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Title

Geomagnetic, cosmogenic and climatic changes across the last geomagnetic reversal from Equatorial Indian Ocean sediments

Publication Year

2014

Author(s)
  • Valet, Jean-Pierre
  • Bassinot, Franck
  • Bouilloux, Alexandra
  • Bourles, Didier
  • Nomade, Sebastien
  • Guillou, Valery
  • Lopes, Fernand
  • Thouveny, Nicolas
  • Dewilde, Fabien
Source
EARTH AND PLANETARY SCIENCE LETTERS Volume: 397 Pages: 67-79 Published: 2014
ISSN
0012-821X eISSN: 1385-013X
Abstract

High-resolution records of beryllium (Be-10) production and relative paleointensity have been obtained across the Matuyama-Brunhes (M-B) reversal from the equatorial Indian Ocean (Maldives area). Both magnetic and geochemical analyses were performed from the same discrete samples to avoid any artificial depth offset. The authigenic Be-10 concentrations were normalized with respect to Be-9 in order to correct for potential environmental effects, while the relative paleointensity was derived from the remanent magnetization intensity after accounting for changes in magnetic concentration within the sediment. The relative paleointensity and the Be-10/Be-9 records are both characterized by large deviations, which culminate in the middle of the reversal. In contrast to most previous studies, and despite relative high deposition rate (4.7 cm/ka), we observed a perfect synchronism between the Be-10/Be-9 peak, the lowest value of relative paleointensity and the switch in direction, which indicates that bioturbation and post-depositional processes did not affect the magnetic record. This leaves no ambiguity for the stratigraphic position of the reversal located within Marine Isotopic Stage 19 as revealed by the planktonic delta O-18 record from the same core. The magnetic data depict a two-phase process with a precursory event preceding the rapid polarity switch, while only the second phase is present in the Be-10 record, similarly to other low latitude records from the Indonesian area. Using an orbitally-tuned age model, we obtain an age of 772 ka +/- 5 ka for the middle of the transition, while the precursory event occurred almost 20 ka before. We believe that the bimodal distribution emerging from the compilations of the ages of the M-B reversal results from the succession of these two events. Microtektites from the Australasian impact were found at 0.6 m below the transition (790 ka +/- 5 ka B.P.) and confirm that this large event occurred 12 ka prior to the polarity transition. The distribution of tektite abundance was used to deconvolve the Be-10/Be-9 signal. The results confirm that the beryllium changes are concentrated during the transitional period, thus likely in presence of a multipolar geomagnetic field (or in the vicinity of a geomagnetic pole) that favored the penetration of cosmic rays and consequently increased the Be-10 production. The absence of Be-10 during the precursor indicates that the present site and the Indonesian ones were far away from a geomagnetic pole and that interlatitudinal atmospheric mixing was limited. The geomagnetic pole positions above the Indonesian sites during the precursor would thus be incompatible with the corresponding inclined dipolar field during this period, and suggest the dominance of low-degree harmonics. (C) 2014 Elsevier B.V. All rights reserved.

Author Keyword(s)
  • reversals
  • geomagnetic field
  • beryllium
  • astrochronology
  • magnetization
KeyWord(s) Plus
  • MATUYAMA-BRUNHES BOUNDARY
  • AUTHIGENIC BE-10/BE-9 SIGNATURE
  • CANYON SANIDINE STANDARD
  • K-40 DECAY CONSTANTS
  • DEEP-SEA SEDIMENTS
  • AR-40/AR-39 GEOCHRONOLOGY
  • JOINT DETERMINATION
  • EARTHS ATMOSPHERE
  • POLARITY REVERSAL
  • IMPROVED ACCURACY
ESI Discipline(s)
  • Geosciences
Web of Science Category(ies)
  • Geochemistry & Geophysics
Adress(es)

[Valet, Jean-Pierre; Bouilloux, Alexandra; Lopes, Fernand] Univ Paris Diderot, Sorbonne Paris Cite, CNRS, Inst Phys Globe Paris,UMR 7154, F-75238 Paris 05, France; [Bassinot, Franck; Nomade, Sebastien; Dewilde, Fabien] CEA, CNRS, UVSQ, Lab Sci Climat & Environm, F-91198 Gif Sur Yvette, France; [Bourles, Didier; Guillou, Valery; Thouveny, Nicolas] Aix Marseille Univ, Coll France, CNRS, IRD,UM CEREGE 34, F-13545 Aix En Provence, France

Reprint Adress

Valet, JP (reprint author), Univ Paris Diderot, Sorbonne Paris Cite, CNRS, Inst Phys Globe Paris,UMR 7154, 1 Rue Jussieu, F-75238 Paris 05, France.

Country(ies)
  • France
CNRS - Adress(es)
  • Centre européen de recherche et d'enseignement de géosciences de l'environnement (CEREGE), UMR7330
  • Institut de Physique du Globe de Paris (IPGP), UMR7154
  • Laboratoire des sciences du climat et de l'environnement (LSCE), UMR8212
Accession Number
WOS:000337554400007
uid:/087429JS
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