The archaeointensity of the earth's magnetic field retrieved from Pampean ceramics (South America)

Abstract

Absolute intensity determinations using the Coe variant of the Thellier method have been carried out on some selected pottery fragments collected in the wetlands of the lower Paraná (Pampean region, Argentina) in order to construct the first archaeointensity master curve for South America. Associated radiometric ages range between 1640±70 and 730±70 bp. Twenty-one samples (five fragments) out of 46 studied (eight fragments) provided successful absolute intensity determinations. The fragment-mean archaeointensity values obtained in this study range from 21.9±2.3 to 42.6±5.4 μT, with corresponding virtual axial dipole moments (VADMs) ranging from 4.0±0.5 to 8.1±1.0 x 10 22Am 2. This corresponds to a mean VADM of (6.4±1.8)×10 22 Am 2. The synthetic record retrieved from southern Argentina and Brazil consists of 17 mean archaeointensities distributed between approximately ad 700 and ad 1700. The data set shows several distinct periods of fluctuations of quite large intensity. However, most data are concentrated into a relatively narrow time period from ad 950 to ad 1300. Three general features may be detected: the time intervals from about ad 950 to 1130 and 1350 to 1480 are characterized by quite monotonic increases of geomagnetic intensity, while some decrease is observed from ad 1150 to 1280. These variations may be speculatively correlated to climate changes over multi-decadal time scales. Important differences are observed between the data and the geomagnetic field predictions derived from recently reported global models, which reinforces the importance of regional reference curves for dating purposes.