units. [Copyright &y& Elsevier]

• A refined magnetostratigraphy for the last 6.5 Ma is reconstructed. • A greigite-bearing layer occurs at 2.53-2.55 Ma. • Magnetic parameters record the East Asian monsoon evolution since 6.5 Ma. The South China Sea (SCS) has become a global focus for paleoclimatic and paleoceanographic studies due to its location, which makes it highly sensitive to the East Asian monsoon and to Pacific Ocean changes. We present here a refined magnetostratigraphy for the last 6.5 Ma for Hole U1431D, which was recovered during IODP Expedition 349 in the central SCS. Magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite-bearing layer at 130.5-132.0 meters below sea floor. The greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event. Environmental magnetic results indicate that the East Asian summer and winter monsoon were stable from 6.5 to 5 Ma. The summer monsoon intensified at 5 Ma, and then weakened gradually since 3.8 Ma. In contrast, the winter monsoon weakened at 5 Ma, and has then been enhanced since 3.8 Ma and more stable from 0.6 Ma. Spectral analysis indicates that the East Asian summer monsoon was driven directly by low-latitude insolation changes before ∼3.2 Ma, and that it has been affected by both low-latitude insolation and high-latitude ice volume changes since ∼3.2 Ma. [ABSTRACT FROM AUTHOR]

Abstract: Sediments from the continental shelf/coastal region bear significant signals of sea-level, climate change as well as local tectonic information. This study presents a high-resolution magnetostratigraphic and rock magnetic study of a 212.4m core (BH08, with a basal age of 1.06Ma) recovered from the shallow (<30m below sea level) Bohai Sea, China. Astronomical tuning based on the sediment redness (a*) of core BH08 allows the construction of a high-resolution chronology that is assisted by magnetostratigraphic data. Sedimentology and associated proxies (grain size and redness) indicate that the cyclic alternation of neritic/littoral sandy deposits and terrestrial silts/clayey silts was mainly controlled by changes in sea-level and associated base-level at glacial–interglacial timescales. The a* record of the core can be correlated with marine δ18O records at 40- and 100-kyr cycles, indicating that the sediments in the study area are continuous at least at orbital timescales regardless of significant base-level variations. This is likely due to continued subsidence in the basin and creation of accommodation space. The significant lower sedimentary accumulation rates since 750ka might be due to the deviation of the depositional locus from core site because of extreme low sea-level stands during the glacials since the Mid-Pleistocene transition (MPT). Especially the glacial sea-level lowstands might have resulted in bypassing or erosion of sediments on the BH08 core site during peak glacials (MIS 6, MIS 10 and MIS 16), limiting the sediment preservation potential. This study documents the longest Quaternary sedimentary succession in the Bohai Sea and provides, for the first time, a clear link between sedimentation in the area and glacial–interglacial climate-driven sea-level changes. This study also highlights the feasibility of astronomical tuning to obtain high-resolution chronology for shallow shelf deposits, which is otherwise very difficult to be achieved on the basis of magnetostratigraphic data alone. [Copyright &y& Elsevier]

Abstract: A combined palaeomagnetic and geochronologic study has been conducted on a basaltic lava sequence of five flows at Jianchang in Liaoning Province, northeastern China. Radiometric 40Ar/39Ar dating indicates that the volcanism occurred at about 119Ma within the marine anomaly C34n in Cretaceous normal superchron (CNS). Rock magnetic investigations show that pseudo-single domain (PSD) or a mixture of single domain and multi-domain grain titanium-poor titanomagnetite is dominant in the studied lava flows. Both stepwise thermal and alternating field demagnetizations isolate the well-defined normal characteristic remanent magnetization (ChRM) in five independent lava flows with a mean direction of D/I =11.1°/57.2° (α 95 =5.7°). Palaeointensity was determined using the Coe modified Thellier method with systematic partial thermoremanent magnetization (pTRM) checks. All together, 61 samples from 286 samples with positive pTRM and tail checks yield palaeointensities ranging between 10.1 and 73.6μT. To further check the effects of thermal alteration on the palaeointensity results, a new ratio (M rs,480°C/M rs,25°C, where M rs,25°C and M rs,480°C are the room temperature saturation isothermal remanent magnetizations for the raw sample and the product after a 480°C thermal treatment, respectively) is proposed. Results show that the ratio changes significantly even for those samples with positive pTRM check. We further put forward that palaeointensity results are acceptable with ratio between 0.9 and 1.1. With this new criteria, 17 samples show consistent palaeointensity results with an average of 20.0±3.2μT. This value corresponds to the virtual dipole magnetic moments (VDM) of (3.5±0.6)×1022 Am2, which is about half of the value of present field. This finding, combined with other available results, suggests that magnetic field of the Earth just at the onset of the CNS is characterized by a weak palaeointensity. [Copyright &y& Elsevier]

The Hawaiian-Emperor volcanic chain (H-E chain) is located in the middle of the North Pacific Ocean. It extends from northwest to southeast, including two segments, the older Emperor chain and the younger Hawaiian chain between which is a 60o change in strike, here termed the H-E bend. The H-E chain is the clearest and most intensively researched hot spot track in terms of plate motion, mantle plumes, tectonics, geochemical evolution, and lithospheric studies. However, debates on the formation of the H-E chain, in particular the H-E bend, concerning its origin in hot spot drift and/or Pacific plate motion change, have been ongoing for several decades. In this paper, we review current understanding and ideas concerning this debate and suggest ways forward. So far, neither hot spot southerly drift nor Pacific plate motion change can perfectly account for the geometry and progression of the H-E chain. In this review, we put forward a joint model where these two competing processes together can reasonably explain the evolution of the H-E chain and the H-E bend. In addition, we proposed three stages for formation of the H-E chain, including: 1) A ridge-plume interaction stage: Meiji~Detroit seamounts and a possible subducted section; 2) A combination of hot spot-Pacific plate motion: South of Detroit seamount ~ H-E bend; and 3) Pacific plate motion with a fixed hot spot: Hawaiian volcanic chain. In addition, any plate movement at the surface must be balanced by motion deeper in the mantle. Therefore, we consider that the surface Pacific plate motion and the state of deep mantle plume at 47–55 Ma are not totally separated but co-evolved. Furthermore, reconstructions of the Pacific plate and its boundaries should be considered if Hawaiian hot spot motion makes great contributions to the formation of the H-E chain. Nevertheless, establishing the causal links between these events and their underlying dynamic triggers requires further, more comprehensive work. [ABSTRACT FROM AUTHOR]

Do non-dipole geomagnetic field behaviors persistently exist in the subarctic Pacific Ocean over the past 140 ka? Paleomagnetic records from globally distributed locations are essential for fully understanding geomagnetic field variations, particularly non-dipole field fluctuations [1]. The weak field intensities during ~64-70 and ~15-17 ka indicate decay of the dipole field and probably growing dominance of non-dipole fields [13]. Dipole field dominance, extremely high- and low- latitude flux patches, and weak Pacific hemisphere variations are robust field characteristics that have occurred over the past few hundred years [15]. [Extracted from the article]

Magnetic properties of rocks are crucial for paleo-, rock-, environmental-magnetism, and magnetic material sciences. Conventional rock magnetometers deal with bulk properties of samples, whereas scanning microscope can map the distribution of remanent magnetization. In this study, a new scanning microscope based on a low-temperature DC superconducting quantum interference device (SQUID) equipped with an in-situ magnetization/demagnetization device was developed. To realize the combination of sensitive instrument as SQUID with high magnetizing/demagnetizing fields, the pick-up coil, the magnetization/demagnetization coils and the measurement mode of the system were optimized. The new microscope has a field sensitivity of 250 pT/√Hz at a coil-to-sample spacing of ∼350 µm, and high magnetization (0–1 T)/ demagnetization (0–300 mT, 400 Hz) functions. With this microscope, isothermal remanent magnetization (IRM) acquisition and the according alternating field (AF) demagnetization curves can be obtained for each point without transferring samples between different procedures, which could result in position deviation, waste of time, and other interferences. The newly-designed SQUID microscope, thus, can be used to investigate the rock magnetic properties of samples at a micro-area scale, and has a great potential to be an efficient tool in paleomagnetism, rock magnetism, and magnetic material studies. [ABSTRACT FROM AUTHOR]

Paleomagnetic secular variation (PSV) provides information on the mechanisms of the geodynamo and can also be used for stratigraphic correlation on a regional scale. In this study, we constructed PSV curves of relative rapidly deposited Holocene marine sequence from East China Sea. Results show that the dominant magnetic carriers are pseudo-single domain (PSD) to multidomain (MD) magnetites. Paleomagnetic directions are preserved by coarse-grained magnetite, even affected by post-depositional diagenetic alteration. The PSV record of core MD06-3040 exhibits six major inclination peaks and five declination swings during the Holocene. The periodicities for inclination are about 2000 and 550 years, and for declination are about 1400 and 500 years. The PSV of MD06-3040 is comparable to archeomagnetic and historic results for the last 2500 years and to PSV results from lake sediments in southern China and Japan during the Holocene. A PSV stack of East Asia is constructed by sedimentary and archeological PSV results, which can be used as an important reference curve for a large region, and the PSV correlation between sites can be applied for relative dating of East Asia. [ABSTRACT FROM AUTHOR]

Abstract: Magnetostratigraphic studies have established a first-order chronological framework for the Paleolithic sites in the Nihewan Basin (North China), which enabled tracking early human evolution in East Asia. However, to fully understand how well early humans were adapted to climate change, a truly precise dating of the Paleolithic sites is required. Here, we established a high-resolution astronomical timescale for the Xiantai and Donggutuo fluvio-lacustrine successions at the eastern margin of the Nihewan Basin employing low-field magnetic susceptibility (χ) as a climatic indicator, aiming to further refine the ages of the Xiantai, Donggutuo and Maliang Paleolithic sites. Starting from an initial age model constrained by geomagnetic reversals, larger-scale χ cycles were firstly tuned to orbital obliquity using an automatic orbital tuning method. This first-order tuning was followed by simultaneously tuning χ to both obliquity and precession. The finally tuned χ records can be correlated almost cycle-by-cycle with the quartz grain-size record of the Chinese loess sequence and the marine δ 18O record. The astronomically estimated age of the Xiantai Paleolithic site is ca. 1.48Ma, corresponding to paleosol layer S20 of the Chinese loess sequences or marine oxygen isotope stage (MIS) 49, an interglacial period. The astronomical estimate for the Donggutuo Paleolithic site ranges from ~1.06Ma to 1.12Ma, corresponding to paleosol/loess layers S11–S12 or MIS 31–33, spanning both interglacial and glacial periods. The astronomically estimated age of the Maliang Paleolithic site is ~0.79Ma, corresponding to loess layer L8 or MIS 20, a glacial period. This astronomical finding further implies that early humans may have permanently occupied China as far north as 40oN since at least 1.1Ma, and before this time the occupation may be intermittent. [ABSTRACT FROM AUTHOR]