Il contributo della Georgia alla costruzione di una Curva di Variazione geomagnetica Secolare per il Caucaso e la regione Circum-Mediterranea

Responsabili di progetto

Claudia Principe, Marina Devidze

Accordo

GEORGIA - SRNSF - Shota Rustaveli National Science Foundation

Bando

CNR/SRNSF 2012-2013

Dipartimento

Terra e Ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

Proposta di ricerca

Archaeometric dating techniques are nowadays commonly applied as routine tools in archaeological studies. Quite a number of techniques are available and the choice of the most suitable depends on several factors, as the typology of materials studied, their preservation, their absolute chronology and finally the accuracy of the method.
During the last decades, archaeomagnetism has established great progress in reconstructing chronologies of baked sediments, archaeological features and volcanic rocks. The ability to yield absolute ages mainly depends on our knowledge from the past secular variation of the Earth's magnetic field for a given territory, and so on the existence of well-detailed and reliable reference curves [1]. Because direct instrumental measurements of the directional Earth's magnetic field started in Europe in 16th century AD, archaeomagnetic studies which have been carried out on well-dated and undisturbed since firing archaeological structures and volcanic deposits can both contribute to improve our knowledge of the behavior of the past geomagnetic field. For these reasons, archaeomagnetism requires a tighten collaboration between scientists coming from very different specializations such as geophysics, archaeology and volcanology.
Archaeomagnetic analyses reveal the direction and/or the intensity related to the final firing. Because Earth's magnetic field elements -both directional (declination, D and inclination, I) and intensity data (F) -change temporally as well as spatially, different geomagnetic secular variation curves (SVCs) are needed for different sampling localities. Transferring archaeo-magnetic data from the sampling site to a central reference point is commonly performed by the Virtual Geomagnetic Pole (VGP) method. However this process can introduce systematic errors due to the non-dipole components of the main field, and generally their values increase with the relocation distance: that's the reason because SVCs should be constructed using data from a small territory. In a recent work, Casas and Incoronato [2] estimated a medium error on 0.25°/100 km and 100-200 nT/100 km for European area.
SV reference curves are at present available for Europe, including Spain [3], France [4,5], Germany [6], Austria [7], Great Britain [8], Hungary [9], and Bulgaria [10]. In Italy, despite its high number of archaeological excavations, its rich historical background and the great abundance of historical volcanic eruptions, only limited data have been published, even if the first archaeomagnetic investigations were already carried out more than a century ago from Melloni and Folgheraiter [11,12]. Recently, an updated compilation of 74 archaeomagnetic directions carried out on Italian archaeological burnt structures and lavas has been presented by Tema et al. [13]. The most recent attempt of definition of an accurate SVC for italy has been recently made by the members of the italian team [14, 15], by providing archaeomagnetic dating of both volcanic and archaeological Italian sites [14-23].
All SVCs show differences in the database time span, density distribution and methodological approaches followed for their implementation, resulting in different accuracy and precision. For instance, while the French and, Bulgarian SV curves were constructed using the stratified bivariate extension of the Fisher's statistic developed by Le Goff [24, 25], other curves was constructed the dating algorithm developed by Lanos [26] using the hierarchical Bayesian modeling based on roughness penalty, thus determining differences in the age determination, even using the same database.
However the most recent approach to define the SV paths is the realization of regional models able to describe the path of the Earth's magnetic field at the continental scale for territories as large as Europe [27,28]. In addition, another advantage of this approach consists in implementing the SVC each time by referring it to the sampling location, thus avoiding relocation errors.
 
Area of investigation and experience of the scientific teams
Georgia has a great abundance of well characterized archeological sites and it is located in a strategic area to the constraint and completion of the general European SV curve toward the easternmost regions. In addition although, to our knowledge, paleomagnetic studies have been performed for the Georgian territory [29], neither archeomagnetic investigation nor SVC is available for this country.
The members of the Italian team involved in the present project have a long time experience in the techniques for the archeomagnetic dating. On the other hand the members of the Georgian team have long time experience on geophysical methods and archeological exploration.
The collaboration between the italian and georgian group will constitutes the basis for the creation of an independent archeomagnetic laboratory able to provide a new source of high quality data to the developement of larger scale (peri-Mediterranean) SVC. The construction of such a facility will also represent the ideal flywheel for the developement of a tool for the archeological investigation of Georgian territory.
Sampling will be performed using the Modified Thellier Sampling Technique. This technique allows to collect a large quantity of materials with a low risk of movement of fine particles. Generally a total of 12-15 independently oriented samples are taken during sampling works. Pre-analytical treatment of samples will be carried out in Georgia. Measurements will be carried out at IGG-CNR Archaeomagnetic Laboratory in Villa Borbone, Viareggio (Italy).
 
The aim of this program is to produce, by archaeomagnetic studies, an extensive sampling and analyses of fiery structures in Georgia, to contribute to the building of a Georgian SVC and to improuve the Archaeomagnetic data base for Peri-Mediterranean region.
 
References
[1]Phys Earth Planet Int 24 (1981) 89-132; [2] Geophys. J. Int. 169 (2007) 448-454; [3] Geochem. Geophys. Geosyst. 7 (2006); [4] Phys Earth Planet Int 87 (1994) 95-10;  [5] Earth Planet. Int. 131 (2002) 81-89; [6] Geophys J Int 163 (2005) 479-490; [7] Geophys J Int 166 (2006) 91-96; [8] Phys Earth Planet Int 160 (2007) 97-107;[9] J Int 164 (2006) 484-489; [10] Geochem. Geophys. Geosyst. 10 (2009); [11] Memorie dell'Accademia di Scienze di Napoli, 1853, pp. 121-140; [12] J Phys 8 (1899) 660-667;[13] J. Int. 167 (2006) 1160-1171; [14] S Arrighi, 2004, The large sample archaeomagnetic method applied to neapolitan volcanoes and aeolian island, PhD thesis, Università di Pisa, Italia; [15] Journal of Cultural Heritage, 12 (2011), 1-10; [16] EOS vol 90, n.ro 40, 6 oct 2009, 349-350;  [17] Journal Volcanol Geotherm Res, 186, 305-319;[18] M Firmati, C Principe, S Arrighi (2006): L'impianto metallurgico tardo repubblicano di San Bennato all'Isola d'Elba (Rio Marina, LI). AGOGE' Atti della Scuola di Specializzazione in Archeologia, Università di Pisa, III: 301-312, Edizioni PLUS, Pisa; [19] Bull Volcanol, 66, 703-724; [20] Earth Planetary Sci Lett, 211 (2003), 111-124; [21] CR Acad Sci Paris, Earth & Planetary Sciences, 329, 557-564; [22] J Malfatti, 2009, L'archeomagnetismo. Analisi critica del metodo e nuova proposta per una curva di variazione secolare italiana per il primo millennio a.C., Tesi Università di Pisa; [23] J Malfatti, C Principe, S Arrighi, C Arias (2009), L'archeomagnetismo per la datazione delle attività siderurgiche antiche. In F Cambi, F Cavari, C Mascione, MATERIALI DA COSTRUZIONE E PRODUZIONE DEL FERRO -Studi sull'economia populoniese fra periodo etrusco e romanizzazione, Edipuglia, pg. 213-218; [24] Phys Earth Planet Int 93 (1996) 159-190; [25] CR Acad Sci S II 311 (1990) 1191-1198; [26] P Lanos, Bayesian inference of calibration curves: applications to Archaeomagnetism, in: C. Buck, A. Millard (Eds.), Tools for constructing chronologies: crossing interdisciplinary boundaries, vol 177, Springer-Verlag, 2004; [27] Geochem. Geophys. Geosyst. 10 (2009); [28] Archaeometry 51 (2) (2009) 309-322;[29] Quaternary Res 69 (2008) 91-96.

 

Obiettivi della ricerca

General objective: As to our knowledge any SVC nor for the Georgian territory neither for the Caucasus region, is so far available, along with the proposed research we will perform new archeomagnetic measurements to fill the gap of information nowadays existing for the European SVC models toward the easternmost countries. By doing this we will also define the first archeomagnetic SVC for Georgia and the surrounding territory.  An adequate number of known-age fiery structures will be sampled and analysed.
The collaboration between the italian and georgian group will also constitutes the basis for the creation of an independent archeomagnetic laboratory able to provide a new source of high quality data to the developement of larger scale (peri-Mediterranean) SVC in the future and the basis for the establishment of a long-term scientific interxchange between Italy and Georgia.
Tasks for the Georgian Scientific community: (A-First year) Applicability of the European curve(s) to Georgia, by means of the archaeomagnetic analysis of a number of indipendently well dated sites inside the last 8.000 years. (B-Second year) Work focus on a time interval of major interest from the Archaeological point of view, for the building/perfectioning of the Georgian SVC.
Tasks for the Italian Scientific community: To balance the geographical distribution of data inside the general data-base of the Archaeomagnetic data, with Georgian well-dated Archaeological structures, in the time span of the last 8.000 years.  
 

Ultimo aggiornamento: 02/09/2025