TY - JOUR
T1 - Reducing the age range of tsunami deposits by 14C dating of rip-up clasts
AU - Ishizawa, Takashi
AU - Goto, Kazuhisa
AU - Yokoyama, Yusuke
AU - Miyairi, Yosuke
AU - Sawada, Chikako
AU - Takada, Keita
N1 - Funding Information:
We would like to thank Prof. Jasper Knight and Dr. Catherine Chagué for their kind editing. We also thank Dr. Raphaël Paris and an anonymous reviewer for their valuable comments. Field surveys and sampling were performed as activities of the advisory committee for tsunami traces in Iwate Prefecture. We thank committee members and S. Kon for their kind support and advice related to this work. This research, which was supported by KAKENHI (26242033), was partly supported by the Program for Leading Graduate Schools, “Inter-Graduate School Doctoral Degree Program on Global Safety,” of the Ministry of Education, Culture, Sports, Science and Technology .
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2018/2
Y1 - 2018/2
N2 - Erosion by tsunami waves represents an important issue when determining the age of a tsunami deposit, because the age is usually estimated using dating of sediments above and below the deposit. Dating of material within the tsunami deposit, if suitable material is obtainable, can be used to further constrain its age. Eroded sediments are sometimes incorporated within the tsunami deposits as rip-up clasts, which might therefore be used as minimum age dating material. However, the single calibrated 14C age often shows a wide age range because of fluctuations in the calibration curve. Therefore, it remains uncertain whether rip-up clast measurements are useful to constrain the depositional age of tsunami deposits, or not. In this study, we carried out high-resolution 14C dating of tsunami deposits, including rip-up clasts of peat, in Rikuzentakata, northeastern Japan, where numerous rip-up clasts were observed within a tsunami deposit. Sediments above and below the tsunami deposit and a 5 cm large rip-up clast were dated sequentially. Comparison of these dating results with the calibration curve revealed that the clast was inverted. Its age was better constrained based on the stratigraphic order, and we infer that the clast corresponds to approximately 100 years of sedimentation. The oldest age of the clast was consistent with the age of the peat immediately below the tsunami deposit, suggesting that surface sediments probably formed the rip-up clast at the time of the tsunami. Thus, the dating of the rip-up clast was useful to further constrain the depositional age of the tsunami deposit, as we narrowed the tsunami deposit age range by approximately 100 years. Results show that ignoring tsunami-related erosion might lead to overestimation of the tsunami deposit age. For this reason, an appropriate dating site, which is less affected by minor tsunami-related erosion with regards to the paleo-topography, should be explored. We therefore propose a more effective sampling strategy for better age estimation of tsunami deposits.
AB - Erosion by tsunami waves represents an important issue when determining the age of a tsunami deposit, because the age is usually estimated using dating of sediments above and below the deposit. Dating of material within the tsunami deposit, if suitable material is obtainable, can be used to further constrain its age. Eroded sediments are sometimes incorporated within the tsunami deposits as rip-up clasts, which might therefore be used as minimum age dating material. However, the single calibrated 14C age often shows a wide age range because of fluctuations in the calibration curve. Therefore, it remains uncertain whether rip-up clast measurements are useful to constrain the depositional age of tsunami deposits, or not. In this study, we carried out high-resolution 14C dating of tsunami deposits, including rip-up clasts of peat, in Rikuzentakata, northeastern Japan, where numerous rip-up clasts were observed within a tsunami deposit. Sediments above and below the tsunami deposit and a 5 cm large rip-up clast were dated sequentially. Comparison of these dating results with the calibration curve revealed that the clast was inverted. Its age was better constrained based on the stratigraphic order, and we infer that the clast corresponds to approximately 100 years of sedimentation. The oldest age of the clast was consistent with the age of the peat immediately below the tsunami deposit, suggesting that surface sediments probably formed the rip-up clast at the time of the tsunami. Thus, the dating of the rip-up clast was useful to further constrain the depositional age of the tsunami deposit, as we narrowed the tsunami deposit age range by approximately 100 years. Results show that ignoring tsunami-related erosion might lead to overestimation of the tsunami deposit age. For this reason, an appropriate dating site, which is less affected by minor tsunami-related erosion with regards to the paleo-topography, should be explored. We therefore propose a more effective sampling strategy for better age estimation of tsunami deposits.
KW - Erosion
KW - Historical tsunami
KW - Radiocarbon dating
KW - Rip-up clast
KW - Sanriku coast
KW - Tsunami deposit
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U2 - 10.1016/j.sedgeo.2017.09.008
DO - 10.1016/j.sedgeo.2017.09.008
M3 - Article
AN - SCOPUS:85029909448
SN - 0037-0738
VL - 364
SP - 334
EP - 341
JO - Sedimentary Geology
JF - Sedimentary Geology
ER -