Paleointensity of the geomagnetic field in the Late Cretaceous and earliest Paleogene obtained from drill cores of the Louisville seamount trail

Torii

Natsuhara³

2015

Earth Planet Sp

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In 1972, a reconstruction experiment of a kiln had been done to reproduce an excavated kiln of the seventh century in Japan. Baked clay samples were taken from the floor surface and −20 cm level, and they have been stored after determinations of the paleomagnetic directions by partial alternating field demagnetizations. We recently applied the Tsunakawa-Shaw method to the samples to assess how reliable archeointensity results are obtained from the samples. A suite of the rock magnetic experiments and the scanning electron microscope observations elucidate that dominant magnetic carriers of the floor surface samples are Ti-poor titanomagnetite grains in approximately 10 nm size with single-domain and/or super-paramagnetic states, whereas contributions of multi-domain grains seem to be relatively large for the −20-cm level samples. From the floor surface samples, six out of the eight successful results were obtained and they give an average of 47.3 μT with a standard deviation of 2.2 μT. This is fairly consistent with the in situ geomagnetic field of 46.4 μT at the time of the reconstruction. They are obtained with a built-in anisotropy correction using anhysteretic remanent magnetization and without any cooling rate corrections. In contrast, only one out of four was successful from the −20-cm level samples. It yields an archeointensity of 31.6 μT, which is inconsistent with the in situ geomagnetic field. Considering from the in situ temperature record during the firing of the kiln and the unblocking temperature spectra of the samples, the floor surface samples acquired full thermoremanent magnetizations (TRMs) as their natural remanent magnetizations whereas the −20-cm level samples only acquired partial TRMs, and these differences probably cause the difference in the archeointensity results between the two sample groups. For archeointensity researches, baked clay samples from a kiln floor are considered to be ideal materials.

Section: Tsunakawa-shaw Paleointensity Experimentsmentioning

confidence: 99%

Archeointensity study on baked clay samples taken from the reconstructed ancient kiln: implication for validity of the Tsunakawa-Shaw paleointensity method

Torii

Natsuhara³

2015

Earth Planet Sp

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“…Alternatively, the low VDM average might be due to that the stratigraphic positions of their data are fairly close to polarity boundaries. Our averaged VADM is similar to the previously reported V(A)DM averages estimated using the Tsunakawa‐Shaw method: the averaged VDM of 3.6 ± 2.1 × 10 22 Am 2 for the interval of 0.5–4.6 Ma (Yamamoto & Tsunakawa, 2005), the averaged VADM of 3.7 ± 1.9 × 10 22 Am 2 for the interval of 1.96–2.34 Ma (Ahn et al., 2016), the averaged VADM of 3.4 ± 1.2 for Chron C27r, 3.6 ± 1.3 for Chron C31n, and 3.8 ± 1.6 × 10 22 Am 2 for Chron C32n.2n (recalculated from Yamazaki & Yamamoto, 2014 and revised chron assignments based on the new age model of Heaton & Koppers, 2019). The coincidence of the paleointensity values from the Tsunakawa‐Shaw method for a long time span implies that a V(A)DM of ∼4 × 10 22 Am 2 may be regarded as a long‐term average.…”

Section: Discussionmentioning

confidence: 99%

“…Information on the history of Earth's magnetic field is essential for understanding the geodynamo evolution, and variations in the intensity of the geomagnetic field in the past (paleointensity) are fundamentally important for constraining numerical geodynamo models. Despite a long history of research, there is still controversy about the long‐term trend of time‐averaged virtual (axial) dipole moment (V(A)DM): for example, the possibility of a stronger paleointensity during the Cretaceous Normal Superchron (Qin et al., 2011; P. Riisager et al., 2003; Tanaka & Kono, 2002; Tarduno et al., 2001, 2002; Tauxe & Staudigel, 2004; Tsunakawa et al., 2009; Zhu et al., 2008) and a relationship between paleointensity and the geomagnetic reversal frequency (Kulakov et al., 2019; Sprain et al., 2016; Tarduno & Cottrell, 2005; Tauxe et al., 2013; Yamazaki & Yamamoto, 2014). We consider that the discrepancy may be due to the difficulty in estimating representative V(A)DMs.…”

Section: Introductionmentioning

confidence: 99%

“…Tauxe and Staudigel (2004) proposed a minimum required flow number of 25 to estimate a robust VADM average using a Monte Carlo simulation based on the TK03 geomagnetic field model (Tauxe & Kent, 2004). However, only five studies have obtained time‐averaged V(A)DMs from 15 or more flows for the last 160 Myr (Granot et al., 2007; Selkin & Tauxe, 2000; Tauxe & Staudigel, 2004; Yamamoto & Tsunakawa, 2005; Yamazaki & Yamamoto, 2014). Second, there is a possibility that the paleointensity distribution is not Gaussian but skewed to lower intensities (e.g., McFadden & McElhinny, 1982; Tanaka et al., 1995).…”

Section: Introductionmentioning

confidence: 99%

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Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Yoshimura

Yamazaki

Geochem Geophys Geosyst

et al. 2020

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Information on the history of Earth's magnetic field is essential for understanding the geodynamo evolution, and variations in the intensity of the geomagnetic field in the past (paleointensity) are fundamentally important for constraining numerical geodynamo models. Despite a long history of research, there is still controversy about the long-term trend of time-averaged virtual (axial) dipole moment (V(A)DM): for example, the possibility of a stronger paleointensity during the Cretaceous Normal Superchron (

“…Paleointensity was estimated from the linear segment of the NRM-TRM1 * diagram when the ARM correction was judged to be valid based on the linear segment of the TRM1-TRM2 * diagram. We adopted the following selection criteria, which are similar to those used with the Tsunakawa-Shaw method in recent paleointensity studies (e.g., Yamamoto et al, 2010Yamamoto et al, , 2015Yamazaki and Yamamoto, 2014): Rubin et al (1987);…”

Section: Tsunakawa-shaw Paleointensity Experimentsmentioning

confidence: 99%

Paleointensity Study on the Holocene Surface Lavas on the Island of Hawaii Using the Tsunakawa–Shaw Method

Ryo

2018

Front. Earth Sci.

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Investigating volcanic paleointensity during the Holocene is important for linking archeointensity and sedimentary paleointensity. Across the globe, the island of Hawaii is one of the most studied subaerial locations. Many published data from Hawaii are accessible in the paleointensity databases, but it is necessary to reassess these data because they were determined with experimental protocols not incorporating a modern test for multi-domain particles and with relatively loose selection criteria. To obtain a new paleointensity dataset based on coercivity spectra rather than blocking temperature spectra, we applied the Tsunakawa-Shaw method to Holocene surface lavas collected from 34 sites on the island of Hawaii. In total, 135 successful results were obtained after applying the specimen-level selection criteria, yielding 22 site-mean Tsunakawa-Shaw paleointensities (TS dataset) that fulfilled the site-level selection criteria. We compared the TS dataset with the IZZI dataset, which includes recently reported blocking-temperature-based paleointensities determined by the IZZI Thellier method with the stringent criteria CCRIT. The cumulative distribution function (CDF) curve of the TS dataset, except for three sites, almost overlaps that of the IZZI dataset, and the medians coincide with each other, 42.9 µT (N = 19) for the TS dataset and 43.5 µT (N = 28) for the IZZI dataset. The coincidence of the CDF curves suggests equivalent reliability of the Tsunakawa-Shaw method and the IZZI Thellier method. The Holocene paleointensity variation in Hawaii is thought to be reliably characterized by both the TS dataset and the IZZI dataset: overall, the paleointensity throughout the Holocene is suggested to be higher than the present-day field. It is also inferred that there are possible decadal-and centennial-timescale large-intensity variations between ∼1,800 and ∼2,000 cal BP, and between ∼3,000 and ∼3,500 cal BP. The latter variation might be inferred as a global-scale dipolar phenomenon, as consistent paleointensity results are reported from archaeological sources in the Levant by the IZZI Thellier method.