Mary Kovatcheva or most frequently Kovacheva (original) (raw)
Papers by Mary Kovatcheva or most frequently Kovacheva
Physics of the Earth and Planetary Interiors
Journal of Geomagnetism and Geoelectricity, Apr 1, 1997
... Studies of Archaeological Samples: Implications for Sample Selection for Paleointensity Deter... more ... Studies of Archaeological Samples: Implications for Sample Selection for Paleointensity Determinations Yulong Cui1, Kenneth L. Verosub1, Andrew P. Roberts1 ... text still appears to be a valid indicator for the predominance of MD grains (Xu and Dunlop, 1995 ... Roberts et al., 1995 ...
Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of... more Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of samples from Neolithic kiln, excavated at Kovatchevo site. Suitability of the materials for obtaining reliable archaeomagnetic results was checked by applying different rock-magnetic experiments. The obtained values of viscosity index and Koeningsberger ratio show favorable stability characteristics of the burnt clay. The main magnetic minerals, identified by Curie temperature analysis through high-temperature behavior of magnetic susceptibility, and three-axes thermal demagnetization of IRM, show the prevailing role of magnetite and Ti-magnetite. However, investigations on the chemical changes occurring during laboratory heating show overall bad thermal stability of the studied materials, which is not good indication concerning palaeointensity determination. Palaeodirection investigation of samples, taken from different parts of the walls and kiln's floor, reveals possible influence of magnetic refraction - higher Inclination values and azymuthal dependence of Declination for the samples from walls; lower Inclination values from floor's samples. Definitive directional results are determined by averaging data for all samples, which are well distributed all over walls and three kiln's floors. For palaeointensity evaluation rock-magnetic studies are carefully considered and strict acception criteria applied. Archaeomagnetic dating of the studied kiln was performed according to the newly developed method (Lanos, 2001). Final dating, taking into account directional and intensity results, gives the most probable time interval of the last kiln's usage between 5712-5571 BC. Dating result is in agreement with archaeological findings for Bulgarian Early Neolithic and most of 14C data available. This study is supported by EU-funded project AARCH, contract No HPRN-CT-2002-00219 and Mission archeologique de la Vallee du Strymon (Centre de Recherches Protohistorique de l'Universite de Paris).
Most important task of archaeomagnetic studies is the construction of the geomagnetic field secul... more Most important task of archaeomagnetic studies is the construction of the geomagnetic field secular variations in the past for a given territory. The obtained reference curves would be precise only when a large number of well-dated archaeological sites from different time periods are included as input data. Sofia Palaeomagnetic laboratory is the first one in the Balkans to accumulate a large number of data spanning the time interval of 3000 BP to 8000 BP. Many archaeological sites in Bulgaria are multilevel settlements with clear stratigraphy. Commonly the prehistoric sites are dated according to the relative chronology, the type of archaeological artifacts found and 14C dates, the latter being not always available. The biggest difficulty is that usually the radiocarbon dates are not well constrained, often contradictory to the vertical stratigraphy. The transformation of conventional 14C dates to absolute dates BC depends a lot on which part of dendrochronological calibration curve...
Physics of the Earth and Planetary Interiors, 1992
The necessity of compilation of worldwide archaeomagnetic results was largely discussed at the sy... more The necessity of compilation of worldwide archaeomagnetic results was largely discussed at the symposium on New Trends in Geomagnetism in Czechoslovakia in the summer of 1988 and at the IAGA meeting in the summer of 1989. However, the elaboration of a given dataset for a determined territory is a continuous process. The newly gathered collections and some specifications of the preliminary datings given necessitate permanent updating of the catalogues. The aim of the present paper is to give the contemporary state of the directional and intensity archaeomagnetic results obtained in the Sofia laboratory over the last 2000 years. The revision and filling up of the dataset for the period 6000-0 years B.C. is now in preparation. Both will be sent to the Archaeomagnetic database (IAGA Working Group 1-5).
Physics of the Earth and Planetary Interiors, 2007
Archaeomagnetic results are presented from a series of burnt structures at the Thracian site of H... more Archaeomagnetic results are presented from a series of burnt structures at the Thracian site of Halka Bunar. Archaeointensity and archaeodirectional studies were undertaken on three kilns from a pottery production complex. This has been dated to the late 4th and early 3rd century b.c. (325-280 b.c.) based on coins found associated with the kilns [Tonkova, M., 2003. Newly discovered Thracian Centre of the Early Hellenistic Age at the Spring "Halka Bunar" in the Land of C. Gorno Belevo. Annuary of the Institute of Archaeology with Museum. Bulgarian Academy Sci. 2, 148-196 (in Bulgarian)]. This data provides a new point for the Bulgarian archaeomagnetic curve (Dec: 348.70 ± 5.79, Inc: 62.20 ± 2.70, and Fa: 77.23 ± 2.17 T). The kilns are thought to have been used for producing different types of pottery in a range of heating atmospheres and at different temperatures. Therefore, special attention was paid to the magnetic mineralogy of the samples and its effect on the palaeodata. Kiln 3, orange clay samples were dominated by fine to ultra-fine grained single domain and superparamagnetic magnetite, with a small proportion of haematite. The samples were heated in a high temperature oxidising environment. Kiln 2 was probably used to make grey ware pottery. The samples are light grey and were dominated by stable single domain magnetite formed by high temperature heating in a more reducing environment. Kiln 4, mottled samples consisted of a variable mineralogy showing characteristics of both Kiln 2 and Kiln 3 samples. It was probably used to make traditional, mottled, Thracian ware pottery and was heated to lower temperatures in a mixed environment of heating. Samples heated in an oxidising environment gave more reliable Thellier results than samples heated in a reducing environment in antiquity, as the latter altered heavily on reheating. A fourth kiln and a destruction feature from different trenches than the kiln complex were also investigated to establish their age. Archaeodirectional data was not recoverable from these two structures due to post-burning disturbance. The mean archaeointensity from Kiln 5 (mean 78.0 ± 1.7 T) is consistent with that from the main kiln complex (mean 77.23 ± 2.17 T) and is therefore considered to be contemporary. It was probably not used to make pottery. The destruction feature records much lower archaeointensity values (mean 65.1 ± 1.1 T). When this value is compared to the existing reference points of the Bulgarian database it suggests this feature is younger than the kilns (250-140 b.c.). Multiple age use of the site is therefore confirmed with a main period of occupation in the late 4th and early 3rd century b.c. and another phase of occupation in the mid 3rd to mid 2nd century b.c.
Studia Geophysica Et Geodaetica, 2001
Rock magnetic investigations of archaeological materials of burnt clay from Eneolithic ovens (~45... more Rock magnetic investigations of archaeological materials of burnt clay from Eneolithic ovens (~4500 years BC) showed particular changes with time in the magnetic mineralogy of samples, stored under normal conditions. Our results indicate that well-burnt clay from the archaeological materials contains a significant amount of very fine magnetic grains, which could notably influence the rock magnetic properties and behavior at
Archaeomagnetism is an interdisciplinary branch of geophysics. It is the only approach that exami... more Archaeomagnetism is an interdisciplinary branch of geophysics. It is the only approach that examines the variation of geomagnetic field elements in the past. The physical basis of the method is the capability of the fired clay to preserve information about the direction and intensity of the Earth's magnetic field in the place and time of its last burning. The information
Earth, Planets and Space, 2009
The effect of magnetic anisotropy on the palaeointensity results has been evaluated in different ... more The effect of magnetic anisotropy on the palaeointensity results has been evaluated in different materials, including samples from archaeological structures of various ages, such as baked clay from prehistoric domestic ovens or pottery kilns, burnt soil from ancient fires, and bricks and bricks or tiles used in the kiln’s construction. The remanence anisotropy was estimated by the thermoremanent (TRM) anisotropy tensor and isothermal remanence (IRM) tensor methods. The small anisotropy effect (less than 5%) observed in the palaeointensity results of baked clay from the relatively thin prehistoric oven’s floors estimated previously through IRM anisotropy was confirmed by TRM anisotropy of this material. The new results demonstrate the possibility of using IRM anisotropy evaluation to correct baked clay palaeointensity data instead of the more difficult to determine TRM anisotropy ellipsoid. This is not always the case for the palaeointensity results from bricks and tiles. The anisotr...
Journal of Radioanalytical and Nuclear Chemistry - J RADIOANAL NUCL CHEM, 2001
Archaeomagnetic studies in Bulgaria have a long history and the well established secular variatio... more Archaeomagnetic studies in Bulgaria have a long history and the well established secular variation curves of the three elements of the ancient geomagnetic field (declination, inclination and intensity) for the last 8000 years enable the dating of archaeological features of burnt clay, independently of other methods. The determination of ancient palaeointensity is the most difficult characteristic and requires very cautious evaluation of the suitability of the burnt clay material. The present paper is an overview of the methodological progress in studying the suitability of the materials for archaeomagnetic investigations. The main rock-magnetic methods and summary of the most common results are presented involving the archaeomagnetic practice in the palaeomagnetic laboratory in Sofia. In addition, supplementary information obtained by magnetic measurements, which can be helpful for archaeology, are discussed. An example of archaeomagnetic dating procedure is also presented.
Surveys in Geophysics, 1994
The archaeomagnetic determinations obtained from the collections of archaeological materials, dat... more 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.
Studia Geophysica et Geodaetica, 2000
A common practice in archaeomagnetic studies in many laboratories is the impregnation of the mate... more A common practice in archaeomagnetic studies in many laboratories is the impregnation of the material with water glass (siliceous gel) in order to achieve better consolidation before cutting. The purpose of this study is to establish if and how the presence of water glass in the burnt clay material affects its magnetic properties during heating. We describe experiments designed to monitor the alterations in isothermal remanence and magnetic susceptibility for two sets of specimens-non-impregnated and impregnated with water glass. Our results show that water glass can cause considerable changes in magnetic susceptibility, but the remanent magnetization is not influenced significantly.
Physics of the Earth and Planetary Interiors, 2007
The goal of the paper is to determine palaeointensity from the archaeological sites mentioned abo... more The goal of the paper is to determine palaeointensity from the archaeological sites mentioned above, as well as to compare the values obtained in different laboratories. Palaeointensity experiments were mainly carried out at the Division of Geophysics, University of Helsinki and at the Palaeomagnetic Laboratory of the Geophysical Institute in Sofia. Additionally, microwave palaeointensity determinations on few sister specimens from Helsinki bricks and from Drustur kiln were performed in Liverpool. Large amount of rock-magnetic studies accompanies the work in order to find possible explanations for the acceptance or failure of palaeointensity experiments. The encountered difficulties in obtaining reliable palaeointensity results are discussed and show a still incomplete state of art for determination of this important ancient geomagnetic field characteristic. The accepted new palaeointensity evaluations for different time and space will partly fill up considerable gaps in European palaeointensity databases. Geophysical inference is demonstrated on the basis of virtual axial dipole moment calculated from the new palaeointensity results and its relationship with the CALS7K.2 model calculation and the observatory measurements for the corresponding territories.
Physics of the Earth and Planetary Interiors, 1990
The paper reports the first paleomagnetic study of a Black Sea Quaternary sediment core made by a... more The paper reports the first paleomagnetic study of a Black Sea Quaternary sediment core made by a Bulgarian research group. The experimental results show an important difference in magnetic behaviour between the samples from the Holocene part and those from the Pleistocene part of the core. Suggestions are made for the character of the remanent magnetization and the main carriers
Physics of the Earth and Planetary Interiors, 2004
Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of... more Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of samples from Neolithic kiln, excavated at Kovatchevo site. Suitability of the materials for obtaining reliable archaeomagnetic results was checked by applying different rock-magnetic experiments. The obtained values of viscosity index and Koeningsberger ratio show favorable stability characteristics of the burnt clay. The main magnetic minerals, identified by Curie temperature analysis through high-temperature behavior of magnetic susceptibility, and three-axes thermal demagnetization of IRM, show the prevailing role of magnetite and Ti-magnetite. However, investigations on the chemical changes occurring during laboratory heating show overall bad thermal stability of the studied materials, which is not good indication concerning palaeointensity determination. Palaeodirection investigation of samples, taken from different parts of the walls and kiln's floor, reveals possible influence of magnetic refraction - higher Inclination values and azymuthal dependence of Declination for the samples from walls; lower Inclination values from floor's samples. Definitive directional results are determined by averaging data for all samples, which are well distributed all over walls and three kiln's floors. For palaeointensity evaluation rock-magnetic studies are carefully considered and strict acception criteria applied. Archaeomagnetic dating of the studied kiln was performed according to the newly developed method (Lanos, 2001). Final dating, taking into account directional and intensity results, gives the most probable time interval of the last kiln's usage between 5712-5571 BC. Dating result is in agreement with archaeological findings for Bulgarian Early Neolithic and most of 14C data available. This study is supported by EU-funded project AARCH, contract No HPRN-CT-2002-00219 and Mission archeologique de la Vallee du Strymon (Centre de Recherches Protohistorique de l'Universite de Paris).
Physics of the Earth and Planetary Interiors, 1997
In 1992 (Kovacheva, 1992) we published the updated archaeomagnetic results from Bulgaria for the ... more In 1992 (Kovacheva, 1992) we published the updated archaeomagnetic results from Bulgaria for the last 2000 years where it was mentioned that the compilation of data is a continuous process of accumulation of new data and revision of the previous ones. This is especially true for the old intensity studies considering the newly obtained experimental results of rock magnetic studies
Physics of the Earth and Planetary Interiors, 1992
An assessment of archaeomagnetic intensities from Greek and Bulgarian data sets during the last 2... more An assessment of archaeomagnetic intensities from Greek and Bulgarian data sets during the last 2000 years indicates sharp changes in their variation. Particular emphasis is given to the reliability of these data and the results are discussed in terms of a latitude effect.
Physics and Chemistry of the Earth, Parts A/B/C, 2008
Archaeomagnetic palaeodirectional and palaeointensity results are presented from a domestic oven ... more Archaeomagnetic palaeodirectional and palaeointensity results are presented from a domestic oven at the mediaeval site of Zlatna Livada. Archaeological evidence suggests that the site was occupied in the 11th or 12th C. AD, with the oven dating to the beginning of this period. The samples are dominated by magnetite and maghaemite. In some samples thermally unstable maghaemite occurs with unblocking temperatures between 300°C and 400°C, while in others maghaemite is stable to inversion until >600°C. The mineral magnetic analyses, Thellier results and sample heterogeneity suggest that the oven was not heated to a very high or consistent temperature in antiquity (<320-<400°C). Hysteresis measurements show a mixture of single and multi-domain grains, which may account for the variability in the success of the Thellier experiments. Water glass, the material used to physically stabilize unconsolidated samples, does not appear to react with the samples' mineralogy until above 500°C, and thus does not affect the Thellier results. The oven has a mean palaeointensity determination of 72.13 lT, a mean declination of 15.8 o and a mean inclination of 61.9 o. The archaeomagnetic age estimate for the site using all three parameters is between 826 and 1004 AD and using only palaeodirectional data is 777-967 AD. Based on these archaeomagnetic age assessments and the archaeological evidence, the site is best dated to the very end of the 10th C. AD or first few years of the 11th C. AD. This confirms that the oven dates to the early period of site use, although the date is perhaps slightly younger than expected. This paper highlights a number of problems encountered during archaeomagnetic studies and emphasises the need for more reference curve data to increase the precision of the dating method, particularly during the mediaeval period in Bulgaria.
Physics of the Earth and Planetary Interiors
Journal of Geomagnetism and Geoelectricity, Apr 1, 1997
... Studies of Archaeological Samples: Implications for Sample Selection for Paleointensity Deter... more ... Studies of Archaeological Samples: Implications for Sample Selection for Paleointensity Determinations Yulong Cui1, Kenneth L. Verosub1, Andrew P. Roberts1 ... text still appears to be a valid indicator for the predominance of MD grains (Xu and Dunlop, 1995 ... Roberts et al., 1995 ...
Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of... more Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of samples from Neolithic kiln, excavated at Kovatchevo site. Suitability of the materials for obtaining reliable archaeomagnetic results was checked by applying different rock-magnetic experiments. The obtained values of viscosity index and Koeningsberger ratio show favorable stability characteristics of the burnt clay. The main magnetic minerals, identified by Curie temperature analysis through high-temperature behavior of magnetic susceptibility, and three-axes thermal demagnetization of IRM, show the prevailing role of magnetite and Ti-magnetite. However, investigations on the chemical changes occurring during laboratory heating show overall bad thermal stability of the studied materials, which is not good indication concerning palaeointensity determination. Palaeodirection investigation of samples, taken from different parts of the walls and kiln's floor, reveals possible influence of magnetic refraction - higher Inclination values and azymuthal dependence of Declination for the samples from walls; lower Inclination values from floor's samples. Definitive directional results are determined by averaging data for all samples, which are well distributed all over walls and three kiln's floors. For palaeointensity evaluation rock-magnetic studies are carefully considered and strict acception criteria applied. Archaeomagnetic dating of the studied kiln was performed according to the newly developed method (Lanos, 2001). Final dating, taking into account directional and intensity results, gives the most probable time interval of the last kiln's usage between 5712-5571 BC. Dating result is in agreement with archaeological findings for Bulgarian Early Neolithic and most of 14C data available. This study is supported by EU-funded project AARCH, contract No HPRN-CT-2002-00219 and Mission archeologique de la Vallee du Strymon (Centre de Recherches Protohistorique de l'Universite de Paris).
Most important task of archaeomagnetic studies is the construction of the geomagnetic field secul... more Most important task of archaeomagnetic studies is the construction of the geomagnetic field secular variations in the past for a given territory. The obtained reference curves would be precise only when a large number of well-dated archaeological sites from different time periods are included as input data. Sofia Palaeomagnetic laboratory is the first one in the Balkans to accumulate a large number of data spanning the time interval of 3000 BP to 8000 BP. Many archaeological sites in Bulgaria are multilevel settlements with clear stratigraphy. Commonly the prehistoric sites are dated according to the relative chronology, the type of archaeological artifacts found and 14C dates, the latter being not always available. The biggest difficulty is that usually the radiocarbon dates are not well constrained, often contradictory to the vertical stratigraphy. The transformation of conventional 14C dates to absolute dates BC depends a lot on which part of dendrochronological calibration curve...
Physics of the Earth and Planetary Interiors, 1992
The necessity of compilation of worldwide archaeomagnetic results was largely discussed at the sy... more The necessity of compilation of worldwide archaeomagnetic results was largely discussed at the symposium on New Trends in Geomagnetism in Czechoslovakia in the summer of 1988 and at the IAGA meeting in the summer of 1989. However, the elaboration of a given dataset for a determined territory is a continuous process. The newly gathered collections and some specifications of the preliminary datings given necessitate permanent updating of the catalogues. The aim of the present paper is to give the contemporary state of the directional and intensity archaeomagnetic results obtained in the Sofia laboratory over the last 2000 years. The revision and filling up of the dataset for the period 6000-0 years B.C. is now in preparation. Both will be sent to the Archaeomagnetic database (IAGA Working Group 1-5).
Physics of the Earth and Planetary Interiors, 2007
Archaeomagnetic results are presented from a series of burnt structures at the Thracian site of H... more Archaeomagnetic results are presented from a series of burnt structures at the Thracian site of Halka Bunar. Archaeointensity and archaeodirectional studies were undertaken on three kilns from a pottery production complex. This has been dated to the late 4th and early 3rd century b.c. (325-280 b.c.) based on coins found associated with the kilns [Tonkova, M., 2003. Newly discovered Thracian Centre of the Early Hellenistic Age at the Spring "Halka Bunar" in the Land of C. Gorno Belevo. Annuary of the Institute of Archaeology with Museum. Bulgarian Academy Sci. 2, 148-196 (in Bulgarian)]. This data provides a new point for the Bulgarian archaeomagnetic curve (Dec: 348.70 ± 5.79, Inc: 62.20 ± 2.70, and Fa: 77.23 ± 2.17 T). The kilns are thought to have been used for producing different types of pottery in a range of heating atmospheres and at different temperatures. Therefore, special attention was paid to the magnetic mineralogy of the samples and its effect on the palaeodata. Kiln 3, orange clay samples were dominated by fine to ultra-fine grained single domain and superparamagnetic magnetite, with a small proportion of haematite. The samples were heated in a high temperature oxidising environment. Kiln 2 was probably used to make grey ware pottery. The samples are light grey and were dominated by stable single domain magnetite formed by high temperature heating in a more reducing environment. Kiln 4, mottled samples consisted of a variable mineralogy showing characteristics of both Kiln 2 and Kiln 3 samples. It was probably used to make traditional, mottled, Thracian ware pottery and was heated to lower temperatures in a mixed environment of heating. Samples heated in an oxidising environment gave more reliable Thellier results than samples heated in a reducing environment in antiquity, as the latter altered heavily on reheating. A fourth kiln and a destruction feature from different trenches than the kiln complex were also investigated to establish their age. Archaeodirectional data was not recoverable from these two structures due to post-burning disturbance. The mean archaeointensity from Kiln 5 (mean 78.0 ± 1.7 T) is consistent with that from the main kiln complex (mean 77.23 ± 2.17 T) and is therefore considered to be contemporary. It was probably not used to make pottery. The destruction feature records much lower archaeointensity values (mean 65.1 ± 1.1 T). When this value is compared to the existing reference points of the Bulgarian database it suggests this feature is younger than the kilns (250-140 b.c.). Multiple age use of the site is therefore confirmed with a main period of occupation in the late 4th and early 3rd century b.c. and another phase of occupation in the mid 3rd to mid 2nd century b.c.
Studia Geophysica Et Geodaetica, 2001
Rock magnetic investigations of archaeological materials of burnt clay from Eneolithic ovens (~45... more Rock magnetic investigations of archaeological materials of burnt clay from Eneolithic ovens (~4500 years BC) showed particular changes with time in the magnetic mineralogy of samples, stored under normal conditions. Our results indicate that well-burnt clay from the archaeological materials contains a significant amount of very fine magnetic grains, which could notably influence the rock magnetic properties and behavior at
Archaeomagnetism is an interdisciplinary branch of geophysics. It is the only approach that exami... more Archaeomagnetism is an interdisciplinary branch of geophysics. It is the only approach that examines the variation of geomagnetic field elements in the past. The physical basis of the method is the capability of the fired clay to preserve information about the direction and intensity of the Earth's magnetic field in the place and time of its last burning. The information
Earth, Planets and Space, 2009
The effect of magnetic anisotropy on the palaeointensity results has been evaluated in different ... more The effect of magnetic anisotropy on the palaeointensity results has been evaluated in different materials, including samples from archaeological structures of various ages, such as baked clay from prehistoric domestic ovens or pottery kilns, burnt soil from ancient fires, and bricks and bricks or tiles used in the kiln’s construction. The remanence anisotropy was estimated by the thermoremanent (TRM) anisotropy tensor and isothermal remanence (IRM) tensor methods. The small anisotropy effect (less than 5%) observed in the palaeointensity results of baked clay from the relatively thin prehistoric oven’s floors estimated previously through IRM anisotropy was confirmed by TRM anisotropy of this material. The new results demonstrate the possibility of using IRM anisotropy evaluation to correct baked clay palaeointensity data instead of the more difficult to determine TRM anisotropy ellipsoid. This is not always the case for the palaeointensity results from bricks and tiles. The anisotr...
Journal of Radioanalytical and Nuclear Chemistry - J RADIOANAL NUCL CHEM, 2001
Archaeomagnetic studies in Bulgaria have a long history and the well established secular variatio... more Archaeomagnetic studies in Bulgaria have a long history and the well established secular variation curves of the three elements of the ancient geomagnetic field (declination, inclination and intensity) for the last 8000 years enable the dating of archaeological features of burnt clay, independently of other methods. The determination of ancient palaeointensity is the most difficult characteristic and requires very cautious evaluation of the suitability of the burnt clay material. The present paper is an overview of the methodological progress in studying the suitability of the materials for archaeomagnetic investigations. The main rock-magnetic methods and summary of the most common results are presented involving the archaeomagnetic practice in the palaeomagnetic laboratory in Sofia. In addition, supplementary information obtained by magnetic measurements, which can be helpful for archaeology, are discussed. An example of archaeomagnetic dating procedure is also presented.
Surveys in Geophysics, 1994
The archaeomagnetic determinations obtained from the collections of archaeological materials, dat... more 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.
Studia Geophysica et Geodaetica, 2000
A common practice in archaeomagnetic studies in many laboratories is the impregnation of the mate... more A common practice in archaeomagnetic studies in many laboratories is the impregnation of the material with water glass (siliceous gel) in order to achieve better consolidation before cutting. The purpose of this study is to establish if and how the presence of water glass in the burnt clay material affects its magnetic properties during heating. We describe experiments designed to monitor the alterations in isothermal remanence and magnetic susceptibility for two sets of specimens-non-impregnated and impregnated with water glass. Our results show that water glass can cause considerable changes in magnetic susceptibility, but the remanent magnetization is not influenced significantly.
Physics of the Earth and Planetary Interiors, 2007
The goal of the paper is to determine palaeointensity from the archaeological sites mentioned abo... more The goal of the paper is to determine palaeointensity from the archaeological sites mentioned above, as well as to compare the values obtained in different laboratories. Palaeointensity experiments were mainly carried out at the Division of Geophysics, University of Helsinki and at the Palaeomagnetic Laboratory of the Geophysical Institute in Sofia. Additionally, microwave palaeointensity determinations on few sister specimens from Helsinki bricks and from Drustur kiln were performed in Liverpool. Large amount of rock-magnetic studies accompanies the work in order to find possible explanations for the acceptance or failure of palaeointensity experiments. The encountered difficulties in obtaining reliable palaeointensity results are discussed and show a still incomplete state of art for determination of this important ancient geomagnetic field characteristic. The accepted new palaeointensity evaluations for different time and space will partly fill up considerable gaps in European palaeointensity databases. Geophysical inference is demonstrated on the basis of virtual axial dipole moment calculated from the new palaeointensity results and its relationship with the CALS7K.2 model calculation and the observatory measurements for the corresponding territories.
Physics of the Earth and Planetary Interiors, 1990
The paper reports the first paleomagnetic study of a Black Sea Quaternary sediment core made by a... more The paper reports the first paleomagnetic study of a Black Sea Quaternary sediment core made by a Bulgarian research group. The experimental results show an important difference in magnetic behaviour between the samples from the Holocene part and those from the Pleistocene part of the core. Suggestions are made for the character of the remanent magnetization and the main carriers
Physics of the Earth and Planetary Interiors, 2004
Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of... more Archaeomagnetic investigation of direction and palaeointensity was carried out on a collection of samples from Neolithic kiln, excavated at Kovatchevo site. Suitability of the materials for obtaining reliable archaeomagnetic results was checked by applying different rock-magnetic experiments. The obtained values of viscosity index and Koeningsberger ratio show favorable stability characteristics of the burnt clay. The main magnetic minerals, identified by Curie temperature analysis through high-temperature behavior of magnetic susceptibility, and three-axes thermal demagnetization of IRM, show the prevailing role of magnetite and Ti-magnetite. However, investigations on the chemical changes occurring during laboratory heating show overall bad thermal stability of the studied materials, which is not good indication concerning palaeointensity determination. Palaeodirection investigation of samples, taken from different parts of the walls and kiln's floor, reveals possible influence of magnetic refraction - higher Inclination values and azymuthal dependence of Declination for the samples from walls; lower Inclination values from floor's samples. Definitive directional results are determined by averaging data for all samples, which are well distributed all over walls and three kiln's floors. For palaeointensity evaluation rock-magnetic studies are carefully considered and strict acception criteria applied. Archaeomagnetic dating of the studied kiln was performed according to the newly developed method (Lanos, 2001). Final dating, taking into account directional and intensity results, gives the most probable time interval of the last kiln's usage between 5712-5571 BC. Dating result is in agreement with archaeological findings for Bulgarian Early Neolithic and most of 14C data available. This study is supported by EU-funded project AARCH, contract No HPRN-CT-2002-00219 and Mission archeologique de la Vallee du Strymon (Centre de Recherches Protohistorique de l'Universite de Paris).
Physics of the Earth and Planetary Interiors, 1997
In 1992 (Kovacheva, 1992) we published the updated archaeomagnetic results from Bulgaria for the ... more In 1992 (Kovacheva, 1992) we published the updated archaeomagnetic results from Bulgaria for the last 2000 years where it was mentioned that the compilation of data is a continuous process of accumulation of new data and revision of the previous ones. This is especially true for the old intensity studies considering the newly obtained experimental results of rock magnetic studies
Physics of the Earth and Planetary Interiors, 1992
An assessment of archaeomagnetic intensities from Greek and Bulgarian data sets during the last 2... more An assessment of archaeomagnetic intensities from Greek and Bulgarian data sets during the last 2000 years indicates sharp changes in their variation. Particular emphasis is given to the reliability of these data and the results are discussed in terms of a latitude effect.
Physics and Chemistry of the Earth, Parts A/B/C, 2008
Archaeomagnetic palaeodirectional and palaeointensity results are presented from a domestic oven ... more Archaeomagnetic palaeodirectional and palaeointensity results are presented from a domestic oven at the mediaeval site of Zlatna Livada. Archaeological evidence suggests that the site was occupied in the 11th or 12th C. AD, with the oven dating to the beginning of this period. The samples are dominated by magnetite and maghaemite. In some samples thermally unstable maghaemite occurs with unblocking temperatures between 300°C and 400°C, while in others maghaemite is stable to inversion until >600°C. The mineral magnetic analyses, Thellier results and sample heterogeneity suggest that the oven was not heated to a very high or consistent temperature in antiquity (<320-<400°C). Hysteresis measurements show a mixture of single and multi-domain grains, which may account for the variability in the success of the Thellier experiments. Water glass, the material used to physically stabilize unconsolidated samples, does not appear to react with the samples' mineralogy until above 500°C, and thus does not affect the Thellier results. The oven has a mean palaeointensity determination of 72.13 lT, a mean declination of 15.8 o and a mean inclination of 61.9 o. The archaeomagnetic age estimate for the site using all three parameters is between 826 and 1004 AD and using only palaeodirectional data is 777-967 AD. Based on these archaeomagnetic age assessments and the archaeological evidence, the site is best dated to the very end of the 10th C. AD or first few years of the 11th C. AD. This confirms that the oven dates to the early period of site use, although the date is perhaps slightly younger than expected. This paper highlights a number of problems encountered during archaeomagnetic studies and emphasises the need for more reference curve data to increase the precision of the dating method, particularly during the mediaeval period in Bulgaria.