| dc.description.abstract | Global geomagnetic field models (e.g. CALS10K, SHA.DIF.14K, pfm9k.1) are predominantly based on data from the Northern hemisphere, while also observations of the field become increasingly sparse going further back in time. Therefore, more data from especially the Southern hemisphere is required to improve our understanding of the geomagnetic field. In this study we aimed to obtain absolute archeointensities of the geomagnetic field in Suriname on unoriented archeological potsherds from six different levels of the Wageningen-1 mound, Hertenrits Culture, dated between 1145 ± 25 and 1310 ± 30 BP (655 to 975 AD). On representative shards from each level rock magnetic analyses and thermal demagnetization experiments have been carried out. Archeointensity analyses have been performed using the IZZI-Thellier method (Tauxe and Staudigel, 2004) on samples from all six levels, using the 2G DC SQUID system at Fort Hoofddijk (Utrecht University) and by the Microwave-Thellier method on subsamples that had a relatively high magnetic moment (levels 4 – 6) and were stable to microwave demagnetization, using the 14 GHz system at University of Liverpool. Laboratory alteration was monitored by pTRM checks and pTRM Tail checks (Riisager and Riisager, 2001). Average archeointensities between 10.52 ± 0.75 μT and 16.18 ± 2.16 μT were obtained using the conventional Thellier method; these values are three to four times lower than expected from geomagnetic field models. From these field models, i.e. SHA.DIF.14K (Pavón-Carrasco et al., 2014) and pfm9k.1 (Nilsson et al., 2014), archeointensities ranging from 37.01 ± 0.89 to 45.79 ± 0.93 and 37.6 ± 3.68 to 40.7 ± 3.21 respectively, are predicted. Besides by chemical alteration (e.g. Coe, 1967b) or the presence of a multidomain component (McClelland et al., 1996), the archeointensity results may have been biased by cooling rate effects (Dodson and McClelland-Brown, 1980; McClelland, 1984) and or by remanence anisotropy (Selkin et al., 2000). The latter have not been tested in this study. Only three out of 27 Microwave-Thellier measurements passed the set of criteria, yielding an average of 40.4 ± 3.7 μT (for 715 to 975 AD); these values are consistent with values expected from the geomagnetic models, but they seem fortuitous. To support our low, but high-quality IZZI-Thellier data and enhance the reliability of the geomagnetic models, definitely more paleomagnetic research is required over a larger time period and other regions around the equator and especially on the Southern hemisphere, preferably incorporating full vector analysis. | |
