Comment on “New Late Pennsylvanian Paleomagnetic Results From Paraná Basin (Southern Brazil): Is the Recent Giant Gaussian Process Model Valid for the Kiaman Superchron?” by Brandt et al.

Bilardello, Dario

doi:10.1029/2019jb018556

Cited by 3 publications

(2 citation statements)

References 46 publications

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“…Key information on the reliability of a paleomagnetic pole may be better determined using data distributions. For instance, the common problem of inclination shallowing (e.g., Tauxe & Kent, 2004), as well as suspected remagnetization may be identified from a non‐Fisherian, elongated distribution of VGPs (e.g., Beck, 1999; Bilardello, 2020; Bilardello et al., 2018; Schmidt, 1990). Accurate determination of the shape of such data distributions requires large datasets (e.g., >100 sites; Tauxe et al., 2003; Tauxe & Kent, 2004; Vaes et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

Influence of Data Filters on the Position and Precision of Paleomagnetic Poles: What Is the Optimal Sampling Strategy?

Gerritsen

Vaes

Hinsbergen

2022

Geochem Geophys Geosyst

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Paleomagnetic poles, or paleopoles, quantify the past position of rocks relative to the geomagnetic pole and constrain tectonic reconstructions and apparent polar wander paths (APWPs; e.g., Besse & Courtillot, 2002;Torsvik et al., 2012). The calculation of paleopoles relies on the assumption that the time-averaged geomagnetic field approximates a geocentric axial dipole (GAD), but is complicated by short-term deviations from this field (e.g., Cromwell et al., 2018; Oliveira et al., 2021) known as paleosecular variation (PSV). To obtain a paleopole, paleomagnetists therefore average virtual geomagnetic poles (VGPs), whereby every VGP is then assumed a "spot reading": an instantaneous reading of the past geomagnetic field collected from a rock unit ("site") that represents an increment of geological time, such as a lava flow (Butler, 1992;Tauxe et al., 2010). However, not every VGP represents an accurate spot reading because artifacts may be introduced by measuring errors or remagnetization (e.g., Bilardello et al., 2018;Butler, 1992;Irving, 1961Irving, , 1964. Therefore, the paleomagnetic community commonly uses a set of data filters to acquire a set of reliable spot readings and to objectively eliminate outliers and unreliable data. However, these filters vary between authors and were not determined by studies aiming to constrain paleopoles.The studies that established the data filters, investigated PSV and geomagnetic field behavior by determining the between-site scatter of a set of VGPs (e.g.,

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Section: Discussionmentioning

confidence: 99%

Influence of Data Filters on the Position and Precision of Paleomagnetic Poles: What Is the Optimal Sampling Strategy?

Gerritsen

Vaes

Hinsbergen

2022

Geochem Geophys Geosyst

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“…Key information on the reliability of a paleomagnetic pole may be better determined using data distributions. For instance, the common problem of inclination shallowing (e.g., , as well as suspected remagnetization may be identified from a non-Fisherian, elongated distribution of VGPs (e.g., Beck, 1999;Bilardello, 2020;Bilardello et al, 2018;Schmidt, 1990). Accurate determination of the shape of such data distributions requires large datasets (e.g., >100 sites; Tauxe et al, 2003;Chapter 3).…”

Section: Discussionmentioning

confidence: 99%

On pole position

Vaes¹

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Paleomagnetism provides the only quantitative tool to reconstruct the position and motion of tectonic plates and continents in deep geological time. These reconstructions often rely on apparent polar wander paths (APWPs), which describe the past position and motion of plates relative to the Earth’s spin axis. In addition to providing a paleomagnetic reference frame for paleogeography, these paths serve to quantify relative tectonic displacements with other lithospheric blocks. A long-discussed problem is that conventional approaches to computing polar wander do not propagate key sources of uncertainty in the underlying data, such as data scatter or age uncertainty, but proposed solutions remained mostly qualitative. Recently, this problem became more urgent: Rowley (2019, Tectonics) showed that as much as 50% of the data that underlie the currently most widely used global APWP are statistically significantly displaced relative to that APWP. This implies that the resolution at which a geologically meaningful statistical difference between a paleomagnetic dataset and an APWP may be determined, is strongly limited, which undermines the current tectonic and paleogeographic applications of paleomagnetism. This thesis aims to examine the causes of dispersion of paleomagnetic data behind APWPs and to build a global APWP in which key data uncertainties are propagated, such that it may be used to determine geologically meaningful relative displacements. We show that the uncertainty of APWPs computed from paleomagnetic poles, which is the current standard, is mostly determined by the arbitrary choice of how many datapoints are used per pole. This thesis then develops a novel approach in which apparent polar wander paths are computed from site-level paleomagnetic data instead of paleomagnetic poles. In this approach, larger weight is assigned to larger datasets and temporal and spatial uncertainties in the paleomagnetic data are incorporated. We present a global apparent polar wander path for the last 320 Ma using the new statistical approach proposed in this thesis, as well as using a fully updated paleomagnetic database. We find that the first-order geometry of this path is similar to previous models but with smaller uncertainties. Moreover, we show that correcting for temporal bias in the paleomagnetic data allows improved quantification of polar wander rates, and that previously observed peaks in polar wander likely resulted from such bias. We introduce the open-source web application APWP-online.org that provides user-friendly tools to compute apparent polar wander paths using our new methodology as well as the computation of relative paleomagnetic displacements. The website also hosts a community platform for the continuous improvement of the path in the future through the addition of new high-quality paleomagnetic data. Finally, we provide new quantitative estimates of true polar wander during the last 320 Ma by comparing our new global apparent polar wander path with existing mantle reference frames. The computed true polar wander paths suggest that the true polar wander rotations occurred about two roughly orthogonal axes in the equatorial plane. We discuss the geodynamic implications of these findings and highlight future opportunities for the identification and quantification of true polar wander on geological timescales.

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Middle–Late Permian magnetostratigraphy and the onset of the Illawarra Reversals in the northeastern Parana Basin, South America

Aragão

Scardia

2021

Geophysical Journal International

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Summary Recent compilations of the Illawarra Reversals show remarkable differences in the onset age (265 vs 269 Ma) and the magnetic polarity pattern, hampering the establishment of a reference geomagnetic timescale for the Middle–Late Permian. The Parana Basin hosts a 7 km-thick, discontinuous sedimentary succession spanning the Paleozoic to the Mesozoic, including the Gondwana 1 super-sequence which extends from Late Carboniferous to the Triassic or Jurassic. We provide the magnetostratigraphy of the middle and upper Permian part of this sequence of a ca. 300 m-long core, pertaining to the Passa Dois Group and the Piramboia Formation. Sample demagnetization of NRM revealed two magnetic overprints ascribed to the Brunhes chron and to the emplacement of Parana Large Igneous Province in the Early Cretaceous, respectively. Stable, dual polarity characteristic components (ChRM) were isolated at temperatures higher than 450 °C and interpreted as a primary detrital magnetic remanence (DRM), acquired during or soon after sediment deposition. Available U-Pb dating on volcanic zircons from the literature provided independent chronologic constraints for our magnetostratigraphy. A total of 8 reverse polarity intervals were identified, the lowermost of which (up to 110 m-thick) correlates to the Kiaman Superchron. The overlying Illawarra is dominated by a reverse polarity magnetization with thin (4–5 m-thick) normal polarity intervals. This pattern agrees with the Illawarra sequence from the Karoo Basin and other proposed timescales for the Permian. The onset of the Illawarra reversals is interpolated to ca. 270 Ma, close to the age of 269 Ma from the Karoo Basin. Combined magnetostratigraphy and geochronology yielded sediment accumulation rates of ca. 8 m/Myr for the Passa Dois Group in the northeastern (marginal) sector of the Parana Basin, indicating that Serra Alta and Teresina Formations span 279 to 274 Ma and 274 to 254 Ma, respectively.

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Comment on “New Late Pennsylvanian Paleomagnetic Results From Paraná Basin (Southern Brazil): Is the Recent Giant Gaussian Process Model Valid for the Kiaman Superchron?” by Brandt et al.

Cited by 3 publications

References 46 publications

Influence of Data Filters on the Position and Precision of Paleomagnetic Poles: What Is the Optimal Sampling Strategy?

Influence of Data Filters on the Position and Precision of Paleomagnetic Poles: What Is the Optimal Sampling Strategy?

On pole position

Middle–Late Permian magnetostratigraphy and the onset of the Illawarra Reversals in the northeastern Parana Basin, South America

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