Publications

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2017
Shaar, R, Tauxe L, Goguitchaichvili A, Devidze M, Licheli V.  2017.  Further evidence of the Levantine Iron Age geomagnetic anomaly from Georgian pottery. Geophysical Research Letters. 44:2229-2236.   10.1002/2016gl071494   AbstractWebsite

Recent archaeomagnetic data from ancient Israel revealed the existence of a so-called "Levantine Iron Age geomagnetic anomaly" (LIAA) which spanned the first 350years of the first millennium before the Common Era (B.C.E.) and was characterized by a high averaged geomagnetic field (virtual axial dipole moments, VADM>140ZAm(2), nearly twice of today's field), short decadal-scale geomagnetic spikes (VADM of 160-185ZAm(2)), fast field variations, and substantial deviation from dipole field direction. The geographic constraints of the LIAA have remained elusive due to limited high-quality paleointensity data in surrounding locations. Here we report archaeointensity data from Georgia showing high field values (VADM>150ZAm(2)) in the tenth or ninth century B.C.E., low field values (VADM<60 ZAm(2)) in the twelfth century B.C.E., and fast field variation in the fifth and fourth centuries B.C.E. High field values in the time frame of LIAA have been observed so far only in three localities near the Levant: Eastern Anatolia, Turkmenistan, and now Georgia, all located east of longitude 30 degrees E. West of this, in the Balkans, field values in the same time are moderate to low. These constraints put geographic limits on the extent of the LIAA and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium B.C.E., comparable in area and magnitude (but of opposite sign) to the presently active South Atlantic anomaly.

2010
Shaar, R, Ron H, Tauxe L, Kessel R, Agnon A, Ben-Yosef E, Feinberg JM.  2010.  Testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material. Earth and Planetary Science Letters. 290:201-213.   10.1016/j.epsl.2009.12.022   AbstractWebsite

The Middle-Eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision. The purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions: 1) "Does slag material display the magnetic properties required for valid Thellier experiments?" and 2) "What is the accuracy of the archaeointensity estimates derived from Thellier-style experiments on optimal samples?" We address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in Thellier experiments. To address the second question, we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same 1721 paleointensity technique used for the ancient slag. Microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three-dimensional dendritic structures whose branches consist of submicronelongated particles. Magnetic analyses show that these dendrites behave as an assemblage of shape-controlled, single-domain-like particles and that their magnetization is thermoremanent. We conclude that slag material can be magnetically suitable for valid Thellier experiments. The laboratory-produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag. IZZI experiments showed that nonlinear TRM acquisition, even at field strengths similar to Earth's, and TRM anisotropy are important factors to monitor during paleointensity studies of slag material. Anisotropy and non-linearity are probably related to the dendritic shape of the oxide grains. Intensity estimates derived from three laboratory-produced slag samples demonstrated accuracy to within similar to 5% after applying the required corrections. (C) 2009 Elsevier B.V. All rights reserved.

2002
Bowles, J, Gee J, Hildebrand J, Tauxe L.  2002.  Archaeomagnetic intensity results from California and Ecuador: evaluation of regional data. Earth and Planetary Science Letters. 203:967-981.   10.1016/s0012-821x(02)00927-5   AbstractWebsite

We present new archaeointensity data for southeastern California (similar to33degreesN, similar to115degreesW, 50-1500 yr BP) and northwestern South America (Ecuador, 2.4degreesS, 80.7degreesW, 4000-5000 yr BP). These results represent the only data from California, as well as the oldest archaeointensity data now available in northwestern South America. In comparing our results to previously published data for the southwestern United States and northwestern South America, we note that significant scatter in the existing data makes comparisons and interpretations difficult. We undertake an analysis of the sources of data scatter (including age uncertainty, experimental errors, cooling rate differences, magnetic anisotropy, and field distortion) and evaluate the effects of scatter and error on the smoothed archaeointensity record. By making corrections where possible and eliminating questionable data, scatter is significantly reduced, especially in South America, but is far from eliminated. However, we believe the long-period fluctuations in intensity can be resolved, and differences between the Southwestern and South American records can be identified. The Southwest data are distinguished from the South American data by much higher virtual axial dipole moment values from similar to 0-600 yr BP and by a broad low between similar to 1000-1500 yr BP. Comparisons to global paleofield models reveal disagreements between the models and the archaeointensity data in these two regions, underscoring the need for additional intensity data to constrain the models in much of the world. (C) 2002 Elsevier Science B.V. All rights reserved.

1993
Pick, T, Tauxe L.  1993.  Holocene Paleointensities - Thellier Experiments on Submarine Basaltic Glass from the East Pacific Rise. Journal of Geophysical Research-Solid Earth. 98:17949-17964.   10.1029/93jb01160   AbstractWebsite

A complete description of the geomagnetic field requires both paleodirectional and paleointensity data. Although the paleointensity data base has grown steadily over the last three decades, it remains limited in time and space (the majority of data are of Holocene age and come from Europe). Furthermore, it has been difficult to assess the reliability of the paleointensity determinations. Here we present, paleointensity determinations on precisely dated Holocene (0 to 3500 years old) submarine basaltic glass from the East Pacific Rise (15-degrees-S to 22-degrees-S). Although hysteresis measurements and low-temperature isothermal remanent magnetization (IRM) acquisition experiments document a significant contribution of superparamagnetic grains, high blocking temperatures (above 400-degrees-C) and Curie temperatures between 490-degrees-C and 550-degrees-C indicate a single-domain low-Ti magnetite as the carrier of the remanent magnetization. This notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200-300 mT. Submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for Thellier experiments. Twenty-six out of 30 samples resulted in acceptable paleointensity determinations. Multiple experiments on splits from the same sample show good reproducibility. The paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery. The results of the remaining samples range from 16.7 to 53.9 muT with corresponding virtual axial dipole moments (VADM) of 3.61 X 10(22) to 11.9 X 10(22) A m2. The intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations. Basaltic glass is frequently recovered in both dredged and drilled material froin the ocean floor. The availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space.