Downward remagnetization of a ∼74-m-thick zone in lake sediments from palaeo-Lake Idaho (NW United States)

• Verfasst von: Allstädt, Frederik J. [VerfasserIn]
• Verfasst von: Appel, Erwin [VerfasserIn]
• Verfasst von: Rösler, Wolfgang [VerfasserIn]
• Verfasst von: Prokopenko, Alexander A. [VerfasserIn]
• Verfasst von: Neumann, Udo [VerfasserIn]
• Verfasst von: Wenzel, Thomas [VerfasserIn]
• Verfasst von: Pross, Jörg [VerfasserIn]
• Titel: Downward remagnetization of a ∼74-m-thick zone in lake sediments from palaeo-Lake Idaho (NW United States)
• Titelzusatz: locating the Gauss/Matuyama geomagnetic boundary within a dual-polarity zone
• Verf.angabe: Frederik J. Allstädt, Erwin Appel, Wolfgang Rösler, Alexander A. Prokopenko, Udo Neumann, Thomas Wenzel, Jörg Pross
• E-Jahr: 2020
• Jahr: 29 April 2020
• Umfang: 15 S.
• Fussnoten: Gesehen am 26.10.2020
• Titel Quelle: Enthalten in: Geophysical journal international
• Ort Quelle: Oxford : Oxford Univ. Press, 1958
• Jahr Quelle: 2020
• Band/Heft Quelle: 222(2020), 2, Seite 754-768
• ISSN Quelle: 1365-246X
• DOI: doi:10.1093/gji/ggaa165
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1736589792

Abstract

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