[S-EM16] Geomagnetism, paleomagnetism, and rock magnetism

[SEM16-P04] A preliminary result of paleomagnetic measurement for the middle Miocene–lower Pleistocene lacustrine Idaho Group, Idaho State, USA

*Yuki Haneda¹, Megumi Saito-Kato², Tatsuya Hayashi³, William Krebs (1.Geological Survey of Japan, AIST, 2.National Museum of Nature and Science, Tokyo, 3.Kyusyu University)

Keywords:Magnetostratigraphy, fossil diatom, lacustrine sediment

The lacustrine–fluvial Idaho Group is distributed in the Western Snake River Basin, western Idaho State, USA. The Idaho Group consists mainly of diatomaceous siltstones, sandstones, and basaltic–rhyolitic volcanic ash beds, yielding radiometric ages between the Middle Miocene and the Early Pleistocene. The continuous and well exposed lacustrine sequence can provide an opportunity to elucidate the evolution of continental planktonic diatoms from the Middle Miocene to the Early Pliocene. However, the age constraint of the Idaho Group independent from the diatom biostratigraphy is still poor. Previous paleomagnetic studies on outcrops and a borehole core reported that the upper Idaho Group contains the Cochiti Normal Subchronozone and the Gauss–Matuyama boundary, but the age constraint for the lower part of the group depends on the sparse radiometric dating. We conducted a field survey in western Idaho in September 2024 and collected rock samples for fossil diatom and paleomagnetic analyses and volcanic ash samples for radiometric dating to construct diatom biostratigraphy of the Idaho Group. In this presentation, we show preliminary results of paleomagnetic and rock-magnetic measurements for the Idaho Group.