[S-EM15] Geomagnetism and paleomagnetism

[SEM15-P17] Absolute paleointensities of the Laschamp excursion by the recent methods (Initial report)

*Takuya Sakaguchi¹, Nobutatsu Mochizuki² (1.Graduate School of Science and Technology, Kumamoto University, 2.Faculty of Advanced Science and Technology, Kumamoto University)

Keywords:geomagnetic excursion, absolute paleointensity, Tsunakawa-Shaw method, IZZI Thellier method, Laschamp

Absolute paleointensities in excursions are important for understanding the characteristics of the Earth dynamo. The intermediate directions, now widely known as the Laschamp excursion of 40,000 years ago, were first reported from two lavas and a scoria of the Chaîne des Puys in Massif Central, France. Roperch et al. (1988) reported an absolute paleointensity of 7.7±1.6µT for the Laschamp excursion by using the Thellier method with pTRM check. This value is often cited as a typical value of absolute paleointensity for an excursion. However, the reported data is not satisfied with the amount of data for each unit, because it was an average of 7 values, which consist of 2-3 measurements from each of the three different sites (Laschamp lava and scoria, and Olby lava). In addition, no subsequent studies have reported paleointensity results using the Tsunakawa-Shaw method, which can correct the effects of thermal alternation, or the IZZI Thellier method, which can detect non-ideal behaviors in the experiment, leaving room for reconsideration in terms of data quality.
Therefore, we are going to revisit absolute paleointensities of the Laschamp excursion by using these methods. In this study, oriented lava samples were collected from six lava in Chaîne des Puys for studying the Laschamp excursion and pre- and post-date fields. In this presentation, we report the initial results of thermomagnetic analysis, paleomagnetic direction, and paleointensity.