A Quaternary geomagnetic instability time scale |
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| Affiliation: | 1. Department of Geological Sciences, POB 112120, University of Florida, Gainesville, FL 32611, USA;2. Laboratoire des Sciences du Climat et de l''Environnement, LSCE/IPSL, CNRS-CEA-UVSQ, Université de Paris-Saclay, F-91198 Gif-sur-Yvette, France;3. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK;4. Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland;1. Faculty of Archaeology, Leiden University, P.O. Box 9515, 2300 RA Leiden, The Netherlands;2. Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Paseo Sierra de Atapuerca 3, 09002 Burgos, Spain;3. Paleomagnetic Laboratory ‘Fort Hoofddijk’, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands;4. Laboratoire de Geographie Physique, UMR 8591 CNRS, 1 Place Aristide Briand, F-92195 Meudon Cedex, France;5. INRAP, 518 rue Saint-Fuscien, F-80000 Amiens, France;1. Department of Anthropology, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada;2. Department of Anthropology, University of Wisconsin-Madison, 1180 Observatory Drive, Madison, WI, 53706, USA;3. Evolutionary Studies Institute, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa;4. Plio-Pleistocene Palaeontology Section, Department of Vertebrates, Ditsong National Museum of Natural History (Transvaal Museum), Pretoria, 0002, South Africa;5. School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa;6. Department of Biology, Birmingham-Southern College, Birmingham, AL, 35254, USA;7. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, USA;1. Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris-Cité, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France;2. Laboratoire des Sciences du Climat et de l''Environnement (CEA-CNRS-UVSQ), Domaine du CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France;3. Aix-Marseille Université, CNRS-IRD-Collège de France, UM 34 CEREGE, Technopôle de l''Environnement Arbois-Méditerranée, BP80, 13545 Aix-en-Provence, France;1. CEREGE UM34, Aix Marseille Univ., CNRS, IRD, INRA, Coll France, Aix-en-Provence, France;2. Institut de Physique du Globe de Paris, Sorbonne Paris-Cité, Université Paris Diderot, UMR 7154 CNRS, Paris, France;3. LSCE, UMR8212, LSCE/IPSL, CEA–CNRS–UVSQ and Université Paris-Saclay, Gif-Sur-Yvette, France;1. Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris-Cité, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France;2. Laboratoire des Sciences du Climat et de l''Environnement (CEA-CNRS-UVSQ), Domaine du CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France;3. CEREGE UM34, Aix Marseille Univ., CNRS, IRD, INRA, Coll France, Aix-en-Provence, France |
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| Abstract: | Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states in lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which oxygen isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments gives rise to a GITS that comprises 10 polarity reversals and 27 excursions that occurred during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Gauss-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented geomagnetic field instabilities manifest as short-lived excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron. Nineteen excursions have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and these form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. |
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