New Archaeointensity Result from Middle-Eastern China and Its Constraints on the Variation of the Geomagnetic Field during the last 6 kyr

Abstract:

Archaeomagnetic study is an effective way to understand the variation of the geomagnetic field over periods of hundreds to thousands of years. We have carried out archaeointensity studies on archaeological artifacts, including pottery fragments, bricks and baked clay, collected from several sites covering the middle to eastern part of China spanning the past ~6 kyr. We designed detailed rock magnetic and archaeointensity experiments in this study. Rock magnetic results indicate that the main magnetic carriers of these samples are stable magnetite or titanomagnetite with mainly fine particles of SD and SP. About 40% of the specimens in the paleointensity experiment pass the strict selection criteria and are considered to record robust intensity values. The virtual axial dipole moments (VADMs) of our sites range from ~2.5×10²² to ~15.8×10²² Am². We record three low intensity values with VADMs of less than 3×10²² Am², two of them comparable to the one reported by Cai et al. (2015) at ~3000 BCE while the other one comparable to those reported by Cai et al. (2014) at ~2200 BCE, which supply further evidence for the existence of ‘DIPs’ (decreases in paleoinetnsity) in China during the period of ~3000-2000 BCE. A high intensity value of ~16×10²² Am² is recorded by our new data at ~1300 BCE, which may represent a new spike at this time period. The low and high values recorded by our new data update the six-fold variation between ~2200 BCE and ~1300 BCE discussed in Cai et al. (2014) to eight-fold, which may indicate a stronger geodynamic process during this period. Our new data are generally in good agreement with the published data in China, Japan and Korea at similar time periods, except the extreme low and high values discussed above, which will improve the Eastern Asian model greatly. The new data together with the published data suggest severe fluctuation of the geomagnetic field in Eastern Asia during the last 6 kyr. Vast quantities of reliable data are needed to further constrain the detailed variation of the field. When comparing with the global models, the new data fit well to the ARCH3k.1 model generally, but deviate from the CALS3k.4 and CALS10k.1b models at certain time periods (especially at ages older than ~3 ka), which make them significant for future improvements of the models.