Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating
Much interest and activity is presently centred on the stratigraphic use of tephra. Distinctive tephra layers constitute important time-parallel markers, which if widespread, offer the potential for reliable correlation over long distances. Furthermore, they provide valuable geochrono-logical contro...
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ftuninewbrunojs:oai:ojs.journals.lib.unb.ca:article/3198 2023-05-15T13:39:01+02:00 Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating Westgate, John A. Briggs, Nancy D. 1980-04-04 application/pdf https://journals.lib.unb.ca/index.php/GC/article/view/3198 eng eng Geological Association of Canada https://journals.lib.unb.ca/index.php/GC/article/view/3198/3715 https://journals.lib.unb.ca/index.php/GC/article/view/3198 Copyright (c) 2015 Geoscience Canada Geoscience Canada; Volume 7, Number 1 (1980) 1911-4850 0315-0941 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion research-article 1980 ftuninewbrunojs 2022-07-11T11:47:19Z Much interest and activity is presently centred on the stratigraphic use of tephra. Distinctive tephra layers constitute important time-parallel markers, which if widespread, offer the potential for reliable correlation over long distances. Furthermore, they provide valuable geochrono-logical control for their age can be determined by several radiometric methods. Confident correlations require a multiple criteria approach to tephra characterisation; samples should only be considered equivalent if their stratigraphic, palaeontologic, palaeomagnetic, and radiometric age relations are compatible and the physico-chemical properties of their glass shards and phenocrysts agree. Special attention should be given to the possibility of resedimentation into a younger stratigraphic position. Because grain-discrete methods of analysis are sensitive to contamination effects, they are to be preferred over those methods that require use of bulk separates. Coarse, proximal tephra can be reliably dated by the K-Ar method as pure mineral separates can be readily isolated, but distal ash-grade tephra is better dated by the fission-track method in which ages are based on tracks counted in individual grains so that detrital contaminants can be easily recognised and avoided. The recent successful application of the fission-track method to distal tephra has resulted in a greatly improved understanding of the late Cenozoic geochronology of areas remote from volcanic centres. Tephrochronology is a useful tool in many areas of Quaternary research; in particular, it will undoubtedly continue to play an important role in the connection of marine and continental sequences, refinement of the palaeomagnetic chronology, calibration of hominid evolution in eastern Africa and other areas, and age-definition of Antarctic and Greenland ice cores. Article in Journal/Newspaper Antarc* Antarctic Greenland Greenland ice cores University of New Brunswick: Centre for Digital Scholarship Journals Antarctic Greenland |
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Open Polar |
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University of New Brunswick: Centre for Digital Scholarship Journals |
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ftuninewbrunojs |
language |
English |
description |
Much interest and activity is presently centred on the stratigraphic use of tephra. Distinctive tephra layers constitute important time-parallel markers, which if widespread, offer the potential for reliable correlation over long distances. Furthermore, they provide valuable geochrono-logical control for their age can be determined by several radiometric methods. Confident correlations require a multiple criteria approach to tephra characterisation; samples should only be considered equivalent if their stratigraphic, palaeontologic, palaeomagnetic, and radiometric age relations are compatible and the physico-chemical properties of their glass shards and phenocrysts agree. Special attention should be given to the possibility of resedimentation into a younger stratigraphic position. Because grain-discrete methods of analysis are sensitive to contamination effects, they are to be preferred over those methods that require use of bulk separates. Coarse, proximal tephra can be reliably dated by the K-Ar method as pure mineral separates can be readily isolated, but distal ash-grade tephra is better dated by the fission-track method in which ages are based on tracks counted in individual grains so that detrital contaminants can be easily recognised and avoided. The recent successful application of the fission-track method to distal tephra has resulted in a greatly improved understanding of the late Cenozoic geochronology of areas remote from volcanic centres. Tephrochronology is a useful tool in many areas of Quaternary research; in particular, it will undoubtedly continue to play an important role in the connection of marine and continental sequences, refinement of the palaeomagnetic chronology, calibration of hominid evolution in eastern Africa and other areas, and age-definition of Antarctic and Greenland ice cores. |
format |
Article in Journal/Newspaper |
author |
Westgate, John A. Briggs, Nancy D. |
spellingShingle |
Westgate, John A. Briggs, Nancy D. Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
author_facet |
Westgate, John A. Briggs, Nancy D. |
author_sort |
Westgate, John A. |
title |
Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
title_short |
Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
title_full |
Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
title_fullStr |
Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
title_full_unstemmed |
Dating Methods of Pleistocene Deposits and Their Problems: V. Tephrochronology and Fission-Track Dating |
title_sort |
dating methods of pleistocene deposits and their problems: v. tephrochronology and fission-track dating |
publisher |
Geological Association of Canada |
publishDate |
1980 |
url |
https://journals.lib.unb.ca/index.php/GC/article/view/3198 |
geographic |
Antarctic Greenland |
geographic_facet |
Antarctic Greenland |
genre |
Antarc* Antarctic Greenland Greenland ice cores |
genre_facet |
Antarc* Antarctic Greenland Greenland ice cores |
op_source |
Geoscience Canada; Volume 7, Number 1 (1980) 1911-4850 0315-0941 |
op_relation |
https://journals.lib.unb.ca/index.php/GC/article/view/3198/3715 https://journals.lib.unb.ca/index.php/GC/article/view/3198 |
op_rights |
Copyright (c) 2015 Geoscience Canada |
_version_ |
1766114067514130432 |