14C wiggle-matching age of tree rings in the Towada-Hachinohe pyroclastic flow deposits

The Towada-Hachinohe pyroclastic flow is a non-welding dacitic to rhyolitic pyroclastic flow deposit (ca. 40 km3 in volume). The tephra (To-H) associated with this eruption is correlated with the volcanic glass NEEM1502.60m (22 grains) from the Greenland ice core, which has been dated to 15.7 ± 0.2...

Full description

Bibliographic Details
Main Authors: 坂田, 皓亮, Sakata, Kosuke, 奥野, 充, Okuno, Mitsuru, 藤木, 利之, Fujiki, Toshiyuki, 小林, 哲夫, Kobayashi, Tetsuo
Language:Japanese
Published: 名古屋大学宇宙地球環境研究所年代測定研究部 2022
Subjects:
AMS
Online Access:https://nagoya.repo.nii.ac.jp/record/2002922/files/022-026_2021.pdf
Description
Summary:The Towada-Hachinohe pyroclastic flow is a non-welding dacitic to rhyolitic pyroclastic flow deposit (ca. 40 km3 in volume). The tephra (To-H) associated with this eruption is correlated with the volcanic glass NEEM1502.60m (22 grains) from the Greenland ice core, which has been dated to 15.7 ± 0.2 ka b2k (2σ). In a nearby area, a buried forest lies directly beneath this tephra and radiocarbon (14C) dates of approximately 13 ka BP have been obtained. In addition, van der Plicht et al. (2012) obtained 16,534–16,204 cal BP (2σ) by wigglematching 34 14C ages from an approximately 350-year-old buried tree to the calibration dataset IntCal09. We matched them to the IntCal20 and obtain 15,775–15,710 cal BP (2σ) using the computer program Oxcal ver. 4.4. We measured ten 14C ages of buried tree (99 annual rings) collected from the pyroclastic flow deposits (40 °31'57.8"N, 141°11'30.8"E) with accelerator mass spectrometry (AMS) and obtained 14C ages of 13,338–13,137 BP. These 14C ages were matched with IntCal20 and yielded 15,886–15,774 cal BP (2σ). Assuming that the To-H age from the ice cores is the true (reliable) age, the matching ages with the IntCal09 are more than 500 years old. Comparing the matching results of matching with the IntCal20, a larger number of annual rings and measurement data, provides a narrower range of calendar date (i.e., higher precision). 十和田・八戸火砕流の噴火に伴うテフラ(To-H)は、グリーンランド氷床コアの火山ガラスNEEM1502.60m(22粒)に対比され、その年代は15.7±0.2kab2k(2σ)である。このテフラの直下には埋没林があり、約13kaBPの放射性炭素(14C)年代が得られている。Horiuchi et al.(2007)は、IntCal04との比較から約15.5calkaBPを、van der Plicht et al.(2012)は、樹齢約350年の樹木年輪の14C年代(34点)をIntCal09にマッチングして16,534–16,204calBP(2σ)を得ている。著者らは火砕流堆積物(40°31'57.8"N,141°11'30.8"E)中の樹木試料(直径14cm、年輪99枚)を加速器質量分析計(AMS)で測定し、10点の14C年代をIntCal20にマッチングしたところ15,886–15,774calBP(2σ)を得た。氷床コアのTo-H年代が真の(信頼できる)年代であると仮定すると、IntCal09とのマッチング(van der Plicht et al., 2012)は500年以上も古い年代が得られたことになる。IntCal20とのマッチング結果を比較すると、年輪数や測定データの多い方が暦年代の幅が絞られる(=高精度)ことがわかった。 departmental bulletin paper