Stephanie Cai

© 2015. American Geophysical Union. All Rights Reserved. We have carried out an archaeomagnetic study on a late Neolithic locality in Sichuan, southwestern China. We pull together various dating techniques, including radiocarbon analysis, optically stimulated luminescence dating, stratigraphic information as well as archaeological and archaeomagnetic estimations, to constrain the age of the studied samples. Rock magnetic results indicate thermally stable fine-grained magnetite or titanomagnetite as the dominant magnetic carriers. More than half of the specimens in the paleointensity experiment pass the selection criteria and are considered to record robust intensity values. The virtual axial dipole moments range from approximately ×10 22 Am 2 with an average of 5.9×10 22 Am 2, indicating that the geomagnetic intensity around 3000 before the Common Era is overall lower than the present field intensity of this area. The new results from Liujiazhai are generally consistent with the published data of similar age but deviate from the only available model of CALS10k.1b at certain time periods, making them important for future improvements of the model. Those data are significant for constraining the variation of geomagnetic field intensity between ~3100 and 2600 B.C.E. and improving the regional model of eastern Asia.

In this study, we have carried out paleointensity experiments on 918 specimens spanning the last ~7 kyr, including pottery fragments, baked clay and slag, collected from Shandong, Liaoning, Zhejiang and Hebei Provinces in China. Approximately half of the specimens yielded results that passed strict data selection criteria and give high-fidelity paleointensities. The virtual axial dipole moments of our sites range from ~2×1022 to ~13×1022 Am2. At ~2250 BCE our results suggest a paleointensity low of ~2×1022 Am2, which increases to a high of ~13×1022 Am2 by ~1300 BCE. This rapid six-fold change in the paleointensity may have important implications for the dynamics of core flow at this time. Our data from the last ~3 kyr are generally in good agreement with the ARCH3k.1 model, but deviate significantly at certain time periods from the CALS3k.4 and CALS10k.1b model, which is likely due to differences in the data used to constrain these models. At ages older than ~3 ka, where only the CALS10k.1b model is available for comparison, our data deviate significantly from the model. Combining our new results with the published data from China and Japan, we provide greatly improved constraints for the regional model of Eastern Asia. When comparing the variations of geomagnetic field in three global representative areas of Eastern Asia, the Middle East and Southern Europe, a common general trend of sinusoidal variations since ~8 ka is shown, likely dominated by the dipole component. However, significant disparities are revealed as well, which we attribute to non-dipolar components caused by movement of magnetic flux patches at the core-mantle boundary. © 2014 Elsevier B.V.