A Revision to the U.S. Southwest Archaeomagnetic Master Curve

Recently, two problems have been recognized with the United States Southwest archaeomagnetic master curve (Eighmy, 1991; LaBelle & Eighmy, 1997; Sternberg, 1989). One of these problems, the damping problem, is inherent to the moving window method of curve construction proposed by Sternberg (1989). The other is due to the fact that the small number of independently dated virtual geomagnetic pole determinations available for the period between 900–1100 are not representative of secular variation during this period. The analyses presented here confirm the existence of these two problems and suggest that they distort the curve by less than 1·0° and between 1·0° and 2·0° respectively. Based on these findings, a new curve is proposed for the U.S. Southwest.     

ARCHAEOMAGNETIC DATING OF COPPER SMELTING SITE F2 IN THE TIMNA VALLEY (ISRAEL) AND ITS IMPLICATIONS FOR THE MODELLING OF ANCIENT TECHNOLOGICAL DEVELOPMENTS

Site F2 in the Timna Valley, Israel, is a small copper smelting site of ‘primitive’ technology, dated by its excavator to the Pottery Neolithic (sixth to fifth millennium bce ). This early date challenges the common view of the beginning of smelting technology in the Levant and has been contested by various scholars since its publication. In this study, we present results of archaeointensity experiments conducted on slag fragments from the site. The slag yielded an excellent ancient geomagnetic value (64.1 ± 1.1 μT) that, when compared to the Levantine master curve, suggests an age not older than the second millennium and most probably between the 13th and 11th centuries bce . In addition to demonstrating the applicability of geomagnetic archaeointensity experiments to independent dating of slag, we discuss the implications of the current results for the socio‐historical picture of the Timna Valley, and in particular for the way in which technological developments were previously modelled in the archaeometallurgical research on the region.     

ARCHAEOMAGNETIC FIELD INTENSITY DURING THE ROMAN PERIOD AT SIWA AND BAHRYN OASIS,EGYPT: IMPLICATIONS FOR THE FIDELITY OF EGYPTIAN ARCHAEOMAGNETIC DATA

A preliminary survey was conducted in Siwa and Bahryn Oasis to test the possible influence of various rock magnetic and experimental constraints on the fidelity of the Egyptian archaeomagnetic field record. Five potsherds from the Roman era, which lasted from 1981 bp to 1555 bp , have been investigated. Archaeologists dated the localities to ～1620 bp . Ten ceramic specimens, two of each potsherd, were subjected to archaeointensity determination, including tests for domain state effects, magnetic anisotropy and magnetic cooling rate dependency. Six successful archaeointensity determinations are obtained from three individual cooling units, revealing an average field value of 37.7 μT for the late Roman period in Siwa and Bahryn oasis, which is comparable to the present‐day field strength. The error propagation of the individual uncertainties related to all applied experimental techniques results in a maximum uncertainty estimate of 4.4 μT. The obtained field value is significantly smaller than early results and slightly smaller than some more recent determinations of the field intensity in Egypt. The difference is attributed to a combined effect of alteration, magnetic anisotropy and magnetic cooling rate dependencies. Along with other high‐quality data from the south‐east Mediterranean, our data suggest a field intensity minimum during the Egyptian Roman era.     

NEW ARCHAEOINTENSITY RESULTS FROM GREEK MATERIALS*

This paper reports palaeointensity results from Greek materials from EC and AD periods, recently obtained in the Sofia palaeomagnetic laboratory. The classical Thellier method was applied and of 26 specimens studied 20 gave acceptable results. The paper aims to compare the newly obtained results with previously published ones from Greece and neighbouring territories relating to the same period of time. The trend of palaeointensity obtained for the period 2900–1700 BC coincides well with the Bulgarian intensity variation curve, while the younger period, 1900–1200 BC, needs further investigation because of the contradictory results obtained by different authors. It is also established that the bricks from the church of Agios Ioannis are earlier than the date of the building's construction and are reused.     

AN ARCHAEOMAGNETIC STUDY OF POTTERY KILNS FROM BRÜHL-PINGSDORF (GERMANY)*

Four pottery kilns from Brühl-Pingsdorf (Germany) were dated by comparing their characteristic remanent magnetization with a curve of the palaeo-secular variation of the geomagnetic field. Archaeomagnetic results suggest last heating events between AD 775 and 1020. The archaeological evidence generally supports the relative temporal succession and the duration of use, but indicates that the kilns are about 150 years younger on average. Hence, a systematic offset between these independently developed chronologies must be considered. Rock magnetic parameters display radial variations through the kiln walls. These variations are controlled by the maximum temperature the rock was exposed to. These parameters were used to identify specimen which acquired a thermoremanent magnetization.     

EVIDENCE FOR CHURCH ORIENTATION BY MAGNETIC COMPASS IN TWELFTH-CENTURY DENMARK

The orientations of some 570 Romanesque churches (one-third of the total) from four regions in Denmark show significant differences in the claimed east-west orientation, being typically rotated 5-15° clockwise from true east-west. Magnetic declination was predominantly easterly between AD 1000 and 1600; the church deviations probably originate from sometimes using a magnetic compass, other simple and plausible causes for this ‘skewness’, for example orientation by the sun at specific periods of the year or astronomical alignment, being hard to design. Hence, some 25% of the churches were probably oriented by means of a magnetic compass. As a tool for dating, the orientations have not yet been successful due to statistical scatter. Church building in Denmark boomed in the twelfth century. The early history of the compass is somewhat uncertain. The first European reference known is from about 1190-1200, while the oldest Norse source is from about 1225 (Landnámabók), saying that the lodestone was not known before. Danish churches thus bring new information about the early use of the magnetic compass in Europe.     

ADDITIONAL ARCHAEOMAGNETIC DATA ON THE SOUTH-WEST USA MASTER GEOMAGNETIC POLE CURVE*

Archaeomagnetic dating in the American south-west is progressing rapidly in terms of both method and application. Of particular importance has been the creation of a master curve of geomagnetic direction change for the region. However, confirmation, extension and refinement of this curve are always welcome contributions to the technique. So, efforts are under way to accumulate a large body of well-dated virtual geomagnetic pole positions and document these through publication so that the basis for dating samples of unknown age can be evaluated. This article adds 23 new dated pole positions to the list discussed in Eighmy (1991) and reports the results of our experiments with refining the south-west USA master curve, especially the creation of a new south-west master curve, SWCV595.     

RESEARCH REPORT: MAGNETIC INVESTIGATIONS AND THE AGE OF A MEDIEVAL KILN AT KUNGAHÄLLA (SOUTH‐WEST SWEDEN)*

The results from a magnetic survey and archaeomagnetic investigation of a medieval brick kiln at Kungahälla in Bohuslän (south‐west Sweden) are reported. Detailed magnetic total field and magnetic gradient measurements over known traces of the kiln showed marked local magnetic anomalies of up to 200 nT, revealing the rectangular shape of the kiln remains. Palaeomagnetic investigations of the remanent magnetization of 12 bricks from the kiln floor gave precise definitions of both the direction of the archaeomagnetic field [(D_m, I_m) = (66.7°, 8.8°), k = 655, α₉₅= 1.7°] and the palaeointensity [B_m= 69.0 ± 3.6 µT]. An archaeomagnetic date is obtained by comparing the direction of the archaeomagnetic field found in the kiln with a geocentral dipole‐transformation of the British master‐curve for secular variation. Of two possible archaeomagnetic dates (ad 1280 ± 50 or ad 1480 ± 50), the ad 1280 ± 50 age is in good accordance with the C‐14 ages and archaeological dates as well as with direct historical evidence, whereas a c. 100 years younger TL date appears to be too young.     

ARCHAEOMAGNETISM IN ARCHAEOMETRY— A SEMI‐CENTENNIAL REVIEW*

The journal Archaeometry and its first co‐editor Martin Aitken played key roles in the development of archaeomagnetism. This paper briefly reviews all papers published in Archaeometry, and a few others, dealing with archaeomagnetic secular variation, archaeomagnetic dating, archaeointensity studies and related applications of magnetic studies to archaeology, to indicate some of the major developments over the past 50 years.