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Abstract
Archaeointensity data have been obtained successfully using the Thellier-Coe protocol from twelve potsherds recovered from the vicinity of the “Piramide del Sol”, Teotihuacan, Mexico. In order to understand the magnetic behavior of the samples, we have conducted low-field versus temperature (k-T) experiments to determine the magnetic carriers of the pre-Columbian artefacts, as well as Saturation Isothermal Remanent Magnetization (SIRM), hysteresis loops and back-fields TESTS. The Curie temperatures indicate the presence of at least three magnetic mineral phases (238°C - 276°C, 569°C - 592°C, and 609°C - 624°C). The predominant Curie temperatures for these samples are typical of Ti-poor magnetite. The results of the magnetic grain size analyses indicate that if the magnetic mineral in a sample is only magnetite, the distribution on the modified Day et al. (1977) diagram yields specimens in the Single (SD), Pseudo (PSD) and Superparamagnetic (SP) domain ranges. The successfully absolute paleointensity determinations in this study using the Thellier-Coe protocol have yielded an average paleointensity of 38.871 +/- 1.833 m-Teslas (N = 12), and a virtual geomagnetic dipole moment of 8.682 +/- 0.402 × 1022 A/m2 which is slightly lower than the present field strength and which corresponds to an age interval between 500 and 430 AD. Thus, our results correlate well with the recently published CALS3K.4 curve and the incipient archaeointensity reference curve for the Mesoamerican paleo-field results. Therefore, the age of the artefacts would correlate well with absolute the early classic Teotihuacan cultural period.
Highlights
It is well known that archeomagnetic determinations are important contributions to constraining the global and local variations of the Earth’s magnetic field in the recent past
Various methods have been suggested to select the appropriate data for absolute paleointensity interpretation (PI) of the results despite the fact that much debate questions what constitutes acceptable PI determinations
In the best of cases, it is necessary for the samples in question to have reversible Curie point determination curves, which in a certain way give evidence that no apparent magnetomineralogical changes/alterations have occurred during the laboratory heating procedure, and for samples to be characterized by either single domain or an admixture of Pseudo Single and Single Domains (PSD/SD) magnetic grain sizes
Summary
It is well known that archeomagnetic determinations are important contributions to constraining the global and local variations of the Earth’s magnetic field in the recent past (e.g. present back to ~6000 years, e.g. Valet, Herrero-Bervera, LeMouël, & Plenier, 2008). Since the intensity of magnetization is a scalar quantity, it is not necessary to have the collected artefacts oriented This allows one to experiment with a technique used for unique and single objects, such as pottery shards that have been found in their original firing position. Archeomagnetic studies of in situ structures such as pieces of pottery, ovens, kilns and hearths of dissimilar ages allow us to reconstruct the changes in direction and intensity of the Earth’s magnetic field for a given geographical region In this study we have undertaken absolute paleointensity determinations of un-oriented potshards from the Teotihuacan Pyramids close to Mexico City in order to determine the strength of the magnetic field of the Earth recorded at the last time of firing of the pieces of pottery under question
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