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1.
Emanuela De Marco Evdokia Tema Philippe Lanos Despina Kondopoulou 《Studia Geophysica et Geodaetica》2014,58(1):121-147
We present an updated compilation of Greek directional archaeomagnetic data for the last 4.5 millennia. The data set comprises 89 directions from archaeological artefacts and volcanic rocks. Most of the data come from the Late Bronze Age (1700-1400 BC) that is the flourishing period of the Minoan civilization in Crete, while parts of the classical (480-323 BC), Hellenistic (323-31 BC) and Roman (146 BC-330 AD) periods are also well covered. The dataset has been analysed using the Bayesian approach for curve building and a directional secular variation (SV) curve for Greece is proposed. Comparisons with regional and global model predictions show a general agreement even though some discrepancies are observed for some time intervals. The new curves together with the previously published intensity SV curve for Greece, also using the Bayesian approach, form a homogeneous set and enrich our knowledge of the full geomagnetic field vector variation in Greece during the last millennia. 相似文献
2.
Revealing the evolution of the past geomagnetic field is of dual interest. It is crucial to estimate the conditions of the Earth's deep interiors, while it offers a reliable absolute dating tool of burned archaeological artifacts. Although a substantial effort was paid during the last decade to construct a reference archaeomagnetic curve for Mesoamerica, mostly absolute intensity variations are revealed for the previous three millennia. Here, we report an updated directional (inclination and declination) reference secular variation curve based on volcanic lava flows and archaeological artifacts carrying full thermoremanent magnetization. A bootstrap method with penalized cubic b-splines was used to develop the directional curve. Relocation error exercise and strict selection criteria allowed to use 82 well-defined palaeodirections. Both data distribution density and the firm relationship between the ages and samples, ensure the reliability of the curve for the dating purposes. The combination of directional data with available intensity variation highlights some sudden geomagnetic field fluctuations. 相似文献
3.
A palaeomagnetic record of geomagnetic secular variation during the last 7000 years has been obtained from the sediments of Loch Lomond, Scotland. The magnetic direction fluctuations repeat well between cores and show greater detail, especially over the last 5000 years, than other European records. A time scale has been derived from14C analyses on the Lomond sediment and comparison with other14C-dated sediments. Investigation of relative palaeointensity determination methods has shown that the widely used normalization parameter of partial ARM is insensitive to even small sediment grain size fluctuations.The new high-fidelity direction record and improved time scale show that geomagnetic field changes have not followed a simple oscillatory pattern during the last 7000 years. The record enhances the application of palaeomagnetism to dating recent sediments, as the main declination swings are now characterized by fine detail, and paired inclination data are also available. The problem of mismatching swings when correlating with other paired directional records is thus reduced.The palaeomagnetic record agrees well with some archaeomagnetic results. It confirms the period of anticlockwise motion of the geomagnetic field vector, between 1000 and 600 years B.P., which was first documented by English archaeomagnetic investigations. Clockwise motion is shown to predominate during the remainder of the last 5500 years. The VGP path does not correlate with that of Japanese archaeomagnetic results nor North American sediment data from 2000 to 0 years B.P. This suggests that the secular changes are dominated by local non-dipole sources rather than wobbling of the main geomagnetic dipole. 相似文献
4.
Fco. Javier Pavón–Carrasco Maria Luisa Osete J. Miquel Torta Luis R. Gaya–Piqué 《Pure and Applied Geophysics》2008,165(6):1209-1225
The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco
et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian
European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the
palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development
showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken
of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model
for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an
improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to
study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The
pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented
by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters,
opening the door for more discussions on this challenging subject. 相似文献
5.
R. Thompson 《Physics of the Earth and Planetary Interiors》1984,36(1):61-77
Spherical harmonic coefficients of the geomagnetic field, calculated from historical observations of declination, inclination and intensity, and from archaeomagnetic inclination results, have been used to produce a film of geomagnetic change since 1600 A.D. The non-dipole geomagnetic field is found to be constantly changing: no fixed or standing non-dipole features are observed. Non-dipole foci are seen to have lifetimes of a few hundred years. The westward drift, which was an important feature of the 18th and early 19th century geomagnetic field, was less pronounced in the 17th century. The growth, evolution, decay and replacement of non-dipole foci, but not their movement are found to have been the major features producing century-long secular directional magnetic variation. Most of the low degree and order spherical harmonic coefficients have changed significantly over the last few hundred years. In particular the change in sign of the axisymmetric quadrupole around 1837 A.D. is noted. Sustained, century-long, intensity changes, however, appear to have been dominated by variations in the intensity of the centred dipole, rather than by non-dipole field fluctuations. 相似文献
6.
Abstract A single layer of widespread tephra deposits possibly can provide an instantaneous record of the past geomagnetic field and potentially can indicate even a small-scale tectonic rotation compared to a range of geomagnetic secular variations. We report paleomagnetic data of the Ebisutoge–Fukuda tephra, which is dated at approximately 1.8 Ma and is distributed in central Japan between the Osaka–Kyoto area and the Boso Peninsula. The Fukuda volcanic ash layer and its correlative ash deposits in the Osaka–Kyoto area, near Lake Biwa and in the Mie and Niigata areas yield identical site mean declinations of approximately −170° after tilt correction, whereas moderate inclination shallowing is observed in the upper unit at several localities. Anisotropy measurements both of low-field magnetic susceptibility and of anhysteretic remanent magnetization suggest that the inclination shallowing results from the biased alignment of magnetic grains, which were deposited in the fluvial environment. The source volcanic unit, Ebisutoge pyroclastic deposits in the Takayama area, yields a mean declination of approximately −155°, showing clockwise deflection from the magnetic directions of the correlative tephra deposits. These results suggest that no significant rotation occurred between the Osaka–Kyoto, Mie and Niigata areas, but that the Takayama area suffered a clockwise rotation in respect to the other areas during the Quaternary. This rotation might have been caused under an east–west stress field associated with the collision of the Okhotsk Plate with the Eurasia Plate. 相似文献
7.
Miguel Cervantes-Solano Lisa Kapper Avto Goguitchaichvili Vicente Carlos Ruiz-Martínez José Rosas-Elguera Juan Morales Rafael Maciel-Peña Rubén Cejudo-Ruiz 《Studia Geophysica et Geodaetica》2017,61(2):233-248
We present a detailed rock-magnetic and paleomagnetic survey from Autlan volcanic succession in western Mexico. The principal aim of this study is to extend paleomagnetic data from Autlan lavas in order to confirm vertical-axis rotation observed in reconnaissance study and to evaluate long-term variation of the geomagnetic field strength based on existing and global data. The mean inclination (44.7°) is in agreement with the expected inclination for 60 and 70 Ma, as derived from available reference poles for the North American craton. The declination (333.6°), however, is significantly different from those expected, which suggests a statistically significant counterclockwise tectonic rotation ranging between 10° ± 6° and 14° ± 7°. As a measure of paleosecular variation (PSV), we obtained a geomagnetic field dispersion of 9.6° (upper and lower limits: 7.2°–11.9°) in perfect agreement with the previously published PSV compilation of selected Cretaceous data from lavas. The mean virtual dipole moments available for Autlan lavas are about 65% of the present geomagnetic axial dipole but are in reasonably good agreement with other comparable quality determinations between 5 and 90 Ma. This reinforces the hypothesis that low geomagnetic field strengths persisted for the entire Jurassic extending into the Upper Cretaceous. 相似文献
8.
The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed. 相似文献
9.
Transitional VGP paths recorded in sediments cluster into two antipodal preferred longitude bands that tend to lie 90° away from their site longitudes, the latter also being clustered. VGP paths obtained from lava flow sequences, though much fewer, appear not to show these biases, suggesting a rock-magnetic influence on VGP paths recorded in sediments. Inclination shallowing of detrital magnetic remanence, enhanced under low transitional field strengths, is the most likely candidate.
We illustrate the effects of inclination shallowing by applying a simple shallowing model (tan IR = f tan IA, where IA is the inclination of the magnetic remanence and IA is the inclination of the ambient field) with field variation to hypothetical data sets. Shallowing-induced clustering increases as f decreases and becomes extreme as f approaches 0.1.
We have used the model to ‘de-shallow’ the available set of transitional VGP sediment records for various values of f. The probability that the observations arise from inclination shallowing of a uniform random distribution of paths increases as f decreases. When f drops to 0.13 there is a 50% chance of getting at least as much grouping as observed. To decide if inclination shallowing is a dominant factor in the clustering, we need to know whether such extreme shallowing is widespread in sedimentary records under transitional field conditions. Field and laboratory redeposition data are not yet adequate to resolve this question. 相似文献
10.
The archaeomagnetic study of the ceramics from the multilayered archeological monument Ubeda in Spain provided the data on
the geomagnetic field strength in the period of accumulation of cultural deposits. According to the results obtained for the
Ubeda monument of the Bronze Age and the La Motilla Del Azuer multilayer archaeological monument dated to the second millennium
BC, the time interval of accumulation of the Ubeda cultural deposits likely spans from the last quarter of the 19th to 18th
centuries BC. The sharp decrease in the geomagnetic field strength in the 19th century BC. established against the obtained
data is consistent with the archaeomagnetic results for other Eurasian regions and can be used for correlating the ages of
various archeological monuments and stages of culture. 相似文献
11.
12.
A. M. Fetisova R. V. Veselovskiy F. Scholze Yu. P. Balabanov 《Izvestiya Physics of the Solid Earth》2018,54(1):150-162
The results of detailed paleomagnetic studies in seven Upper Permian and Lower Triassic reference sections of East Europe (Middle Volga and Orenburg region) and Central Germany are presented. For each section, the coefficient of inclination shallowing f (King, 1955) is estimated by the Elongation–Inclination (E–I) method (Tauxe and Kent, 2004) and is found to vary from 0.4 to 0.9. The paleomagnetic directions, corrected for the inclination shallowing, are used to calculate the new Late Permian–Early Triassic paleomagnetic pole for the East European Platform (N = 7, PLat = 52.1°, PLong = 155.8°, A95 = 6.6°). Based on this pole, the geocentric axial dipole hypothesis close to the Paleozoic/Mesozoic boundary is tested by the single plate method. The absence of the statistically significant distinction between the obtained pole and the average Permian–Triassic (P–Tr) paleomagnetic pole of the Siberian Platform and the coeval pole of the North American Platform corrected for the opening of the Atlantic (Shatsillo et al., 2006) is interpreted by us as evidence that ~250 Ma the configuration of the magnetic field of the Earth was predominantly dipolar; i.e., the contribution of nondipole components was at most 10% of the main magnetic field. In our opinion, the hypothesis of the nondipolity of the geomagnetic field at the P–Tr boundary, which has been repeatedly discussed in recent decades (Van der Voo and Torsvik, 2001; Bazhenov and Shatsillo, 2010; Veselovskiy and Pavlov, 2006), resulted from disregarding the effect of inclination shallowing in the paleomagnetic determinations from sedimentary rocks of “stable” Europe (the East European platform and West European plate). 相似文献
13.
V. P. Shcherbakov A. V. Khokhlov N. K. Sycheva 《Izvestiya Physics of the Solid Earth》2014,50(2):222-228
The results of numerical modeling of the geomagnetic secular variation by the method of the Giant Gaussian Process (GGP) are presented and compared with the information derived from the presentday databases for paleointensity. The variances of the positions of the virtual geomagnetic pole (VGP) calculated from the synthetic and experimental data (Brunhes epoch, effusive rocks) are nearly similar, which supports the validity of the theoretical model. The average value of the virtual axial geomagnetic dipole (VADM) calculated from the PINT world database on paleointensity and the Sint-2000 model is lower than VADM calculated by the GGP model; at the same time, the estimates based on the archaeomagnetic data give the VADM value slightly above the model prediction. The largest difference is observed in the variances of VADM, which is for all the three databases noticeably higher than the value calculated from the GGP model. Most probably, this is due to the contribution of the neglected measurement errors of VADM. 相似文献
14.
A variety of paleomagnetic data from the Mediterranean region show a strong bias toward shallow inclinations. This pattern of shallow inclinations has been interpreted to be the result of (1) major northward terrane displacement, (2) large nondipole components in the Earth's magnetic field, and (3) systematic inclination flattening of the paleomagnetic directions. Here, we use the observation that, in addition to the well-known variation of magnetic inclination with latitude, the N-S elongation of directional dispersion also varies, being most elongate at the equator and nearly symmetric at the poles. Assuming that inclination shallowing follows the relationship long known from experiment, we invert the inclinations using a range of “flattening factors” to find the elongation/inclination pair consistent with a statistical model for the paleosecular variation. We apply the so-called “elongation/inclination” method to the extensive paleomagnetic data sets from the Miocene sediments of the Calatayud basin (Spain) and the island of Crete (Greece). After correction, the Spanish data are in good agreement with the expected middle Miocene latitude of the region. The data from Crete suggest that it occupied a position in the late Miocene about 275 km north of the predicted location. This is in agreement with the geological and geodynamical models for the east Mediterranean region, which indicate that slab rollback processes in combination with Anatolian push generated southward migration of Crete. The 7.5 million year average displacement rate of Crete estimated by the E/I method is 37 mm/yr to the south, which closely coincides with present-day rates based on global positioning system (GPS) and model measurements. We also show that inappropriate tilt corrections lead to a shallow inclination bias as well, explaining that observed in studies of lava flows of the region. We conclude that the east Mediterranean inclination anomaly is caused by sedimentary inclination error and not by a persistent octupolar contribution to the geomagnetic field, or northward transport. 相似文献
15.
Compilations of historical observations, archaeomagnetic data from ancient fireplaces and palaemagetic results from short cores of sediment from lakes in southeastern Australia, particularly Lake Keilambete, provide a detailed record of the geomagnetic secular variation during the last 3000 years. The independent sets of data are in good agreement if the radiocarbon time scale for the lacustrine record is about 450 years too old. The error is attributed to systematic incorporation of ancient carbon into the lake floor sediments, mainly through erosion of sediment on the crater walls at times of low water level. A significant lag between deposition and the acquisition of stable magnetic remanence is ruled out. Inclination has been abnormally steep during the last 500 years but remained fairly close to the axial dipole field value prior to that. During the last 1000 years the predominant sense of looping of the magnetic vector corresponds to westward drift of the nondipole field. Secular variations on a time scale of ～ 100 years can be resolved by the lacustrine record. 相似文献
16.
S. P. Burlatskaya S. F. Burlatsky A. F. Burlatsky S. A. Didenko 《Izvestiya Physics of the Solid Earth》2006,42(3):207-224
The purpose of archaeomagnetic research is to investigate the structure of the geomagnetic field and its evolution. This paper is a study of this type. In our preceding studies, we divided the geomagnetic field into dipole and nondipole components. It was then shown that the dipole component consists of the predominant 1200-yr variation and the remainder δ. The δ variation is the subject of this paper. Detailed study and comparison of the characteristic features of two 1200-yr variations (the dipole and δ variations) in both the declination and inclination indicates that, according to most of their features, they can be assigned to different types of waves, namely, traveling waves (the dipole variation) and standing waves (the δ variation). Successive averaging in time and space yielded averaged data on δI and δD not only for various parts of the world (Europe, Asia, and America) but also for the western and eastern hemispheres. 相似文献
17.
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. 相似文献
18.
第七代国际地磁参考场的检验与评价 总被引：4，自引：1，他引：3
本文对国际地磁和高空物理学会推荐的第七代国际地磁参考场进行了检验和评价。评价工作是通过１９６０～１９９５年（５年间隔）中国地磁台的观测数据;对中国地区复测点的测量数据;中国地区三阶泰乐多项式模型与第七代国际地磁参考场模型进行了比较,求得了平均差和标准偏差。并以１９９０年代为例,做出了１９９０年代各个地磁要素两个模型计算值之间的差值图,图上显示出这些差值的异常分布,这结异常是来自地壳源,比较结果,可 相似文献
19.
运用 Thellier 逐步热退磁法,主要测定了我国四川一些地区新石器时期至明、清各朝代的地球磁场总强度值。本文结果表明,在过去5000多年里,该地区地球磁场的总强度随时间呈较大幅度的变化。将该地区与我国其它相关地区地球磁场总强度的长期变化曲线进行对比研究的结果表明:变化的总趋势大致可比,但最高值出现的时间不同.从过去四千年间,新疆、四川、广东、福建及洛阳一些地区的地球磁场强度变化曲线中最高峰和跨时千余年的"M"型变化中低峰出现的时间推得的滞后速度在0.01°-0.03°/a 之间。 相似文献
20.
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. 相似文献