Paleointensity determination of welded tuffs extruded with tephra layers: A new approach to calibration of relative paleointensity stacks

For a reliable calibration of a relative paleointensity stack, we proposed a new method for direct comparison of absolute paleointensities (APIs) with relative paleointensities (RPIs) (Mochizuki et al., under review). In the analysis, APIs are directly compared with the RPIs of a RPI stack at six stratigraphic levels: three levels are based on tephrostratigraphic correlations between welded tuffs and corresponding tephra layers in the oxygen isotope stratigraphy, and the other three levels are based on paleomagnetic correlations between RPI minima and transitional geomagnetic fields. In the present study, to increase API data with tephrostratigraphic correlation, we applied the LTD-DHT Shaw paleointensity method (Tsunakawa-Shaw method) to 21 welded tuffs in Japan extruded with widespread tephra layers. We obtained mean paleointensities for 16 of the 21 welded tuffs. Since nine of the 16 welded tuffs were correlated with the tephras recognized in the oxygen isotope stratigraphy, they can be added to the API data used in the direct comparison method. Combining these API data with the reported data, we compared API data with RPIs from the PISO-1500 stack and SINT-800 stack at the 14 stratigraphic levels: eleven levels are based on tephrostratigraphic correlation and the other three levels are based on paleomagnetic correlation. RPIs of the PISO-1500 stack showed a linear relationship with the virtual axial dipole moments (VADMs) calculated from the APIs, indicating that the PISO-1500 stack has a linear relation to the axial dipole moment. PRIs from the SINT-800 stack also have a linear-like trend with the VADMs. This direct comparison method can clarify the relationship between APIs and RPIs of a RPI stack, and thus provide a reliable calibration of the RPI stack to absolute values.