Fission Track Ages of Eleven Quaternary Tephras in North Kanto and South Tohoku Regions, Central Japan.

DOI Web Site 25 Citations 27 References

Bibliographic Information

Other Title
  • 関東北部から東北南部に分布する第四紀テフラのフィッション・トラック年代
  • カントウ ホクブ カラ トウホク ナンブ ニ ブンプ スル ダイ4キ テフラ

Search this article

Abstract

A large number of Quaternary tephra layers covering terrace surfaces and hill slopes are well preserved in the north Kanto and south Tohoku regions of central Japan. However, previous fission track ages of some of the tephras are considered to be inaccurate, and other radiometric ages dated by K-Ar method reported in previous studies are also insufficient to discuss the tephrochronology.<br>In this study, eleven Quaternary tephra layers were newly dated by the fission track dating method using zircon crystals. The method includes zeta calibration, which is recommended by the I. U. G. S. The ages obtained are shown as follows, in descending order of the stratigraphy; Shibahara Tephra (SB): 110±20ka, Tagashira Tephra (TG): 160±20ka, APm-U: 130±30ka, Kurodahara Tephra (KdP): 200± 30ka, Nemoto 13 Tephra (Nm-13): 290±60ka, Nemoto 14 Tephra (Nm-14): 290±30ka, Nemoto 16 Tephra (Nm-16) 290±70ka, Tajima Yellow Tephra (TyP): 160±70ka, Hoshitoge Biotite Tephra (HtB): 660±40ka, Nishigo Pyroclastic Flow Deposit (NSG): 790±160ka, Kumado Pyroclastic Flow Deposit (KMD): 1, 400±200ka (errors are 1σ). SB, TG, KdP, Nm-14, HtB were dated using more than 100 zircon grains in order to obtain a high precision, but the remainding procedures used about 30 grains. The fission track ages are reviewed with reference to stratigraphic position, comparison with previous radiometric ages, and consistency with a chronological framework established by previous studies.<br>All the ages are consistent with the stratigraphic relationships of tephras except for TyP. Fission track ages determined in this study show younger ages than those obtained by the previous studies which did not use the zeta calibration. Our chronological data provide a new time scale for the tephrochronology of the study area. This suggests that changes in the accumulation rate of tephric soil deposits are smaller than estimated by Suzuki (1993). Climatic fluvial terraces formed under glacial conditions of marine isotope stage 6 are now recognizable, in contrast to previous studies. On the other hand, identification of APm-U tephra, correlated to Omachi A Tephra Group, requires further examination.

Journal

Citations (25)*help

See more

References(27)*help

See more

Keywords

Details 詳細情報について

Report a problem

Back to top