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.     

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.     

THE BRITISH ARCHAEOMAGNETIC CALIBRATION CURVE: AN OBJECTIVE TREATMENT

This paper examines the limitations and deficiencies of the current archaeomagnetic calibration curve in use in Britain and explores a different approach to its construction, drawing on recent advances in this subject, in particular the use of a weighted moving window method of averaging. The main advantage of this method is shown to be its ability to take into account uncertainties in both the magnetic direction and the archaeological date of data used in the calibration curve, leading to a secular variation curve with an associated error estimate. Hence, when dating a magnetic direction, the uncertainties in the calibration curve can be taken into account, as well as the uncertainties in the magnetic direction to be dated.     

Interpretation of the Thermogravimetric Curves of Ancient Pozzolanic Concretes

Pozzolanic concretes submitted to thermogravimetric (TG) analysis show a continuous weight loss starting from about 400 °C. In order to reconcile these observations with those from other analytical methods, it is necessary to attribute this weight loss to CO₂ removal. It has been proposed, in the literature, that silicates and CaCO₃ react at lower temperatures, producing calcium silicates and CO₂. In this paper, the FTIR spectra collected on samples submitted to TG analysis, stopped at conveniently selected temperatures, provide direct evidence that the continuous weight loss recorded with thermogravimetric analysis of the pozzolanic concrete in the temperature range 400–900 °C is to be attributed to the reaction between the silicates and calcite, with the formation of CO₂ and of a silicate that is richer in CaO. Therefore it is justifiable that the whole weight loss, in the temperature range 400–900 °C, should be taken into account in the calculation of the CaCO₃ content of the concrete. Moreover, the described procedure—of recovering small samples (2 mg) from the sample‐holder of the TG apparatus at various steps of the heating rate and comparing the FTIR spectra—can help in identifying the pozzolanic nature of a concrete that, in general, is not easily recognizable from the trend of the thermoanalytical curve.     

DISTINCT,LATE BRONZE AGE (c. 1650 bc) WALL‐PAINTINGS FROM AKROTIRI,THERA, COMPRISING ADVANCED GEOMETRICAL PATTERNS*

This paper studies a set of wall‐paintings of the Late Bronze Age (c. 1650 bc ) initially decorating the internal walls of the third floor of the edifice called ‘Xeste 3’, excavated at Akrotiri, Thera, whose restoration is now in progress. It deals with the methods used for the drawing of the geometrical figures appearing in these wall‐paintings. It is demonstrated that most of the depicted configurations correspond with accuracy to geometrical prototypes such as linear spirals and canonical polygons. It is pointed out that the steady lines of the figures, their remarkable repeatability, the precision of the geometrical shapes and their even distribution in the wall‐paintings indicate a very distinctive use of the ‘Xeste 3’ third floor, which is now investigated.     

OPTICAL DATING RESULTS FOR BRITISH ARCHAEOLOGICAL SEDIMENTS

In this paper optical dating results for a range of British archaeological sediments are presented to illustrate the potential this method offers for archaeologists. The optical dating is shown to offer an absolute method for directly dating the deposition of sediments for an age range of approximately 1–300ka. Problems have been found with recuperation of the optically stimulated luminescence signal and insufficient bleaching at deposition of the sediment. A suitable correction method for the recuperation has been found and a method of identifying insufficient bleaching is suggested.