Reexamination of tephra correlations in the Karasuma Deep Core by the eastside of Lake Biwa, central Japan

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  • 烏丸地区深層ボーリングコアの火山灰対比の再検討
  • カラスマ チク シンソウ ボーリングコア ノ カザンバイ タイヒ ノ サイケントウ

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Abstract

The Karasuma Deep Core was drilled to a depth of about 900 m on the east shore of the southern part of Lake Biwa. The cores in 900 m are composed of fluvio-lacustrine sediments with 19 volcanic ash beds. Eight of these volcanic ashes were correlated with known volcanic ashes around/under Lake Biwa. Although the depositional age of the core was estimated based on the age of these correlated volcanic ashes, the age of the KR296 volcanic ash in the upper part of this core was pointed out as problematic because it does not fit the sedimentation rate curve of this core. In this study, volcanic ashes in this core are analyzed their chemical composition of volcanic glasses, and the correlations of volcanic ashes are reexamined based on these analyzed data. As the result, the previous correlation of the KR296 volcanic ash is turned out to be wrong and is correlated with another one. The volcanic ash in this core, the KR21, KR39E, KR229, KR296, KR335, KR454, KR563, and KR980 volcanic ash were correlated with each widespread tephra. These are the K-Ah, A-Tn, Aso-1, Yamanoshita, Mnt- Ks5, Se-Tg, Ss-Az, and Eb-Fukuda tephras, respectively. The sedimentation rate curve of this core is estimated by the ages of these tephras.

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