On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172
SUMMARY Palaeomagnetic secular variation (PSV) and excursion data obtained across MIS 8 (243–300 ka) from the western North Atlantic Ocean ODP (Ocean Drilling Program) sites 1060–1063 show composite high-resolution PSV records (both directions and relative palaeointensity) developed for each site an...
Published in: | Geophysical Journal International |
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Language: | English |
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Oxford University Press (OUP)
2020
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Online Access: | http://dx.doi.org/10.1093/gji/ggaa564 http://academic.oup.com/gji/advance-article-pdf/doi/10.1093/gji/ggaa564/34460930/ggaa564.pdf http://academic.oup.com/gji/article-pdf/225/2/1129/36563841/ggaa564.pdf |
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croxfordunivpr:10.1093/gji/ggaa564 2023-05-15T17:36:58+02:00 On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 Lund, Steve Acton, Gary Clement, Brad Okada, Makoto Keigwin, Lloyd 2020 http://dx.doi.org/10.1093/gji/ggaa564 http://academic.oup.com/gji/advance-article-pdf/doi/10.1093/gji/ggaa564/34460930/ggaa564.pdf http://academic.oup.com/gji/article-pdf/225/2/1129/36563841/ggaa564.pdf en eng Oxford University Press (OUP) https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model Geophysical Journal International volume 225, issue 2, page 1129-1141 ISSN 0956-540X 1365-246X Geochemistry and Petrology Geophysics journal-article 2020 croxfordunivpr https://doi.org/10.1093/gji/ggaa564 2022-04-15T06:16:44Z SUMMARY Palaeomagnetic secular variation (PSV) and excursion data obtained across MIS 8 (243–300 ka) from the western North Atlantic Ocean ODP (Ocean Drilling Program) sites 1060–1063 show composite high-resolution PSV records (both directions and relative palaeointensity) developed for each site and intercompared. Two methods of chronostratigraphy allow us to date these records. First, we used published results that compared the calcium carbonate records of ODP Leg 172 sediments and tuned them with Milankovich cyclicity. We also compared our palaeointensity records with the PISO-1500 global palaeointensity record that was dated with oxygen isotope stratigraphy. We prefer the PISO-1500 record to date our cores. Two excursions are preserved in our PSV records—Excursions 8α and 9α. Our revised age estimates for both excursions are 8α (236.7–239.8 ka) and 9α (283.7–286.9 ka). We have compared shipboard measurements of the two excursions with u-channel measurements of selected excursion intervals. Excursion 8α is interpreted as a ‘Class II’ excursion (local reversal) with in-phase inclination and declination changes; Excursion 9α is a ‘Class I’ excursion with 90° out-of-phase inclination and declination changes. Averaged directions (after removal of true excursional directions) and relative palaeointensity in 3 and 9 ka overlapping intervals show significant PSV directional variability over 104 yr timescales that is regionally correlatable among the four sites. A notable pattern of angular dispersion variability involves most time spent with low (∼10°) dispersion, with three shorter intervals of high (∼25°) dispersion. The relative palaeointensity variability also shows significant variability over 104 yr timescales with three notable intervals of low palaeointensity in all four records and a direct correspondence between the three low-palaeointensity intervals and the three intervals of high angular dispersion. The two magnetic field excursions occur in two of the three low-palaeointensity/high-dispersion intervals. This suggests that the geomagnetic field operates in two states between reversals, one with regular to high palaeointensity and low directional variability and one with low palaeointensity and significantly higher directional variability and excursions. Article in Journal/Newspaper North Atlantic Oxford University Press (via Crossref) Geophysical Journal International 225 2 1129 1141 |
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Open Polar |
collection |
Oxford University Press (via Crossref) |
op_collection_id |
croxfordunivpr |
language |
English |
topic |
Geochemistry and Petrology Geophysics |
spellingShingle |
Geochemistry and Petrology Geophysics Lund, Steve Acton, Gary Clement, Brad Okada, Makoto Keigwin, Lloyd On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
topic_facet |
Geochemistry and Petrology Geophysics |
description |
SUMMARY Palaeomagnetic secular variation (PSV) and excursion data obtained across MIS 8 (243–300 ka) from the western North Atlantic Ocean ODP (Ocean Drilling Program) sites 1060–1063 show composite high-resolution PSV records (both directions and relative palaeointensity) developed for each site and intercompared. Two methods of chronostratigraphy allow us to date these records. First, we used published results that compared the calcium carbonate records of ODP Leg 172 sediments and tuned them with Milankovich cyclicity. We also compared our palaeointensity records with the PISO-1500 global palaeointensity record that was dated with oxygen isotope stratigraphy. We prefer the PISO-1500 record to date our cores. Two excursions are preserved in our PSV records—Excursions 8α and 9α. Our revised age estimates for both excursions are 8α (236.7–239.8 ka) and 9α (283.7–286.9 ka). We have compared shipboard measurements of the two excursions with u-channel measurements of selected excursion intervals. Excursion 8α is interpreted as a ‘Class II’ excursion (local reversal) with in-phase inclination and declination changes; Excursion 9α is a ‘Class I’ excursion with 90° out-of-phase inclination and declination changes. Averaged directions (after removal of true excursional directions) and relative palaeointensity in 3 and 9 ka overlapping intervals show significant PSV directional variability over 104 yr timescales that is regionally correlatable among the four sites. A notable pattern of angular dispersion variability involves most time spent with low (∼10°) dispersion, with three shorter intervals of high (∼25°) dispersion. The relative palaeointensity variability also shows significant variability over 104 yr timescales with three notable intervals of low palaeointensity in all four records and a direct correspondence between the three low-palaeointensity intervals and the three intervals of high angular dispersion. The two magnetic field excursions occur in two of the three low-palaeointensity/high-dispersion intervals. This suggests that the geomagnetic field operates in two states between reversals, one with regular to high palaeointensity and low directional variability and one with low palaeointensity and significantly higher directional variability and excursions. |
format |
Article in Journal/Newspaper |
author |
Lund, Steve Acton, Gary Clement, Brad Okada, Makoto Keigwin, Lloyd |
author_facet |
Lund, Steve Acton, Gary Clement, Brad Okada, Makoto Keigwin, Lloyd |
author_sort |
Lund, Steve |
title |
On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
title_short |
On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
title_full |
On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
title_fullStr |
On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
title_full_unstemmed |
On the relationship between palaeomagnetic secular variation and excursions—records from MIS 8–ODP Leg 172 |
title_sort |
on the relationship between palaeomagnetic secular variation and excursions—records from mis 8–odp leg 172 |
publisher |
Oxford University Press (OUP) |
publishDate |
2020 |
url |
http://dx.doi.org/10.1093/gji/ggaa564 http://academic.oup.com/gji/advance-article-pdf/doi/10.1093/gji/ggaa564/34460930/ggaa564.pdf http://academic.oup.com/gji/article-pdf/225/2/1129/36563841/ggaa564.pdf |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Geophysical Journal International volume 225, issue 2, page 1129-1141 ISSN 0956-540X 1365-246X |
op_rights |
https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model |
op_doi |
https://doi.org/10.1093/gji/ggaa564 |
container_title |
Geophysical Journal International |
container_volume |
225 |
container_issue |
2 |
container_start_page |
1129 |
op_container_end_page |
1141 |
_version_ |
1766136637742383104 |