1992 Fiscal Year Final Research Report Summary
Studies to attain high accuracy in radiocarbon dating with AMS of sedimentary samples older than 30,000y.B.P.
| Project/Area Number |
03640656
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Nagoya University |
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Principal Investigator |
NAKAMURA Toshio Nagoya University, Dating and Materials Research Center, associate professor, 年代測定資料研究センター, 助教授 (10135387)
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| Co-Investigator(Kenkyū-buntansha) |
SAKAMOTO Toru Nagoya University, Graduate School of Human Informatics, professor, 人間情報学研究科, 教授 (80205773)
NAKAI Nobuyuki Nagoya University, School of Science, honorary professor, 名誉教授 (40022529)
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| Project Period (FY) |
1991 – 1992
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| Keywords | age measurement / radiocarbon dating / accelerator mass spectrometry / tandem accelerator / geochronology / tephrochronology / cross-dating / sample contamination |
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| Research Abstract |
Radiocarbon (^<14>C) dating with accelerator mass spectrometry (AMS) has enabled us to measure ages of geological samples as old as 40 to 60 ky.B.P. with a reasonable accuracy. This study has been organized to test the reliability of ^<14>C dates of 40 to 60 ky.B.P. The samples are collected in geological and geographical fields, mainly selected from well-defined horizons, i.e., those horizons identified by tephrochronology.
With this investigation, the followings have been clarified, concerning the age dating of old samples with a Tandetron accelerator mass spectrometer:
(1)^<14>C dates are consistent with sedimentary horizons, for ages from 40 to 60 ky.B.P.
(2)For ^<14>C dates beyond 60ky.B.P., a saturation of ^<14>C dates comes up, and ^<14>C dates are no more consistent with sedimentary sequences. The appearance of the plateau in ^<14>C dates is expected from the observation that dead graphite, which is too old to contain ^<14>C, showed apparent ^<14>C dates of 60 to 70 ky.B.P (average value: 65,080 y.B.P.).
^<14>C dates are compared with those dates measured by some other dating methods in this investigation. The ^<14>C dates of charcoal collected from Tokyo pumice flow deposits are compared with a fission-track date of obsidian collected from Tokyo pumice deposits, and the ^<14>C dates of charcoal from the Ontake volcanic deposits with a K-Ar age of lava covering the deposits. The comparisons showed a good agreement. Details of the experiments are given elsewhere. Consistency tests among different dating methods are one of the important themes to be performed intensively.
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