Abstract
The youngest geomagnetic polarity reversal, the Matuyama–Brunhes (M–B) boundary, provides an important plane of data for sediments, ice cores, and lavas. The geomagnetic field intensity and directional changes that occurred during the reversal also provide important information for understanding the dynamics of the Earth’s outer core, which generates the magnetic field. However, the reversal process is relatively rapid in terms of the geological timescale; therefore, adequate temporal resolution of the geomagnetic field record is essential for addressing these topics. Here, we report a new high-resolution paleomagnetic record from a continuous marine succession in the Chiba composite section of the Kokumoto Formation of the Kazusa Group, Japan, that reveals detailed behaviors of the virtual geomagnetic poles (VGPs) and relative paleointensity changes during the M–B polarity transition. The resultant relative paleointensity and VGP records show a significant paleointensity minimum near the M–B boundary, which is accompanied by a clear “polarity switch.” A newly obtained high-resolution oxygen isotope chronology for the Chiba composite section indicates that the M–B boundary is located in the middle of marine isotope stage (MIS) 19 and yields an age of 771.7 ka for the boundary. This age is consistent with those based on the latest astronomically tuned marine and ice core records and with the recalculated age of 770.9 ± 7.3 ka deduced from the U–Pb zircon age of the Byk-E tephra. To the best of our knowledge, our new paleomagnetic data represent one of the most detailed records on this geomagnetic field reversal that has thus far been obtained from marine sediments and will therefore be key for understanding the dynamics of the geomagnetic dynamo and for calibrating the geological timescale.Graphical abstract.
Highlights
The Earth’s latest magnetic field reversal event, the Matuyama–Brunhes (M–B) boundary, is an important calibration point on the geological timescale, connecting sediments and volcanic rocks, and has been the focus of a number of paleomagnetic studies
Rock‐magnetic characteristics Hysteresis loops of the representative specimens exhibit no evidence of wasp-waisted characteristics (Fig. 3a), indicating there are no obvious contributions from superparamagnetic grains or high-coercivity magnetic minerals (Roberts et al 1995; Tauxe et al 1996)
The hysteresis data fall within a limited range of magnetic grain sizes that correspond to pseudo-single-domain (PSD) sizes (Fig. 3b)
Summary
The Earth’s latest magnetic field reversal event, the Matuyama–Brunhes (M–B) boundary, is an important calibration point on the geological timescale, connecting sediments and volcanic rocks, and has been the focus of a number of paleomagnetic studies. Okada et al Earth, Planets and Space (2017) 69:45 in the geomagnetic field intensity and the 10Be production rate in the atmosphere provide a timescale that has been widely used in the geochronology of marine sediments (e.g., Guyodo and Valet 1999; Yamazaki 1999; Channell and Kleiven 2000; Laj et al 2000; Stoner et al 2000; Kiefer et al 2001; Christl et al 2003, 2007; Horng et al 2003; Valet et al 2005, 2014; Yamazaki and Oda 2005; Yamamoto et al 2007; Yamazaki and Kanamatsu 2007; Suganuma et al 2008; Channell et al 2008, 2009, 2010, 2014, 2016; Inoue and Yamazaki 2010: Macri et al 2010; Mazaud et al 2012, 2015) These geomagnetic field intensity data associated with the directional change contain essential information about the Earth’s magnetic field reversal; the nature of the geomagnetic dynamo in the Earth’s outer core remains a controversial topic (e.g., Valet and Fournier 2016). This U–Pb zircon age, coupled with an astronomical age for the marine sediment, yields an M–B boundary age of
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