Stratigraphy and age of sediment cores from the Ubuka Basin in Abu monogenic volcanoes, western Honshu, Japan

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Other Title
  • 阿武単成火山群, 宇生賀盆地から採取したコア試料の層序と年代

Abstract

In the Abu monogenic volcanoes, lava flows/domes and the scoria cones are scattered at about 400 km2, and started activities from about 2 Ma. The Ubuka basin is surrounded by Gongenyama (ca. 0.31 Ma) on the south side, Takamureyama (ca. 0.18 Ma) on the north side, Nishidai and Higashidai (ca. 0.04 Ma) on the east side, and Horikoshi lava from Nabeyama scoria cone (-0.08 Ma) on the west side. Buried sediments cover a long range from the last glacial to the postglacial, but tephra such as Kikai-Akahoya (K-Ah) has not been detected. Many buried trees (5130-3676 cal BP) are occurred in the depth of 50 to 60 cm. In this study, to reveal the burial process of the basin, and estimate an eruption age of Nabeyama scoria cone, a total of 10 sediment cores (up to 710 cm in depth) were collected from eight sites in the basin. The facies observation, X-ray imaging, digital color measurement, initial magnetic susceptibility measurement measurement, mud content measurement, major-element compositional analysis of volcanic glass, and AMS 14C dating were performed. The sediment cores are gradually changed from the lowest silt and clay layer to the top of the peaty layers. A peaty layer (up to a depth of 180 cm) was found at only one site, and a bubble-wall type volcanic glass that could be correlated with the K-Ah tephra was detected. In the other seven sites, K-Ah could not be found and it is considered that there was sedimentation hiatus before and after K-Ah.

Journal

  • 名古屋大学年代測定研究

    名古屋大学年代測定研究 7 43-49, 2023-03

    Division for Chronological Research, Institute for Space‒Earth Environmental Research, Nagoya University

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