Petro-and paleomagnetic investigations of Tuzla section sediments (krasnodarsk territory)

Petro-and paleomagnetic methods are applied to the study of the upper part of the Late Pleistocene Tuzla section (Azov coast of the Taman Peninsula) composed of continental sediments and dated at 50–10 ka. The detailed curves of the angular components of the geomagnetic field obtained in this study display an anomalous direction coinciding in time (～25–35 ka) with an anomalous horizon discovered in rocks of the Roxolany section (Ukraine). According to the world time scale of geomagnetic excursions, the anomalous direction correlates with the Mono Lake excursion. A significant correlation between the time series NRM_0.015/SIRM (Tuzla section) and NRM₂₅₀/KB (Roxolany section) in the interval 50–10 ka and the world composite curves VADM-21 and Sint-800 implies that, in this time interval, the curve NRM_0.015/SIRM reflects the variation in the relative paleointensity of the geomagnetic field.     

Wavelet analysis of paleomagnetic data: 5. Early Jaramillo reversal and main characteristic times in the interval from 3 to 70 ka in the variations of the elements of geomagnetic field (Western Turkmenia)

The data on the variations in the elements of the geomagnetic field with the characteristic times of 3–70 ka during the 180-ka interval that includes the final stage of the Matuyama chron, the Jaramillo subchron, and the Early Jaramillo reversal are presented. A series of particular features are revealed in the variations. It is shown that such detailed characteristics of the variations, which might be critical for identifying the causes of the reversals, can only be derived by thorough investigation of the sedimentary rocks that were accumulated during very long time intervals (many hundreds of years) and slowly cooling intrusions.     

Geomagnetic Field Intensity during the Neolith in the Central East European Plain

The conducted archeomagnetic studies resulted in data on variations in the geomagnetic field intensity in the central East European Plain (Sakhtysh I site area, ? = 56°48′ N, λ = 40°33′ E) during the time interval of 5–3 ka BC. The geomagnetic field intensity varied mainly within the range of 30–60 μT. In the first half of the 5th millennium BC, the mean level of geomagnetic field intensity was about 35 μT. In the second half of the 5th–early 4th millennium BC, it rose to about 50 μT and then decreased again to reach a mean value of about 40 μT in the period of 4–3 ka BC. Comparison of the geomagnetic field intensity variation based on the obtained data and the data on the Caucasus region for the same time interval demonstrates a certain similarity.     

The geomagnetic field recorded in sediments of the Tuzla section (the Krasnodar Territory,Russia) over the time interval 120–70 ka

Petro-and paleomagnetic methods are applied to the study of the lower part of the Early Pleistocene Tuzla section on the Black Sea coast of the Taman Peninsula, This part of the section is composed of marine and lagoonal sediments deposited over the time interval 120–70 ka. The measured curves of the variation in the geomagnetic field inclination reveal an anomalous direction dated at ～110 ka that coincides with a similar anomalous direction in the Eltigen section (Ukraine) correlating with the Blake paleomagnetic event. The significant correlation between the time series NRM_0.015/SIRM_0.015 (Tuzla section) and the world composite Sint-800 curve indicates that the curve NRM_0.015/SIRM_0.015 in the interval 110–70 ka actually reflects the variation in the relative paleointensity of the geomagnetic field.     

Variations of the main geomagnetic field intensity in the region of the Taman Peninsula during the last 13 centuries

The archaeomagnetic studies of ceramics from the Hermonassa multilayer archaeological monument in the Taman Peninsula provided the data on the intensity of the main geomagnetic field in the past. The data for the interval from VIII to XX centuries A.D. demonstrate a well pronounced decreasing trend in the geomagnetic field intensity during this time. Three stages, each lasting for a few centuries, are distinguished in the variations of the centennial average field which slightly varies within each stage and generally decreases from 70 to ~45 μT during the entire period from VIII to XX centuries A.D. The variations of the geomagnetic field in the interval from XII to XVII centuries A.D. have a form of quasi-harmonic oscillations with a characteristic time of about 300 years.     

An estimate of late Pleistocene geomagnetic intensity variation from Sulu Sea sediments

Sediments from Site 769 of the Ocean Drilling Program's Leg 124 provide a record of geomagnetic intensity variation over the past 110 ky. Using continous shipboard measurements exclusively, I estimate the variation in the geomagnetic field strength by employing low-field magnetic susceptibility as a normalization parameter for the measured remanence intensity. By calibrating the resultant relative paleointensity record against previously available Holocene age estimates of absolute paleointensity, I derive an estimate of virtual dipole moment since 110 ka. The record obtained from these Sulu Sea sediments is strikingly like that previously obtained from sediments of a similar age in the Mediterranean Basin with distinct intervals of low intensity near 15, 20, 40 and 65–70 ka. The Sulu sediments also indicate a low-intensity feature near 108 ka. Important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non-dipolar component of the geomagnetic field might have been present at that time.     

Geomagnetic field intensity in the eastern Mediterranean region in the second half of the 1st millennium BC and the beginning of our era

The magnetization of ceramic material manufactured in the eastern Mediterranean is studied. Data on the variation in geomagnetic field intensity in the time interval from the fourth-quarter of the 6th century BC through the 2nd century AD are obtained. The main tendency of the variation in the field intensity until approximately the middle of this interval is its decrease, after which the average intensity level varied insignificantly over the three next centuries. Variations with characteristic times of a few tens to a few hundreds of years are superimposed on the smooth variation in the field intensity approximated by a sinusoid with a period of 1600 yr. The data obtained in this work confirm the previously derived conclusion that short-term intensity variations have been permanently present in the geomagnetic field in the recent millennia.     

Geomagnetic field variations as determined from bulgarian archaeomagnetic data

The archaeomagnetic determinations obtained from the collections of archaeological materials, dated in the last 2000 years are summarized. The review describes the materials used, the methodology applied, the local database organization, the principles of data processing and smoothing procedures. Errors evaluation at different levels of analysis of the experimental results are described. Special attention is paid to the archaeointensity determinations. Some rock magnetic properties studied in connection with the difficulties in the Thellier method are summarised. The curves of geomagnetic field elements variations for the last 2000 years for Bulgaria are shown. The Bauer plots, VGP path and VDM curve are also discussed, the latter confirming the general decrease in the strength of the geomagnetic field from the beginning of this era to the present. Westward drift of the geomagnetic field non-dipole part cannot be considered proved yet for the time interval 7th to 13th Centuries AD from the Bulgarian directional data.     

The results of wavelet-analysis of series of archaeomagnetic data on the geomagnetic field intensity

We analyze the results of wavelet analysis of series of archaeomagnetic data on the geomagnetic field’s intensity over the past 7500 yrs performed by Gurarii and Aleksyutin and presented in the paper “Wavelet Analysis of Basic Archaeomagnetic Series of Data on Geomagnetic Field Intensity over the Past 7500 Years” [Gurarii and Aleksytin, 2009]. The results in themselves are beyond question, but their interpretation given in the aforementioned paper is very controversial. Analyzing these results, we arrive at the conclusion that the periods of variations identified reliably (very strongly or identified in a long time interval) lie within certain bands with about 300-, 500-, 750-, and 1600-yr centerlines. The conclusion is drawn on the existence of general regularities in the behavior of geomagnetic field variations.     

Paleomagnetic record in the Late Pleistocene loess-soil deposits of the Pekla section in the time interval 425–50 Ka

The composition, granulometry data, and concentration of grains that carry the natural remanent magnetization (NRM) are studied in the bottom 6.5 meters of the loess-soil deposits of the Pekla section (Azov coast, Krasnodar region). It was shown that these strata, which correspond to the 9th–11th marine oxygen isotope stages (MIS) and cover the time interval ∼425–300 ka, are suitable for further paleomagnetic investigation. The deposits in the upper portion of the Inzhavino paleosoils (Likhvin Interstadial) contain the records of anomalous deviations of the direction of magnetization from the dipole field at the sampling site. The studied interval was sampled by taking two hand blocks from four sampling levels, which minimizes the errors due to the specimen cutting. This anomaly dated ∼300 ka possibly corresponds to the Biva-II geomagnetic excursion. However, the studies of implications of anisotropy in magnetic susceptibility (AMS) for the direction of natural remanent magnetization (NMR) have shown that parts of the samples from the Inzhavino paleosoils and the underlying loess horizon are magnetically anisotropic, which is characteristic for biogenic magnetite grains, while other parts of the samples exhibit plane anisotropy typical for natural sedimentary structures. A weak correlation between the time series of averaged curves of relative paleointensity, NRM₂₀/ARM₂₀ (and NRM₂₀/K) for the loess horizons of the Pekla section and the global composite reference curve of relative paleointensity, Sint-800, in the time intervals 200–130 ka and 370–320 ka indicates that the paleomagnetic records have been imprinted not only on the detritic magnetic grains but also on the grains produced by chemical reactions and the life processes of bacteria.     

Archaeomagnetic study of ceramics from the El Molon archaeological monument (Spain

Data on the geomagnetic field intensity in the first millennium BC and the 8th–10th centuries AD are obtained from the study of materials from the El Molon archaeological monument (Spain). A 75-yr averaged curve of the variation in the geomagnetic field intensity in the area of the zero meridian over the last three millennia is constructed from a set of new and previously obtained data on the geomagnetic intensity variations in Spain and France. The field intensity smoothly decreases in the time interval studied, and variations a few centuries long are superimposed on this trend. Unlike the present-day relationship, the average level of the geomagnetic field intensity in Spain in the first millennium BC was higher than in the Caucasus.     

Variations of angular elements of the geomagnetic field in Europe during the last 24 centuries

The analysis of variations in angular elements of the geomagnetic field during the period since 350 B.C. to the present day according to the findings from the study of thermal magnetization of baked archaeological samples from England, France, and East Europe showed that the key feature in the behavior of the geomagnetic inclination in all three regions is a millennial variation. The trend in the behavior of the inclination of the geomagnetic field can be regarded as a manifestation of a variation with a characteristic time scale of several thousand years. Despite the general likeness of variations in inclination and declination of the ancient geomagnetic field, they also exhibit a noticeable dissimilarity. The paths of the virtual geomagnetic pole reconstructed from the variations of angular elements of the geomagnetic field in East Europe indicate that the geomagnetic polar motion is quasi-cyclic. The duration of the first cycle was about 1000 years, while the second cycle has not been completed due to the change of the motion to the opposite direction in the middle of the XVII century.     

Archaeomagnetic study of ceramics from the Neolithic Los Castillejos multilayer monument (Montefrio,Spain)

The geomagnetic intensity variation from the middle of the 4th millennium BC to the beginning of the 2nd millennium BC is reconstructed from the archaeomagnetic study of ceramic material taken from 24 layers of the Los Castillejos monument (Montefrio, Spain). The general patterns of the geomagnetic intensity variation reconstructed by studying materials from the Cendres Cave and Los Castillejos monuments (Spain) are similar. The intensity level is revised in the time interval including the minimum of the “fundamental” oscillation of the geomagnetic field; the characteristics of geomagnetic intensity variations whose superposition can provide the intensity variation observed in the study time interval are determined. Constraints on the climate humidity variation over the settlement lifetime are obtained from heating-induced variations in the magnetic susceptibility of the ceramics.     

Global anomalies of the main geomagnetic field and the dynamic model of their sources

The model of the main geomagnetic field sources, including 12 more dipoles in addition to the main dipole, is presented. The source parameters have been determined for the 100-year-long period at an interval of 5 years. The problem is solved using the iteration method proposed and developed by the authors. Six more sources have been included in the iteration process at its current step. This made it possible to substantially smooth the time variations in the dipole parameters obtained previously and, on the other hand, to describe all global anomalies of the main geomagnetic field using this model. A change in the parameter values can be approximated by rather smooth functions describing specific features of development of the sources operating for 20–30 years. However, the short duration of the obtained series (21 points) makes the problem of prediction substantially more difficult. The parameters of 13 dipoles, extrapolated for 2000 using the linear prediction filter, are in good agreement only with the general development of the sources.     

Manifestation of the Gothenburg geomagnetic field excursion in the Barents Sea bottom sediments

An analysis of the paleomagnetic characteristics of the bottom sediments taken in 2000 in the northern Barents Sea for the first time revealed the Gothenburg geomagnetic field excursion (13 000–12 000 years ago) at the time boundary of the transition from the glacial period to the recent warm epoch (the Holocene). The obtained data confirm the excursion complex structure: the presence of two successive time intervals of variations in the geomagnetic field inclination. An increase in the magnetic susceptibility and natural remanent magnetization of the samples at the above boundary and about 15 000 years ago indicates that the magnetic parameters of the sediments respond to climate changes in the environment in this time interval.     

Wavelet analysis of paleomagnetic data: 4. Characteristic short times (0.4–4.5 ky) of variations in the elements of the geomagnetic field during the early Jaramillo reversal and in the stationary field during the Matuyama and Jaramillo chrons (Western Turkmenia)

The geomagnetic variations with characteristic times ranging from 0.4 to 15 ka are shown to be largely stochastic. Variations with different characteristic times appear during different time intervals and reflect accelerating and decelerating processes. The variations do not exhibit any predominant times. At the same time, almost periodic variations in the lithological characteristics are clearly seen in the wavelet diagrams of the parameters that reflect the changes in the composition (quantitative and qualitative) of ferrimagnetic material; i.e., the changes in the conditions of sedimentation related to climate variations. The variations with periods of 5, 8.5, and 13 ka are concurrent with the similar variations in the paleomagnetic data, while the variations with a period of 3.5 ka are only observed in the magnetic parameters. We suggest that the first mentioned oscillations reflect the changes of the external (relative to the Earth) origin, whereas the changes with a period of 3.5 ka are caused by some terrestrial factors.     

基于地磁场相对古强度变化的下蜀黄土年代序列及其古气候意义

分布于宁镇地区的下蜀黄土年代标尺研究薄弱.我们以镇江大港钻孔岩芯的下蜀黄土为例,探讨了下蜀黄土记录地磁场相对古强度的可靠性.岩石磁学的实验显示,下蜀黄土大体上符合估计相对古强度对沉积物的要求.以低频磁化率()作为天然剩磁(NRM300)的归一化因子,我们获得了下蜀黄土记录的地磁场相对古强度变化.通过与邻区和全球的单个及合成曲线的对比,我们发现大港钻孔岩芯的相对古强度记录展现出主要的全球偶极场的变化特征,因而可用于建立下蜀黄土的年代标尺.新的年代标尺表明,大港钻孔的磁化率年代序列与北方黄土无法直接对比,证实了该地点的下蜀黄土磁化率变化机制与北方的不同.大港钻孔下蜀黄土的沉积速率与磁化率相关,低风尘沉积速率对应低磁化率,是降水增加所导致的结果.沉积速率与磁化率年代序列显示,下蜀黄土记录的本区季风变化过程可分为4个阶段.阶段Ⅳ(819～700ka)对应中更新世转型阶段,东亚季风降水较少.阶段Ⅲ(700～412ka)对应中更新世的大间冰期,东亚季风降水最多.阶段Ⅱ(412～197ka)时东亚季风降水减少,较阶段Ⅳ略少.阶段Ⅰ(197～34ka)东亚季风降水最少.因此,中更新世气候转型后,长时间尺度东亚季风降水持续减少,可能受全球温度阶段性降低驱动.     

Solar cyclic variation in magnetic elements of Moscow observatory

The data of Moscow observatory for the 1946-2006 interval of observations are analyzed in order to detect long-term geomagnetic variations related to solar activity against a background of the secular variations in the geomagnetic field.     

The geomagnetic field at the Paleozoic/Mesozoic and Mesozoic/Cenozoic boundaries and lower mantle plumes

The data on the amplitude of variations in the direction and paleointensity of the geomagnetic field and the frequency of reversals throughout the last 50 Myr near the Paleozoic/Mesozoic and Mesozoic/Cenozoic boundaries, characterized by peaks of magmatic activity of Siberian and Deccan traps, and data on the amplitude of variations in the geomagnetic field direction relative to contemporary world magnetic anomalies are generalized. The boundaries of geological eras are not fixed in recorded paleointensity, polarity, reversal frequency, and variations in the geomagnetic field direction. Against the background of the “normal” field, nearly the same tendency of an increase in the amplitude of field direction variations is observed toward epicenters of contemporary lower mantle plumes; Greenland, Deccan, and Siberian superplumes; and world magnetic anomalies. This suggests a common origin of lower mantle plumes of various formation times, world magnetic anomalies, and the rise in the amplitude of geomagnetic field variations; i.e., all these phenomena are due to a local excitation in the upper part of the liquid core. Large plumes arise in intervals of the most significant changes in the paleointensity (drops or rises), while no correlation exists between the plume generation and the reversal frequency: times of plume formation correlate with the very diverse patterns of the frequency of reversals, from their total absence to maximum frequencies, implying that world magnetic anomalies, variations in the magnetic field direction and paleointensity, and plumes, on the one hand, and field reversals, on the other, have different sources. The time interval between magmatic activity of a plume at the Earth’s surface and its origination at the core-mantle boundary (the time of the plume rise toward the surface) amounts to 20–50 Myr in all cases considered. Different rise times are apparently associated with different paths of the plume rise, “delays” in the plume upward movement, and so on. The spread in “delay” times of each plume can be attributed to uncertainties in age determinations of paleomagnetic study objects and/or the natural remanent magnetization, but it is more probable that this is a result of the formation of a series of plumes (superplumes) in approximately the same region at the core-mantle boundary in the aforementioned time interval. Such an interpretation is supported by the existence of compact clusters of higher field direction amplitudes between 300 and 200 Ma that are possible regions of formation of world magnetic anomalies and plumes.     

Variations in the geomagnetic field strength in the 5th–3rd centuries BC in the eastern Mediterranean (according to narrowly dated ceramics)

The magnetization of ceramics from the eastern Mediterranean dated within a short period (mostly shorter than ±20 years) has been studied, which made it possible to specify the geomagnetic field variations on the time interval 5th–3rd centuries BC. The 11-year time series of the geomagnetic field strength values has been constructed. The field strength changes have been considered, which indicated that the centennial variation with a characteristic time of ～130 years (according to the obtained data) is observed on this time interval as well as during the last two millennia. The ceramic material from the Mayskaya Gora archeological site (Taman), the preparation succession of which was established based on the shape of pottery but the problem of absolute dating was not solved, has been dated.