Archaeomagnetic study and thermoluminescence dating of Protobyzantine kilns (Megali Kypsa, North Greece)

Journal of Archaeological Science: Reports 2 (2015) 156–168

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Archaeomagnetic study and thermoluminescence dating of Protobyzantine kilns (Megali Kypsa, North Greece) D. Kondopoulou a, E. Aidona a,⁎, N. Ioannidis a, G.S. Polymeris b, S. Tsolakis c a b c

Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece Institute of Nuclear Sciences, University of Ankara, 06100 Beşevler, Ankara, Turkey 10th Ephorate of Byzantine Antiquities, Thessaloniki, Greece

a r t i c l e

i n f o

Article history: Received 2 August 2014 Received in revised form 4 December 2014 Accepted 12 January 2015 Available online 24 January 2015 Keywords: Archaeomagnetism Thermoluminescence dating Protobyzantine kiln complex Greece

a b s t r a c t The large Protobyzantine settlement of Megali Kypsa was excavated at the NW part of Chalkidiki peninsula (North Greece). Among the numerous residential buildings a big ceramic complex with twelve kilns was unearthed. Nine of the kilns were preserved fairly well and the archaeological investigation suggested a large ceramic production for local use and exportation. The three best preserved kilns were sampled for an archaeomagnetic study, while numerous TL dating results in combination with archaeological information constrained the last use of the kilns from the end of the 4th to the middle of the 5th century AD. Rock magnetic analyses have been performed on pilot samples and identified magnetite as the main carrier of the natural remanent magnetisation. The samples were subjected to both alternating field and thermal demagnetisation providing reliable directions. Intensities were calculated with the Triaxe protocol and yielded a mean value of 61.2 ± 1.8 μΤ. The obtained results are compared with regional and global geomagnetic field models (SCHA.DIF.3K and ARCH.3K). Our study provides 3 new full-vector data, improving the resolution of the Greek secular variation curve for this poorly documented period. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction The number of archaeomagnetic studies is nowadays increasing worldwide, with a particular flourishing in Europe. Constant progress during the last decades resulted in several regional databases and Secular Variation Curves (SVCs) for directions (Gallet et al., 2002; Schnepp and Lanos, 2005; Gómez-Paccard et al., 2006; Márton and Ferencz, 2006; Tema et al., 2006; Zananiri et al., 2007), as well as for intensities (Kovacheva et al., 1998, 2009; Genevey et al., 2013; Gómez-Paccard et al., 2008, 2012; Tema et al., 2013b). The use of both archaeodirections and archaeointensities enriched all databases and, consequently, geomagnetic field models (GMF) have been substantially improved on regional (Pavón-Carrasco et al., 2009, 2010) as well as on global scale (e.g. Korte et al., 2005; Genevey et al., 2008; Donadini et al., 2009). Despite this progress, the temporal and spatial coverage of data used to build the reference curves remains uneven, especially at the country scale (Genevey et al., 2008; Tema and Kondopoulou, 2011). Such curves are also available for Greece, both for intensities (De Marco et al., 2008; Tema et al., 2012; Fanjat et al., 2013) and directions, which were recently compiled by De Marco et al., 2014. Intensity data cover the last 8000 years, while directions extend within the last

⁎ Corresponding author. E-mail address: [email protected] (E. Aidona).

http://dx.doi.org/10.1016/j.jasrep.2015.01.007 2352-409X/© 2015 Elsevier Ltd. All rights reserved.

4500 years only. Nevertheless, data from older periods are emerging as well (Aidona and Kondopoulou, 2012). Wider time ranges can be covered by combining datasets from the broader Balkan area (Tema and Kondopoulou, 2011), however, the Greek SVC need still new data from specific periods where a lack of adequate, well-dated, structures hampers further archaeomagnetic research. In the period corresponding to the one of the present study only eight directional and twelve intensity data are available between 415 and 565 AD. Therefore accumulating new, high-quality, data remains an important target. The number of cooperations between geophysicists and archeologists is increasing; however archaeomagnetic dating remains the most common application of archaeomagnetism. Successful archaeomagnetic dating highly depends on the quality of the available reference curves, and consequently on the possibility to accurately study relevant structures dated with independent methods. Several archaeometric techniques offer reliable dating tools but one of them, namely thermoluminescence (TL) presents an important advantage for archaeomagnetic studies: it can be applied, under certain conditions, to the same material, in order to date the same event that is the last firing of the studied object or structure. There are two prerequisites for such application: the degree of heating should be sufficiently high and the material should have remained undisturbed since cooling down from the last firing (Aitken, 1985). If these are fulfilled, the method offers a valuable opportunity to obtain reliable reference points for the completion of the Secular Variation Curves.

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In the present archaeomagnetic study we investigate two pottery kilns (SAN6, SAN10) excavated within a spacious, archaeologically fairly well-dated, Protobyzantine settlement, situated at the western part of Kassandra, the first of the three fingers of Chalkidiki Peninsula in North Greece (Fig. 1). The TL method has also been applied in order to date as accurately as possible the end of the settlement activity. A third kiln (SAN8) of the same site, previously studied by Aidona et al. (2010), has also been dated with TL, as well as a fourth one (SAN5), for cross checking reasons. On the latter one no archaeomagnetic study was performed, due to its very poor preservation. The combined archaeological and TL dates from the two kilns (SAN6, SAN10) provide two new, high-quality, full vector reference points for the Protobyzantine period in Greece, while the new TL age assigned to the third, published one (SAN8), improves the dating precision. 2. Site description and sampling The settlement of Megali Kypsa is located at the NW part of Kassandra, the western finger of Chalkidiki peninsula, in the immediate vicinity of the Thermaikos Gulf. (Fig. 1a). Kassandra is largely formed of Neogene sediments and older rocks crop out only at its southernmost tip. These older rocks include Upper Jurassic ophiolitic material associated with Upper Jurassic limestones, Cretaceous black limestones and calcareous schists and sandstones. Eocene sediments occur also along the southern part of the west coast (Kockel et al., 1977; Bornovas and Rondogianni-Tsiambaou, 1983). The Neogene sequence, from bottom to top, consists of brown marls and micaceous clays, marly conglomerates, Miocene brown sandstones, upper Pliocene limestones and Plio-Pleistocene red marls of brick-red silty clay. Recent alluvial deposits occur along the SE and NW cost and along numerous valleys, which traverse the peninsula. The Megali Kypsa settlement lies within the Quaternary alluvial deposits, closely surrounded by the red marls and brown sandstones. It is very likely that these formations provided the raw material used for the construction of the kilns as well as their products. Excavations in the area started in May 2006, and lasted until December 2007. The unearthed findings revealed an important settlement of a Late

157

Roman-Early Byzantine age, belonging most probably to an officer or magistrate. The complex, named “Megali Kypsa” hosted, apart from residential buildings and a Basilica, several ceramic kilns, which impressed by their size and state of preservation (Fig. 1b). Such important workshops are not very common within the excavated Greek antiquity. In her compilation of ancient Greek kilns, Hasaki (2002) and Hasaki and Palyvou (2006) refers to 459 examined firing structures, corresponding to at least 296 workshops. Among them, 14% have two kilns whereas workshops with three or more kilns represent only 10% of all sites. Though the above total number has certainly increased due to recent excavations, as the one studied here, it is very unlikely that these proportions changed dramatically. A total of 9 kilns were excavated and archaeologically studied in order to understand their construction and usage. Their stratigraphic relation suggests a possible, but not certain contemporary use. Their upper part – the dome – was not preserved mostly because of the friable clays and the “rebuilding” practice, which consisted in destroying and rebuilding it after every use. Therefore, only the lower parts and “hypocaustes” were investigated, providing useful information about their form, functioning, baked products and relation to the settlement. These kilns were of “updraft” style, constituted by two superimposed compartments, separated by the perforated floor or “eschara,” which allowed the upward heat flow. The lower part is the combustion chamber where the gases from the fuel are concentrated, while the upper part is the firing chamber, which is rarely preserved. The whole structure was built into a pit, initially excavated within the surrounding sediment mass, in order to ensure economy in energy and heat, and thermal isolation of the combustion chamber. The walls and floors were covered by clay coating, which was indurated after the repeated heatings. A complicated architectural structure within the kilns, with parallel walls, arch-shaped junctions and corridors was meant to guarantee the best possible support of the “eschara”, as well as the easy and isothermal transmission of heat. Firing temperatures reached 800 °C–950 °C after several hours of progressive heatings, starting from initial temperatures of 300 °C–500 °C at which organic inclusions burned and water evaporated, through 500 °C–600 °C at which ceramic products started being fired (Johnson et al., 1988) After the high temperature was stabilized, a

Fig. 1. (a) Map showing the location of Megali Kypsa. (b) General view of the settlement and (c)–(e) corresponding photos of the three studied kilns.

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progressive cooling ended the cycle. This procedure was typical in all Protobyzantine–Byzantine ceramic workshops in Greece where more than 60 were studied and dated between the 4th and 14th century AD (Raptis, 2012). Within the nine kilns investigated by the excavator, four are circular, three rectangular, whereas for the remaining two no clear indication for their shape could be seen. Our sampling has been conducted within the circular ones, which had diameters as follows: SAN6 d = 4 m, SAN10 d = 5 m and the previously studied SAN8 d = 3.2 m (Fig. 1c–e). The large size of the kilns and the examination of their content, such as big tiles, bricks or small clay bars, pyramid-shaped, known to be used as supports during functioning of kilns, suggest that at least some of them were used for the building material of the complex. Unfortunately, no pottery was found within them. Nevertheless, their size, number and position close to the sea, favor a broader artisanal production. The existence of numerous traces of ceramic kilns in other places nearby – Mikri Kypsa and Koutsoupia – supports a developed ceramic production within the broader area. It is reasonable to suggest that the geological conditions, together with the wind direction for the maintenance of fire, favored this activity and that the deriving clay was of high quality for construction purposes. It is suggested that this clay is also suitable for archaeomagnetic analysis as it will be further discussed. Our sampling started in June 2007 with kiln number 8 (SAN8) with 10 hand samples, which were subsequently treated and studied. All relevant information can be found in Aidona et al. (2010). Following the progress of the archaeological study, two other kilns were sampled in 2009 (SAN6 and SAN10), with 10 hand samples from each kiln while some tiles were retrieved from kiln SAN5 (Fig. 1). In spite of the important number of excavated structures, only these three guaranteed “in situ” conditions and good preservation for a reliable archaeomagnetic study. These results will be compared and combined with the ones from kiln SAN8 (Aidona et al., 2010). All samples (baked clays) were independently oriented with a magnetic and a sun compass and a bubble inclinometer was used for measuring the dip. In the laboratory the samples were set in blocks of plaster and cut into standard 2.5 × 2.2 cm cylinders. Between 5 and 15 sub-samples (specimens) were cut from each hand sample. In few cases, and in spite of the consolidation protocol followed, specimens were destroyed during treatment. Most of these specimens came from kiln SAN8. Finally TL dating was performed on several samples from the three kilns as well as on SAN5, which was not preserved enough for providing oriented samples, but could contribute to better constrain the dating of the site. 3. Luminescence dating Luminescence dating methods encompass a range of techniques, which are capable to determine the age of crystalline sedimentary materials. These techniques are based on a radiation-induced charge population within the sedimentary materials, and record the time since the last event, when the charge population was reset (Aitken, 1985). For volcanic, ceramic, fired, and baked clay materials, as in the case of kilns, the resetting event is either their accidental or intentional firing. Luminescence is the light emitted from minerals, such as quartz and feldspar, following an exposure to ionizing radiation. It arises due to the presence of defects in the mineral's crystal lattice. Ionizing radiation creates free electrons and holes in the lattice and a few of these get trapped in defects with opposite charges (McKeever, 1985). The residence time of charges in the defects can range from a few seconds to million years. The trapped charges can additionally be excited by an external thermal or optical stimulus, such as heating to 500 °C as well as day or laboratory light exposure of several seconds; giving thus rise to thermoluminescence, TL, or Optically Stimulated Luminescence, OSL, respectively. The freed charges then wander in the crystal lattice and some of these radiatively recombine with the opposite charges at another defect site

to release light. The intensity of the emitted light is proportional to the concentration of trapped charges/electrons and hence to the radiation dose. The latent luminescence signal increases till a saturation of trapped charges occurs. Dating using luminescence is made possible by the fact that in natural archaeological and geological environments, the decay of natural radio-nuclides, namely potassium and radioactive decay chains such as uranium, thorium along with cosmic radiation, provide a constant irradiation field (Wagner, 1998). Therefore, the minerals in the sediment or archaeological object are irradiated at a constant rate, and hence acquire latent luminescence. Towards the direction of age determination, two different physical quantities are required: the total accumulated dose during the past, termed as paleodose or equivalent dose (ED) in units of Gray (Gy) and the rate at which this energy-dose is accumulated, termed as dose rate (in units of Gy/a). The luminescence age equation is the ratio between the measured total absorbed dose (estimated as equivalent dose, ED by luminescence) and the dose-rate (DR) of ionizing radiation in the environment surrounding the dated material: age ¼

Equivalent Dose ED ¼ Dose Rate DR

4. Experimental methods 4.1. Archaeomagnetic method The natural remanent magnetisation (NRM) was measured using a Minispin spinner magnetometer (Molspin, Newcastle, UK). Alternating Field (AF) demagnetisation was performed by using a Molspin-MSA2 AF-tumbler demagnetiser (Molspin, Newcastle, UK) while for thermal demagnetisation a MMD80 oven was used. Isothermal remanent magnetisation (IRM) was imparted using an impulse magnetiser (ASC IM10-30) and a maximum field of 1.2 T. All the above experiments were performed in the Palaeomagnetism Laboratory of Thessaloniki University, School of Geology (Greece). The archaeointensities were calculated with the Triaxe protocol (Le Goff and Gallet, 2004) in the Palaeomagnetism Laboratory of Institut de Physique du Globe de Paris (St. Maur -France), with the decisive participation of Dr. Maxime LeGoff. The anisotropy of magnetic susceptibility was measured on a Kappa bridge KLY 4S (Geophysical Centre of the Royal Meteorological Institute, Dourbes, Belgium). High-temperature monitoring of magnetic susceptibility (thermomagnetic analysis) was performed with a Kappa bridge KLY 3 (Institut de Physique du Globe, Paris) in order to determine the Curie point of the magnetic minerals present in the material, as well as a possible alteration during heating. The experiments were carried out in air. Magnetic susceptibility changes were recorded continuously from room temperature up to 600 °C (heating curve) and back to room temperature (cooling curve). 4.2. Thermoluminescence method Treatment and preparation for all samples were undertaken in subdued red filtered light conditions. A 5 mm layer was removed from all clay sample surfaces to eliminate the light-subjected portions. Then each ceramic sample was crushed in an agate pestle and mortar. For the sample preparation the chemical procedure described by Vieillevigne et al. (2007) was applied. Fine grains between 4 and 11 μm were separated from coarse grains by sinking them into acetone solvent according to the ‘fine grain method’ (Zimmerman, 1971). For the equivalent dose estimation, the multiple aliquot, additive dose procedure (MAAD) in TL was applied; the procedure is described thoroughly by Aitken (1985, 1998) and Wagner (1998). All TL measurements were carried out at the Laboratory of Radiation Applications and

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Archaeological Dating, Athena -Research and Innovation Center in Xanthi-, Greece, using a Risø TL/OSL reader (model TL/OSL DA-15), equipped with a 90Sr/90Y beta particle source, delivering a nominal dose rate of 0.071 Gy/s. A 9635QA photomultiplier tube was used for light detection. The detection optics consist of a combination of a Pilkington HA-3 heat absorbing and a Corning 7–59 (320–440 nm) blue filter. All TL measurements were performed in a nitrogen atmosphere at a slow constant heating rate of 1 οC/s, in order to avoid a significant temperature lag, up to the maximum temperature of 500 οC. The additive doses applied were 7, 14 and 21 Gy. The dose rate is calculated based on the decay of naturally occurring radionuclides inside the clay matrix, i.e., 40K, 232Th and natural U, along with cosmic rays, which provide a constant source of low-level ionizing radiation. The latter two were measured using thick source alpha counting (Hossain et al., 2002), while 40K was estimated by applying X-ray fluorescence (XRF). Finally, in order to determine the gamma dose rate, two lithium fluoride chips (LiF:Mg,Ti) were implanted to the excavation area for 60 days. Dose-rate calculations were made using the conversion factors of Adamiec and Aitken (1998). 5. Archaeomagnetic results

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displayed in Fig. 3 show a very satisfactory reversibility indicating that no significant mineralogical alterations have occurred during heating up to 550–600 °C. The Curie temperatures vary from 500 °C to 580 °C, characteristic for the presence of magnetite or substituted magnetite. This is also confirmed by the results of thermal demagnetisation of the IRMs as shown in Aidona et al., 2010 and the NRMs (Fig. 5b). c. Thermal demagnetisation of the 3-axes composite IRM (Lowrie, 1990) was performed on samples from kiln SAN8 after imparting different fields on the 3 axes (0.1 T on x axis, 0.5 T on y axis and 2.5 T on Z axis). In all cases the soft magnetic fraction is dominant. No significant remanence is left after heating to 580 °C, independently of the different magnetizing fields (Aidona et al., 2010). d. Since the dominant magnetic carrier of the studied material is magnetite, we proceeded to the Lowrie–Fuller experiment on 16 representative samples from kilns SAN6 (10) and SAN10 (6). Specimens from kiln SAN8 were either broken due to their fragility or were already used in a previous study for the determination of the magnetic components through thermal demagnetisation of the 3-axis composite IRM (Aidona et al., 2010).

5.1. Mineral magnetism Results of the L-F experiment can be classified in 3 groups: The identification of the magnetic carriers and their degree of thermochemical stability during heating are critical in order to evaluate the material's suitability for obtaining reliable archaeomagnetic directions and intensities. The color of all samples was largely homogeneous, varying between reddish to brownish red; therefore we selected specimens on the basis of their distribution within the kilns and material condition-friability, accessibility etc. In general, the samples were not particularly anisotropic, with the degree of anisotropy (p′) ranging from 1% to 4% which is very low. Insignificant anisotropy values are to be expected for such kind of material (baked clays) as referred in Hus et al. (2002) among others. a. Isothermal remanent magnetisation was imparted in representative samples from all kilns. For the majority of samples, saturation seems to occur in low fields (up to 400mT) indicating the presence of low coercivity magnetic minerals such as magnetite phases. Only in few cases the saturation is not reached up to 1.2 T, pointing to a harder component possibly present in these samples (Fig. 2). Monitoring of susceptibility variations with temperature during the thermal demagnetisations did not reveal significant changes. As deduced from the above experiments, our samples did not suffer significant alteration during heating. b. The variation of magnetic susceptibility with temperature was monitored in all samples from the 3 kilns. Thermomagnetic curves

1. Samples with mixture of MD and SD magnetite (Fig. 4a) 2. Samples with SD magnetite (Fig. 4b). 3. Samples with MD magnetite (Fig. 4c). The majority of the samples belong to groups 1 (N = 4) and 2 (N = 7) therefore 11 out of 16 samples contain SD grains. 5.2. Directional results Measurements of the NRM directions have been performed on all specimens of the two kilns (San6, 10). The results show a satisfactory grouping, therefore samples were sufficiently burnt “in situ” with only few exceptions referring to samples mainly located at some distance of the estimated firing center. Specimens from both kilns have been subjected to AF and TH demagnetisation. Both demagnetisation techniques reveal the presence of one stable component while a secondary viscous component, when visible, was easy to remove at low fields (max 10mT) or temperatures (max 100 °C) (Fig. 5a, b). The majority of the specimens were fully demagnetised at 100mT or 580 °C indicating low coercivity minerals as main NRM carriers. The direction of the Characteristic Remanent Magnetisation (ChRM) was calculated using the principal component analysis (Kirschwink, 1980) including the origin of the coordinate system by Remasoft software (Chadima and Hrouda, 2006). The ChRM was determined using at least 5 demagnetisation steps while the obtained directions yielded moderately small maximum angular deviation (MAD) values b 4°. The mean values were calculated at the specimen level. Stereographic projections of the calculated mean values are plotted in Fig. 6 and presented in Table 1. 5.3. Archaeointensity experiments following the “Triaxe” protocol

Fig. 2. Representative IRM acquisition curves from the studied kilns.

In the archaeointensity experiments material from SAN8, SAN6, and SAN10, was used for the determination of the archaeointensities. The Triaxe protocol is designed to perform automated high temperature magnetisation measurements on small cylindrical specimens of b1 cm3 in volume. It involves several continuous zero-field heating and cooling cycles up to a maximum temperature of 580 °C with a rate of 25 °C/min and one in-field cooling cycle (Le Goff and Gallet, 2004). Magnetisation was monitored through all cycles with a threeaxis vibrating sample magnetometer within a three-axis Helmholtz

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Fig. 3. Variation of magnetic susceptibility with temperature (after holder correction) for representative samples from the three kilns.

coil system, covered by a μ-metal shield. It has to be noted that anisotropy of TRM is automatically corrected by adjusting the field orientation in order to obtain remanent magnetisation in the NRM direction. The archaeointensity is defined as the mean of parameter R′(T) over the used temperature range. As described in Gallet and LeGoff (2006), the quality criteria applied in order to discriminate successful from unsuccessful experiments rely on the presence of a unidirectional NRM, a smooth shape of the R′(T) curve, a slope of R′(T) that is lower than 15% and the fact that more than 50% of the NRM is involved in the calculation of archaeointensity. Results from SAN8 were already presented by Aidona et al. (2010). These came from 4 samples and in the present study a fifth one was added for a better precision. Samples from kilns SAN6 and SAN10 were first selected on the basis of reversibility of thermomagnetic curves. From SAN6, 8 samples have been analyzed. Two of them, SAN6-04, showing a second magnetisation component, and SAN6-08, too weak (b40 × 10− 8 Am2), were eliminated. The 6 others presented a single directional component, and were suitable for good intensity results. The same applies to all 5 analyzed samples from SAN10. Characteristic R′(T) curves from the studied samples together with the obtained values are presented in Fig. 7. The mean values are reported in Table 1 with the number of individual determinations of intensity (NF in Table 1).

6. Thermoluminescence analysis 6.1. Equivalent dose estimation Fig. 8 presents characteristic glow curves of the additive-dose procedure for sample SAN6–5. Each glow curve is the mean value of three independently measured glow curves. The inset of Fig. 8 presents the four different glow curves of the natural TL (NTL) signal, providing strong evidence towards the excellent mass repeatability after the procedure of acetone solving. Moreover, a background signal measurement, which was subtracted from each glow curve, is also presented in the inset of Fig. 8; it is the curve whıch does not provide peaks. Equivalent doses were calculated with 1σ error values; a typical plot of equivalent dose (ED) against glow curve temperature is presented in Fig. 9. Errors derived mainly from the uncertainties in curve fitting, are ± 1σ and were calculated by standard error propagation analysis (Knoll, 1999). In all cases, ED plateaus are wide enough, over 70 °C wide. The equivalent doses were obtained as the mean values of the best plateaus for each sample. Only linear fittings were performed to the dose response curves. This linearity was strongly established in the inset of Fig. 9, where a representative example of an additive buildup curve is also presented as filled squares for the temperature corresponding to the temperature in the middle of the plateau range, along with the corresponding linear fit. This inset figure strongly supports

Fig. 4. Lowrie–Fuller test with the three representative cases (see text for details).

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Fig. 5. (a) and (b) Representative Zijderveld diagrams and demagnetisation curves during the AF (a) and thermal (b) demagnetisation. The presence of a small viscous component and a univectorial TRM is displayed.

the linearity monitored for the case of the dose response. In the same inset, filled diamonds present the corresponding second glow TL dose response curve after applying low doses, indicating the absence of supra-linearity in the low-dose region (Fleming, 1979). A summary of the TL dating data is provided within Table 2.

Due to the fact that the samples contain feldspars, the possibility of an anomalous fading correction was also taken under consideration. For the present study the procedure previously applied by Tema et al. (2013a, 2014) was also adopted; however in the framework of the present study the dose applied was similar to the equivalent dose of

Fig. 6. Stereographic projection of the mean direction of the characteristic remanence magnetization (ChRM) for the studied kilns. Black points represent the ChRM direction of the specimens while the purple point represents the mean calculated direction for the kiln.

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Table 1 Summary of the new archaeomagnetic results. Kiln = name of the studied kiln; Lat/Long = site latitude/longitude; N = number of specimens; D = declination; I = inclination; α95 = 95% semi-angle of confidence; k = Fisher's precision parameter; NF = number of successful specimens to the total number of studied specimens during the archaeointensity experiment; F = intensity. Kiln

Lat/Long (°)

N

D (°)

I (°)

a95 (°)

k

NF

F (μΤ)

Sani 6 Sani 10 Sani 8

40.07/23.3 40.07/23.3 40.07/23.3

31 21 –

357.8 358.2 –

55.9 52.8 –

3.0 3.1 –

76 106 –

6/8 5/5 5/5

59.5 ± 2.5 61.2 ± 1.1 63.06 ± 3.4

each kiln while the storage time was three months. Eventually, negligible anomalous fading was detected, less than 1%, a value, which does not require any correction. This absence of anomalous fading is strongly supported by the glow curve shapes in Fig. 8, as these glow curves are dominated by typical quartz TL peaks.

6.2. Dose rate estimation The dose rate is calculated based on the decay of naturally occurring radionuclides inside the clay matrix, i.e., 232Th, 40K, and natural U. Dose rate is defined as the annual irradiation dose and consists of two independent parameters, the internal and the external dose rate. The internal dose rate is due to the radioactive elements that any ceramic material contains. Those that gather greater attention are 40K, 235Useries, 238U-series, and 232Th-series and to some extent Rb (Aitken, 1985). The external dose rate mainly consists of external γ-dose rate of the sediment and the cosmic dose rate. About one gram of untreated clay from each sample was employed to perform thick source alpha counting with a ZnS detector. The measurements were performed both in the integral and in the pair counting mode, for the discrimination between Th and U (Hossain et al., 2002). It was assumed that U and 232Th concentrations were uniformly distributed all over the sample. Measurements with duration longer than 5 days each were carried

Fig. 7. Successful archaeointensity determinations from the three kilns applying the Triaxe protocol. The archaeointensity is defined as the mean of parameter R′(T) over the used temperature range. The percentages following the letter “K” in the legends are for the part of NRM involved in the calculation of R′, and those following “s” are for the slope.

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SAN 6-5

1000

NTL (a.u.)

30000

NTL+21 Gy

25000

100

TL

20000 10

15000

0

NTL+14 Gy

100

200

300

400

Temperature (oC)

10000

NTL+7 Gy 5000

163

(±0.064) ka before present was yielded. For all values, the first parenthesis indicates the standard deviation on the mean value; low values indicate the repeatability of the individual ages yielded from each sample of the same kiln. The second parenthesis indicates the error estimated according to each individual error value according to standard error propagation analysis. Similarly, for the case of kiln SAN10, a mean age value of 1.453 (±0.182) (±0.053) ka BP was adopted. Finally for kiln SAN6 a mean age of 1.504 (±0.039) (±0.084) ka before present was estimated. Moreover, for kiln SAN5, which was only dated by TL, a mean value of 1.664 (± 0.094) (± 0.085) ka BP was yielded. The four kilns were thus dated back to 350 ± 85, 360 ± 64, 509 ± 84 and 560 ± 53 AD for kilns SAN5, SAN8, SAN6 and SAN10 respectively.

NTL 0

7. Discussion 0

100

200

300

400

500

Temperature (oC)

7.1. Quality of the raw material

Fig. 8. Natural (NTL) and natural-plus-beta dose glow curves for the sample SAN6-5. The additive doses delivered were highlighted as arithmetics inside the Fig. Reheats have been subtracted. Each glow curve plotted is the average of three individually measured glow curves. Inset presents 4 NTL curves, indicating the mass-repeatability along with a background noise measurement (signal without peaks).

out, according to the methodology proposed by Aitken (1985). The measurements were calculated at the 7286 Low Level Alpha Counter, Littlemore Sci. Eng Co Oxford with a photomultiplier (PM) tube type EMI 6097B, calibrated in standards following devised conversion factors as well as relevant computations. The sample gave sealed over unsealed ratio of 1.029, which is considered as to represent insignificant Rn escape under laboratory conditions (Aitken, 1985). The k-factor, i.e. the efficiency of the alpha particles compared to beta particles was adopted to be 0.1 (Polymeris et al., 2011). Table 2 presents also the outline of the dose rate assessment procedure. Finally, the use of the two lithium fluoride chips (LiF:Mg,Ti) verified the fact that the external gamma dose rate results derived mainly from natural radioactivity in the kiln and the cosmic rays dose rate. 6.3. TL ages Four different kilns were dated in the framework of the present study. For the case of kiln SAN8, a mean value of 1.653 (± 0.049)

5.0

SAN 6-5

10000

2.5

8000

TL (a.u.)

ED (Gy)

12000

6000 4000 2000 0 -5

ED

0.0 200

0

5

10

15

20

25

Additive Dose (Gy)

300

400

Temperature (oC) Fig. 9. Equivalent dose versus temperature for the sample SAN6-5. Solid line indicates the best ED plateau. Inset: A representative NTL+β (filled squares) and regenerated β (filled diamonds) plot for the temperature of 300 °C. The arrow shows the equivalent dose.

In general, clays used for the construction of ceramic workshops are not particularly selected, thus they are very similar to the soils surrounding each site. In the present case the important sedimentary outcrops of the broader area provided the raw material therefore their magnetic content should be suitable to ensure reliable measurements (Jordanova et al., 2001; Kostadinova-Avramova and Kovacheva, 2013). This was certified through the outcome of a palaeomagnetic study previously conducted in the area. During a field campaign in summer 1996, the Miocene/Pliocene sediments of the broader area were sampled and measured. Their magnetisation was quite weak (magnitude orders 10−2 to 10−5 A/m) and susceptibility low (10 to 450 × 10− 6 SI, with a majority between 50 and 150 × 10−6 SI). This did not prevent reliable results to be obtained: stable ChRM components, with the expected eastwards directions for the area, and recording at least one reversal (Haubold et al., 1997; Mauritsch, Scholger, and Kondopoulou, unpublished data). Factors which can affect the suitability of baked clays for archaeomagnetic studies, apart the initial composition of the unbaked material, are the degree of heating in antiquity and the burial conditions (Jordanova et al., 2003). Since the studied kilns produced both building material and ceramic crafts, the temperatures reached were probably sufficiently high for imparting a TRM to the clay samples. In a study on 14 kilns conducted on four Hellenistic-Early Roman ceramic workshops in Greece a broad range of firing temperatures was determined through detailed mineralogical analysis on at least 3 samples per kiln. The derived temperatures, apart few exceptions, lie in the range of 700 °C–800 °C (Rathossi et al., 2012; Kondopoulou et al., 2014). A similar study, conducted on building material samples collected from an early Hellenistic kiln excavated in Kato Achaia (NW Peloponnese, Southern Greece), estimated firing temperatures between 800 and 1050 °C (Rathossi et al., 2012). Moreover, from the same geographical region, the archaeometric research in a large number of lamp sherds derived from two roman workshops (1st to 3rd AD) unearthed in Patras (at 27 km distance from Kato Achaia), also determined the use of high firing temperatures of about 800–1050 °C during the kiln operation (Rathossi et al., 2004; Rathossi, 2005). The raw clay paste used for the production of kiln materials and lamp sherds proves to be similar with the surrounding geological environment. Such high firing temperatures for kilns are not always stable during firing. For instance, in a Roman pottery kiln in Belgium ancient baking temperatures were estimated at 800–950 °C based on a mathematical model but they did not exceed 600 °C at a distance of 65–80 mm from the combustion chamber (Spassov and Hus, 2006). Nevertheless, the ceramic technology in Greece, at that period, was elaborated enough to ensure high firing temperatures. The kilns technology in the Protobyzantine period was an evolution of the previous, Hellenistic-Early Roman one (Petridis, 2013) and all the above measurements covered structures and productions from a broad

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Table 2 Summary of the TL dating results, including ED = equivalent dose values, U = uranium, Th = thorium and K = potassium concentrations, DR = dose rate and ages. Numerics inside parenthesis indicate the 1σ errors. NAME

ED (Gy)

U (ppm)

Th (ppm)

K (%)

DR (Gy/ka)

AGE (Ka BP)

AGE (AD)

SAN8-2 SAN8-3 SAN8-4 SAN8-5 SAN6-1 SAN6-5 SAN10-3 SAN10-7 SAN10-6 SAN10-9 SAN5C SAN5D

6.06 (0.23) 5.79 (0.25) 5.39 (0.31) 5.58 (0.39) 4.82 (0.32) 5.32 (0.32) 4.96 (0.29) 8.19 (0.48) 6.24 (0.35) 6.03 (0.34) 7.15 (0.46) 6.58 (0.33)

6.39 (0.10) 5.81 (0.08) 5.03 (0.13) 5.83 (0.12) 5.35 (0.11) 6.04 (0.13) 7.14 (0.14) 7.24 (0.11) 5.45 (0.13) 5.06 (0.13) 7.30 (0.11) 7.61 (0.12)

4.81 (0.18) 5.76 (0.17) 5.78 (0.13) 5.91 (0.11) 7.13 (0.15) 8.05 (0.18) 5.19 (0.12) 9.08 (0.15) 8.48 (0.11) 8.17 (0.15) 12.63 (0.13) 13.13 (0.11)

1.45 (0.02) 1.51 (0.02) 1.54 (0.02) 1.53 (0.03) 1.13 (0.03) 1.36 (0.02) 1.39 (0.02) 2.71 (0.03) 2.51 (0.04) 2.29 (0.04) 1.12 (0.05) 0.95 (0.03)

3.52 (0.12) 3.48 (0.12) 3.31 (0.14) 3.49 (0.15) 3.15 (0.14) 3.61 (0.13) 3.70 (0.13) 5.14 (0.14) 4.42 (0.13) 4.11 (0.12) 4.13 (0.15) 4.12 (0.12)

1.724 (0.098) 1.664 (0.099) 1.626 (0.131) 1.599 (0.144) 1.532 (0.132) 1.475 (0.111) 1.340 (0.107) 1.594 (0.112) 1.412 (0.101) 1.469 (0.109) 1.730 (0.137) 1.597 (0.105)

289 349 387 414 481 538 673 419 601 364 283 416

geological context. Thus, it is reasonable to consider these firing temperatures as valid also for the kilns presented here. Nevertheless firing conditions highly depend not only on samples position within the kiln but also on specimens' position within the

Fig. 10. Comparison of the new data with the Greek secular variation curves (thick solid line) accompanied by the error bars (dashed curves).

Fig. 11. Comparison of the new data with the predictions of the global ARCH3K.1 (purple line) and the regional SCHA.DIF.3K (black line) geomagnetic field models. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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Fig. 12. Archaeomagnetic dating of SAN6, SAN8 and SAN10 using the Matlab tool for archaeomagnetic dating by Pavón-Carrasco et al., 2011. Combined age estimations are shown in the lower right part of the graph for each kiln.

same fragment. This feature was thoroughly examined through several studies conducted on bricks (e.g., Aidona et al., 2008; Catanzariti et al., 2008). More recently, Morales et al. (2011) confirmed vertical and radial temperature gradients – between 100° and 300 °C – within a test kiln for ceramics. 7.2. Evaluation of results The demagnetisation of the studied material revealed a reliable record of the directions of the geomagnetic field. However values of α95 are moderately high-3.0 for SAN6 and 3.1for SAN10- and could possibly reflect some orientation error in the field and/or the laboratory preparation. Nevertheless, such values were obtained even in cases where samples were extracted by a portable drill (Gómez-Paccard et al., 2013) and a possible disturbance of the kiln during excavation cannot be ruled out. It is clear that simple orientation errors, if any, could not be the single factor for dispersion of results. Concerning the intensity values the majority of the specimens studied provided successful results following the Triaxe protocol and quality criteria. The two new intensity values calculated from kilns SAN6 and SAN 10 as well as the recalculation of SAN 8 which is practically identical with the previously published one, are presented in Table 1. After evaluating the TL and archaeological ages we adopt as possible dates for the kilns' last use the following: SAN5, SAN8: 350 ± 85 AD and 360 ± 64 AD respectively SAN6, SAN10: 509 ± 84 AD and 560 ± 53 AD respectively.

These values are used in order to plot our results accordingly. We draw the attention to the following: kiln SAN8 was included in the recently compiled Greek directional curves, by using the mean archaeological age available at that time (300 AD). The new TL dating and updated archaeological information shift this age at least 60 years later. In order to evaluate the obtained directions and intensities a comparison with existing SVCs and GMF models is attempted. In Fig. 10 our results are plotted with the available SVC curves from Greece (De Marco et al., 2008 for intensity; De Marco et al., 2014 for directions). All data are reduced to the latitude of Athens (37.97N/23.72E) following the method proposed by Noel and Batt (1990). Both declinations and inclinations are close to the Greek directional curves (De Marco et al., 2014), constraining better a time span where results are fewer. Concerning the intensity results, two of the new values – kilns SAN6 and SAN10 – lie within the error bars of the SVC while the third one – kiln SAN8 – is in the close vicinity. It has to be noted that due to data dispersion and limited number for this period, the intensity curve is relatively ill-defined. In Fig. 11, we have plotted our new data, accordingly relocated, with two GMF models: a regional archaeomagnetic SCHA.DIF.3K proposed by Pavón-Carrasco et al. (2009) and the global ARCH.3K.1 proposed by Korte et al. (2009). Declination values are very consistent with both models while for inclination values a slight shift for kiln SAN10 is observed, within the respective error bars. The intensity values for kilns SAN6 and SAN10 lie within the two models' curves, while SAN8 is within the respective upper error bars

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of the models. As a whole, the new results converge to a very satisfactory extent with the two models. 7.3. Archaeomagnetic dating An attempt to date the 3 kilns of the site archaeomagnetically has been performed. At a first step local and regional curves (as the Greek and Balkan ones, De Marco et al., 2008, 2014; Tema and Kondopoulou, 2011 respectively) were used. Next, using the Matlab tool for archaeomagnetic dating by PavónCarrasco et al. (2011) based on a regional model (SCHA.DIF.3K), possible ages were tested. After the evaluation of the dating results the latter seems to give the better estimation. Therefore, it was chosen for the archaeomagnetic dating of the kilns. The full vector of the geomagnetic field was used and the possible dating periods were calculated by combining separately the probability functions for declination, inclination and intensity respectively. All probability density functions were calculated at 95% confidence level and the results are shown in Fig. 12. In the cases of SAN6 and SAN10 two possible intervals are observed. The first one, 79BC–205 AD for SAN6 and 24–232 AD for SAN10 can be discarded following the archaeological limitations. Several coins of Emperor Arcadios (395–408 AD) were unearthed, thus the beginning of the kilns' use can be placed in Late 3rd to Early 4th century AD. The end of this activity will be dated through the results of our study and is not necessarily associated to the end of the complex inhabitance, which could extend as far as late 8th century AD. In fact, the Basilica dating to the 8th century AD and one coin of Emperor Constantin 5th (741–775 AD) suggest a possible upper limit of the site's inhabitance. The second time span, 368–510 AD for SAN6, converges to a satisfactory overlap with the TL one (509 ± 84 AD) but also with the archaeological information. The period 259–439 AD derived from the archaeomagnetic dating for SAN10 is not compatible with the one suggested by TL (560 ± 53 AD). This discrepancy is probably related to the limited possibilities of the archaeomagnetic dating in the present case as explained below. For the Kiln SAN8 only one interval was estimated from 96–427 AD (Fig. 12), which overlaps with the TL period of 350 AD. However, the period until 350 AD at least has to be excluded by archaeological evidence since the settlement started at the end of the 4th century. We notice that inclination is the decisive factor for the dating since it is rapidly varying within the examined timespan while declination is practically constant and intensity's variation is also very smooth. Such constant declinations were already observed by De Marco et al. (2014) for this period, and also in Central and Western Europe for the period 500BC–500 AD (Márton, 2010). A recent study on Italian archaeointensities supports little or no variations for the period 200BC to 400 AD, around a mean value of 63 μΤ (Tema et al., 2013b). Our site lies very close to the 900 km radius around Viterbo, used in Tema et al. (2013b), and a tentative comparison (after relocation to Viterbo) yields the following values: SAN6 = 61.1 ± 2.5 μΤ, SAN8 = 64.7 ± 3.4 μΤ, SAN10 = 62.8 ± 1.1 μΤ with a mean of 62.9 μΤ ± 1.8, in full agreement with the Italian values. Therefore the archaeomagnetic dating depends mainly on inclinations, which could explain the fairly confined results of the archaeomagnetic dating in some cases. Consequently, a possible nonsynchroneity of the kilns' last use can be only supported by TL and archaeological information. At least one kiln – SAN5 – was used for the building material's production as deduced from the findings-tiles — thus belongs to the early period of the complex inhabitance. 8. Conclusions The big, archaeologically well-studied, Protobyzantine settlement of Megali Kypsa (North Greece) including an important ceramic workshop, provided material for an archaeomagnetic study accompanied by several TL dating results. Three kilns constructed mostly from

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baked clays of local origin were sampled. The clays are well-baked and proved to be suitable for the archaeomagnetic study, and a detailed rock magnetic analysis together with a complete demagnetisation procedure, including AF and thermal treatment, provided two new directions with satisfactory precision. The Triaxe protocol provided intensities with a mean of 61.2 μΤ ± 1.8. Following the TL datings and archaeological constrains, a possible chronological order in the kilns last use is suggested. Due to almost constant declinations and small variations of intensities within the examined period, this approach is mainly supported by inclination values. This outcome contributes considerably to the archaeological research for the Protobyzantine period. Despite the occurrence of numerous excavated sites, this period (3rd to 7th AD) lacks reliable archaeological constrains due to the type of findings. In fact and apart from specific products like amphorae, common pottery is difficult to characterize since the local ceramic productions were restrained and typology was not very elaborated (Petridis, 2007, 2013). Therefore such new input on chronologies is very welcome. The new results provide three new full vector points for the completion and improvement of the Greek SVCs for this period. Several more data are still needed and our study on structures of slightly younger age (5th to 6th AD) in the broader area is in progress (Aidona et al., 2013).

Acknowledgments The studied site has been indicated to us by Dr. I. Papaggelos, now Honorary Ephore of the 10th Ephorate of Byzantine Antiquities — Thessaloniki, which helped us in several ways. During the sampling we were assisted by A. Kougioumtzidis. Several measurements of magnetic mineralogy have been performed at the Paleomagnetism Laboratory of IRM (Dourbes-Belgium) with the assistance of Dr. S. Spassov who has also provided an extensive review of our manuscript together with a second, anonymous reviewer. They are all warmly thanked. Moreover, we acknowledge Dr. Nestor C. Tsirliganis for providing access to the TL/OSL infrastructures at the Laboratory of Radiation Applications and Archaeological Dating, Athena ‐ Research and Innovation Center in Xanthi, Greece. Last but not least, we are indebted to Dr. M. LeGoff (IPGP-St. Maur, France) who kindly performed and interpreted the Triaxe measurements, with the first author, in St. Maur (France).

References Adamiec, G., Aitken, M., 1998. Dose–rate conversion factors: update. Ancient TL 16, 37–49. Aidona, E., Kondopoulou, D., 2012. First archaeomagnetic results and dating of neolithic structures in Northern Greece. Stud. Geophys. Geod. 56, 827–844. Aidona, E., Scholger, R., Mauritsch, H.J., Perraki, M., 2008. Remanence acquisition in a Roman-style gold furnace. Phys. Chem. Earth 33, 438–448. Aidona, E., Kondopoulou, D., Alexandrou, M., Ioannidis, N., 2010. Archaeomagnetic studies in kilns from Northern Greece. Bull. Geol. Soc. Greece XLIII (4), 1888–1897. Aidona, E., Polymeris, G., Kondopoulou, D., Ioannidis, N., Macridis, P., 2013. Archaeomagnetic And Thermoluminescence Dating Of Historical Kilns From N. Greece. IAGA, Mexico. Aitken, M.J., 1985. Thermoluminescence Dating. Oxford Academic Press. Aitken, M.J., 1998. An Introduction To Optical Dating. Oxford University Press. Bornovas, J. and Rondogianni-Tsiambaou, TH., 1983. Geological map of Greece, 1:500.000, second edit., Institute for Geological and Subsurface Research, Athens. Catanzariti, G., McIntosh, G., Gόmez-Paccard, M., Ruiz-Martínez, V.C., Osete, M.L., Chauvin, A., The, A.A.R.C.H., Team, Scientific, 2008. Quality control of archaeomagnetic determination using a modern kiln with a complex NRM. Phys. Chem. Earth 33, 427–437. Chadima, M., Hrouda, F., 2006. Remasoft 3.0 — a user-friendly paleomagnetic data browser and analyzer. Trav. Géophys. XXVII, 20–21. De Marco, E., Spatharas, V., Gomez-Paccar, M., Chauvin, A. And, Kondopoulou, D., 2008. New archaeointensity results from archaeological sites and variation of the geomagnetic field intensity for the last 7 millennia in Greece. Phys. Chem. Earth 33, 578–595. De Marco, E., Tema, E., Lanos, Ph., Kondopoulou, D., 2014. An updated catalogue of Greek archaeomagnetic data for the last 4500 years and a directional secular variation curve. Stud. Geophys. Geod. 58, 127–147.

168

D. Kondopoulou et al. / Journal of Archaeological Science: Reports 2 (2015) 156–168

Donadini, F., Korte, M., Constable, C.G., 2009. Geomagnetic field for 0–3 ka: new data sets for global modelling. Geochem. Geophys. Geosyst. 10. http://dx.doi.org/10.1029/ 2008GC002295 Q06007. Fanjat, G., Aidona, E., Kondopoulou, D., Camps, P., Rathossi, C., Poidras, T., 2013. Archaeointensities in Greece during the Neolithic period: new insights into material selection and secular variation curve. Phys. Earth Planet. Inter. 215, 29–42. Fleming, S., 1979. Thermoluminescence Techniques In Archaeology. Clarendon Press. Gallet, Y., LeGoff, M., 2006. High-temperature archeointensity measurements from Mesopotamia. Earth Planet. Sci. Lett. 241, 159–173. Gallet, Y., Genevey, A., Le Goff, M., 2002. Three millennia of directional variation of the Earth's magnetic field in Western Europe as revealed by archaeological artefacts. Phys. Earth Planet. Inter. 131, 81–89. Genevey, A., Gallet, Y., Constable, C., Korte, M., Hulot, G., 2008. ArcheoInt: an upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to recovery of the past dipole moment. Geochem. Geophys. Geosyst. 9, Q04038. http://dx.doi.org/10.1029/2007GC001881. Genevey, A., Gallet, Y., Thebault, E., Jesset, S., Le Goff, M., 2013. Geomagnetic field intensity variations in Western Europe over the past 1100 years. Geochem. Geophys. Geosyst. 14, 2858–2872. Gómez-Paccard, M., Lanos, Ph., Chauvin, A., McInstosh, G., Osete, M.L., Catanzariti, G., Ruiz-Martınez, V.C., Núnez, J.I., 2006. First archaeomagnetic secular variation curve for the Iberian Peninsula: comparison with other data from Western Europe and with global geomagnetic field models. Geochem. Geophys. Geosyst. 7, Q12001. http://dx.doi.org/10.1029/2006GC001476. Gómez-Paccard, M., Chauvin, A., Lanos, P., Thiriot, J., 2008. New archaeointensity data from Spain and the geomagnetic dipole moment in western Europe over the past 2000 years. J. Geophys. Res. 113, B09103. Gómez-Paccard, M., Chauvin, A., Lanos, Ph., Dufresne, Ph., Kovacheva, M., Hill, M.J., Beamud, E., Blain, S., Bouvier, A., Guibert, P., Team, Archaeological Working, 2012. Improving our knowledge of rapid geomagnetic field intensity changes observed in Europe between 200 and 1400 AD. Earth Planet. Sci. Lett. 355–356, 131–143. Gómez-Paccard, M., Beamud, E., McIntosh, G., Larrasoana, J.C., 2013. New archaeomagnetic data recovered from the study of three Roman kilns from North-East Spain: a contribution to the Iberian palaeosecular variation curve. Archaeometry 55, 159–177. Hasaki, E., 2002. Ceramic Kilns In Ancient Greece: Technology And Organization Of Ceramic Workshops. University of Cincinnati (Ph.D. thesis). Hasaki, E., Palyvou, C., 2006. The ancient Greek ceramic kilns and their contribution to the technology and organization of the potters' workshops. In: Tasios, P. (Ed.), Proceedings Of The 2nd International Conference On Ancient Greek Technology, Athens, pp. 221–227. Haubold, H., Scholger, R., Kondopoulou, D., Mauritsch, H.J., 1997. New palaeomagnetic results from the Aegean extensional province. Geol. Mijnb. 76, 45–55. Hossain, S.M., De Corte, F., Vandenberghe, D., Van den haute, P., 2002. A comparison of methods for the annual radiation dose determination in the luminescence dating of loess sediment. Nucl. Inst. Methods Phys. Res. A 490, 598–613. Hus, J., Ech-Chakrouni, S., Jordanova, D., 2002. Origin of magnetic fabric in bricks: its implications in archaeomagnetism. Phys. Chem. Earth 1319–1331. Johnson, J.S., Clark, J., Miller-Antonio, S., Robbins, D., Schiffer, M.B., Skibo, J.M., 1988. Effects of firing temperature on the fate of naturally occurring organic matter in clays. J. Archaeol. Sci. 15, 403–414. Jordanova, N., Petrovsky, E., Kovacheva, M., Jordanova, D., 2001. Factors determining magnetic enhancement of burnt clay from archaeological sites. J. Archaeol. Sci. 1137–1148. Jordanova, N., Kovacheva, M., Hedley, I., Kostadinova, M., 2003. On the suitability of baked clay for archaeomagnetic studies as deduced from detailed rock-magnetic studies. Geophys. J. Int. 153, 146–158. Kirschwink, J.K., 1980. The least-square line and plane and the analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc. 62, 699–718. Knoll, F.G., 1999. Radiation Detection And Measurements. third ed. J. Wiley & Sons, Inc. Kockel, F., Mollat, H., and Walther, H.W., 1977. Erlauterungen zur Geologischen Karte der Chalkidiki und Angrenzender Gebiete 1:100.000 (Nord-Griechenland), Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover. Kondopoulou, D., Zananiri, I., Rathossi, Ch., De Marco, E., Spatharas, V., Hasaki, E., 2014. An Archaeometric And Archaeological Approach To Hellenistic — Early Roman Ceramic Workshops In Greece: Contribution To Dating. Joint Issue Of Tree-Ring Research And Radiocarbon Dating 56 (4), 27–38. Korte, M., Genevey, A., Constable, C., Frank, U., Schnepp, E., 2005. Continuous geomagnetic field models for the past 7 millennia: 1. A new global data compilation. Geochem. Geophys. Geosyst. 6, Q02H15. http://dx.doi.org/10.1029/2004GC000800. Korte, M., Donadini, F., Constable, C.G., 2009. Geomagnetic field for 0–3 ka: 2. A new series of time-varying global models. Geochem. Geophys. Geosyst. 10, Q06008. http://dx. doi.org/10.1029/2008GC002297. Kostadinova-Avramova, M., Kovacheva, M., 2013. The magnetic properties of baked clays and their implications for past geomagnetic field intensity determinations. Geophys. J. Int. 95, 1534–1550. Kovacheva, M., Jordanova, N., Karloukovski, V., 1998. Geomagnetic field variations as determined from Bulgarian archaeomagnetic data. Part II. The last 8000 years. Surv. Geophys. 19 (5), 431–460. Kovacheva, M., Boyadziev, Y., Kostadinova–Avramova, M., Jordanova, N., Donadini, F., 2009. Updated Archaeomagnetic Data Set Of The Past 8 Millennia Form The Sofia Laboratory, Bulgaria. Geochem. Geophys. Geosyst. 10 (5), Q05002. http://dx.doi.org/ 10.1029/2008GC002347.

Le Goff, M., Gallet, Y., 2004. A new three-axis vibrating sample magnetometer for continuous high-temperature magnetization measurements: applications to paleo- and archeointensity determinations. Earth Planet. Sci. Lett. 229, 31–43. Lowrie, W., 1990. Identification of ferromagnetic minerals in a rock by coercivity and unblocking temperature properties. Geophys. Res. Lett. 17, 159–162. Márton, P., 2010. Two thousand years of geomagnetic field direction over central Europe revealed by indirect measurements. Geophys. J. Int. 181, 261–268. Márton, P., Ferencz, E., 2006. Hierarchical versus stratification statistical analysis of archaeomagnetic directions: the secular variation curve for Hungary. Geophys. J. Int. 164, 484–489. http://dx.doi.org/10.1111/j.1365-246X.2006.02873.x. McKeever, S.W.S., 1985. Thermoluminescence Of Solids. Cambridge University Press. Morales, J., Goguitchaichvili, A., Aguilar-Reyes, B., Pineda-Duran, M., Camps, P., Carvallo, C., Calvo-Rathert, M., 2011. Are ceramics and bricks reliable absolute geomagnetic intensity carriers? Phys. Earth Planet. Inter. 187 (3–4), 310–321. Noel, M., Batt, C.M., 1990. A method for correcting geographically separated remanence directions for the purpose of archaeomagnetic dating. Geophys. J. Int. 102, 753–756. Pavón-Carrasco, F.J., Osete, M.L., Torta, J.M., Gaya-Piqué, L.R., 2009. A regional archaeomagnetic model for Europe for the last 3000 years, SCHA.DIF.3K: applications to archaeomagnetic dating. Geochem. Geophys. Geosyst. 10 (3), Q03013. http://dx. doi.org/10.1029/2008GC002244. Pavón-Carrasco, F.J., Osete, M.L., Torta, J., 2010. Regional modeling of the geomagnetic field in Europe from 6000 BC to 1000 BC. Geochem. Geophys. Geosyst. 11, Q11008. http://dx.doi.org/10.1029/2010GC003197. Pavón-Carrasco, F.J., Rodriguez-Gonzalez, J., Osete, M.L., Torta, J., 2011. A Matlab tool for archaeomagnetic dating. J. Archaeol. Sci. 38 (2), 408–419. Petridis, P., 2007. Relations between pottery workshops in the Greek mainland during the Early Byzantine period. In Bohlendorf-Arslan-Uysal-Witte-Orrpp. 43–54. Petridis, P., 2013. Early Byzantine Pottery Of Greece, Gutenberg. p. 210 (in Greek). Polymeris, G.S., Afouxenidis, D., Raptis, S., Liritzis, I., Tsirliganis, N.C., Kitis, G., 2011. Relative response of TL and component-resolved OSL to alpha and beta radiations in annealed sedimentary quartz. Radiat. Meas. 46, 1055–1064. Raptis, K., 2012. Early Christian and Byzantine ceramic production workshops in Greece: typology and distribution. In Atti del IX Congresso Internazionale sulla Ceramica Medievale nel Mediterraneo, Venezia, 23–27 November 2009, pp. 38–44. Rathossi, C., 2005. Ancient ceramics from NW Peloponnese and the provenance of their raw materials: a petrographic, mineralogical, geochemical and archaeometric approach. Unpublished PhD thesis, University of Patras. (in Greek with English abstract). Rathossi, C., Tsolis-Katagas, P., Katagas, C., 2004. Technology and compositions of Roman pottery in Northwestern Peloponnese. Greece. Appl. Clay Sci. 24, 313–326. Rathossi, Ch., Kondopoulou, D., Tema, E., 2012. Archaeometric and Archaeomagnetic measurements on Greek ceramics and baked clays: a promising combination. 39th International Symposium on Archaeometry, 28 May–1 June 2012, Leuven, Belgium. Schnepp, E., Lanos, Ph., 2005. Archaeomagnetic secular variation in Germany during the past 2500 years. Geophys. J. Int. 163, 479–490. Spassov, S., Hus, J., 2006. Estimating baking temperatures in a Roman pottery kiln by rock magnetic properties: implications of thermochemical alteration on archaeointensity determinations. Geophys. J. Int. 167, 592–604. Tema, E., Kondopoulou, D., 2011. Secular variation of the Earth's magnetic field in the Balkan region during the last eight millennia based on archaeomagnetic data. Geophys. J. Int. 186, 603–614. Tema, E., Hedley, I., Lanos, Ph., 2006. Archaeomagnetism in Italy: a compilation of data including new results and a preliminary Italian secular variation curve. Geophys. J. Int. 167, 1160–1171. http://dx.doi.org/10.1111/j.1365-246X.2006.03150.x. Tema, E., Gómez-Paccard, M., Kondopoulou, D., Almar, Y., 2012. Intensity of the Earth's magnetic field in Greece during the last five millennia: new data from Greek pottery. Phys. Earth Planet. Inter. 202 (203), 14–26. Tema, E., Fantino, F., Ferrara, E., Lo Giudice, A., Morales, J., Goguitchaichvili, A., Camps, P., Barello, F., Gulmini, M., 2013a. Combined archaeomagnetic and thermoluminescence study of a brick kiln excavated at Fontanetto Po (Vercelli, Northern Italy). J. Archaeol. Sci. 40 (4), 2025–2035. Tema, E., Morales, J., Goguitchaichvili, A., Camps, P., 2013b. New archaeointensity data from Italy and geomagnetic field variation in the Italian peninsula. Geophys. J. Int. 193, 603–614. Tema, E., Polymeris, G., Morales, J., Goguitchaichvili, A., Tsaknaki, V., 2014. Dating of ancient kilns: a combined archaeomagnetic and thermoluminescence analysis applied to a brick workshop at Kato Achaia, Greece. J. Cult. Herit. http://dx.doi.org/10.1016/ j.culher.2014.09.013. Vieillevigne, E., Guibert, P., Bechtel, F., 2007. Luminescence chronology of the medieval citadel of Termez, Uzbekistan: TL dating of bricks masonries. J. Archaeol. Sci. 34, 1402–1416. Wagner, G.A., 1998. Age Determination Of Young Rocks And Artifacts: Physical And Chemical Clocks In Quaternary Geology And Archaeology. Springer–Verlag, Berlin Heidelberg. Zananiri, I., Batt, C., Lanos, Ph., Tarling, D., Linford, P., 2007. Archaeomagnetic secular variation in the UK during the past 4000 years and its application to archaeomagnetic dating. Phys. Earth Planet. Inter. 160 (2), 97–107. Zimmerman, D.W., 1971. Luminescence dating using fine grains from pottery. Archaeometry 13 (1), 29–56.