Downward remagnetization of a ∼74-m-thick zone in lake sediments from palaeo-Lake Idaho (NW United States): locating the Gauss/Matuyama geomagnetic boundary within a dual-polarity zone
SUMMARY. Remagnetization is an important issue in palaeomagnetism. Here, we discuss an extraordinarily thick (∼74 m) dual-polarity transition zone between the Gauss and Matuyama Chrons. The studied succession is from a drill core through lacustrine sediments of palaeo-Lake Idaho (Snake River Plain,...
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| Main Authors: | , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
29 April 2020
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| In: |
Geophysical journal international
Year: 2020, Volume: 222, Issue: 2, Pages: 754-768 |
| ISSN: | 1365-246X |
| DOI: | 10.1093/gji/ggaa165 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1093/gji/ggaa165 Verlag, lizenzpflichtig, Volltext: https://academic.oup.com/gji/article/222/2/754/5826815 
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| Author Notes: | Frederik J. Allstädt, Erwin Appel, Wolfgang Rösler, Alexander A. Prokopenko, Udo Neumann, Thomas Wenzel, Jörg Pross |
| Summary: | SUMMARY. Remagnetization is an important issue in palaeomagnetism. Here, we discuss an extraordinarily thick (∼74 m) dual-polarity transition zone between the Gauss and Matuyama Chrons. The studied succession is from a drill core through lacustrine sediments of palaeo-Lake Idaho (Snake River Plain, NW United States of America) that are intercalated with basalt units. We identified detrital Ti-rich titanomagnetite and magnetite in lamellar exsolutions as the main carriers of a primary remanence, likely derived from the basalts that erupted in the Snake River Plain. Stepwise thermal demagnetization revealed a single-component remanent magnetization with reversed and normal polarities above and below the transition zone, respectively. Based on rock-magnetic results, microscopic observations, and previously known events in the evolution of palaeo-Lake Idaho, the reversed-polarity component in the transition zone represents a secondary chemical remanent magnetization caused by magnetic mineral alteration or partial neo-formation of magnetite, in association with strong depletion of the primary detrital magnetic minerals that affected a wide depth range below the level where the remagnetization event occurred. This remagnetization event was most likely related to lake-level lowering and partial desiccation of palaeo-Lake Idaho. Understanding the nature and origin of the remagnetization allows to identify the polarity boundary in the unusual case of a secondary magnetization with reversed polarity produced downward in a sequence to an extraordinary large depth. Based on available age information, the observed reversal represents the Gauss/Matuyama boundary, which provides an important age constraint for palaeoclimatic interpretation of the succession |
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| Item Description: | Gesehen am 26.10.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1365-246X |
| DOI: | 10.1093/gji/ggaa165 |