Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

H (Human Geosciences ) » H-QR Quaternary research

[H-QR05] Quaternary, Diachronic dynamics of human-environment interactions

Sun. May 26, 2019 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Mamoru Koarai(Earth Science course, College of Science, Ibaraki University), Ken Ikehara(Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology), Masayuki Hyodo(Research Center for Inland Seas, Kobe University)

[HQR05-P05] Comparison of geological stratigraphy between three drilling cores and analysis of shallow geological structure in the Koriyama Basin, Northeast Japan

*Takeshi ISHIHARA1, Takehiko Suzuki2 (1.Advanced Industrial Science and Technology, 2.Tokyo Metropolitan University)

Keywords:Koriyama Basin, drilling core, subsurface geological stratigraphy, tephra

1. Introduction
The Fukushima Renewable Energy Institute, AIST (FREA) has surveyed shallow subsurface geological analysis (ca. 100 m depth) in the Koriyama basin as part of researches to compile a suitability map for installation of ground source heat pump system. Ishihara et al. (2018) reported geological stratigraphy of an all-cores (GS-KR2015K-1, 251.60 m asl, 100 m depth) in the central part of the Koriyama basin and Kasahara et al. (2017) reported a tephro-stratigraphy of KR-11-1 core drilled in the northern part of the basin. In this study the authors reported geological stratigraphy of a new all-core (GS-KRC-1, 249.4 m asl, 80 m depth) in the southern part of the Koriyama basin and consider the shallow subsurface geological structure of the basin.

2. GS-KRC-1 core
Lithofacies: In the depth from surface to 29 m, silt and sandy-silt beds are dominant. Gravel layers are also intercalated at 3-8 m, 13.5-14.0 m, and 18-24 m depth. A tephra layer (volcanic glass ~ pumice sand beds) is detected from 27.0-27.4 m depth. Facies from 29 to 80 m mainly consist of gravel layer and a pyroclastic flow sediment is intercalated at 52-65 m depth.
Dating result: Two radiocarbon ages of wood fragments obtained from the core (1.78 and 2.12 m depth) show ca. 50,000 cal yBP, respectively. A FT age of pyroclastic flow sediment (55-59 m depth) shows 3.4±0.4Ma.

3. Discusstion
Based on stratigraphic correlation between GS-KRC-1 and other two cores (GS-KR2015-1 and KR-11-1), it was interpreted that silty-dominant layers with a depth of 0-29 m is the upper Koriyama Formation and gravel layers with a depth of 29-52 m is the lower Koriyama Formation or the Shirakawa Formation, respectively. The age of the pyroclastic flow sediment is well correlated with the age of the pyroclastic flow sediment (3.2 ± 1.3Ma) of GS-KR2015-1 (41.9-49.0 m depth), indicated that they are the same pyroclastic flow sediments.
The pyroclastic flow sediments of the GS-KRC-1 core is distributed at about 184.4-197.4 m asl, which its base level is 10 m lower than the pyroclastic flow sediment of the GS-KR2015-1 (202.6-209.7 m asl). It is indicated that terrace or hilly landform existed just before deposition of the pyroclastic flow sediments.