JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-EM Earth's Electromagnetism

[S-EM18] [EE] General Contributions in Geomagnetism, Paleomagnetism, and Rockmagnetism

Sun. May 21, 2017 9:00 AM - 10:30 AM 301B (International Conference Hall 3F)

convener:Hirokuni Oda(Institute of Geology and Geoinformation, Geological Survey of Japan, AIST), Nobutatsu Mochizuki(Priority Organization for Innovation and Excellence, Kumamoto University), Joshua M Feinberg(University of Minnesota), Myriam Annie Claire Kars(Center for Advanced Marine Core Research), Chairperson:Joshua Feinburg(University of Minnesota), Chairperson:Myriam Kars(Center for Advanced Marine Core Research), Chairperson:Hirokuni Oda(Institute of Geology and Geoinformation, Geological Survey of Japan, AIST)

10:00 AM - 10:15 AM

[SEM18-10] A paleomagnetic record across the Mammoth reversed subchron reconstructed from the upper Pliocene Anno Formation, Awa Group, central Japan

*Yuki Haneda1, Makoto Okada2 (1.Graduate School of Science and Engineering, Ibaraki University, 2.Department of Earth Sciences, Faculty of Scinece, Ibaraki University)

Keywords:Mammoth reversed subchron, Virtual Geomagnetic Polarity, Oxygen isotopic stratigraphy, Paleomagnetism

The Awa Group, distributed in the central Boso Peninsula, central Japan, is a suit of marine succession for contiguous paleomagnetic studies, because of its strong magnetization and abundant marine microfossils used for age constraints. In this study, we obtained a successive paleomagnetic record across the Mammoth reversed subchron from the upper Pliocene Anno Formation, Awa Group.
Rock samples for paleomagnetic and foraminiferal oxygen isotopic analyses were collected from the Shikoma River, Terao and Nagasaki sections in Futtsu city, Chiba. Mini cores with 1-inch diameter and hand-picked specimens with about 300 g by dry-weight were collected at 80 horizons at every 0.5-1.0 m stratigraphic interval.
We performed progressive alternating field demagnetization (pAFD), progressive thermal demagnetization (pThD) and various rockmagnetic analyses to extract primary components from the specimens and verify the stability of the remanence. The results for rockmagnetic analyses exhibit the most specimens have pseudo-single domain magnetites as the magnetic carrier of natural remanent magnetizations. We carried out the reversal tests, one of the field tests, and the data from both demagnetization methods are passed. Therefore, we calculated the Virtual Geomagnetic Polarity (VGP) by using the ChRMs from pThD, which exhibt a better result in the reversal test than pAFD.
The VGP path during ca. 3.35–3.19 Ma, including the Mammoth reversed subchron, was reconstructed. The VGPs across the upper and lower Mammoth boundaries are through the northeastern Africa and the southern Pacific off Chile, respectively. These VGP paths across the upper and lower Mammoth boundaries are similar to those from a sedimentary section in Sicily (Linssen, 1991) and from the Wai’anae volcano in Oahu (Herrero-Bervera et al., 1999; Herrero-Bervera and Valet, 2005).

References
Herrero-Bervera et al., 1999, Phys. Earth Planet. Int., 115(2), 119–135.
Herrero-Bervera, E., and J.-P. Valet, 2005, Earth Planet. Sci. Lett., 234(1), 279–296.
Linssen, J.H., 1991, Geol. Ultraictina, 80, 231 pp.