Paleomag

2023

1. Quantitative Analysis of Paleomagnetic Sampling Strategies

   F. Sapienza, L. C. Gallo, Y. Zhang, B. Vaes, M. Domeier, and N. L. Swanson-Hysell

   Journal of Geophysical Research: Solid Earth, 2023

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   Abstract Sampling strategies used in paleomagnetic studies play a crucial role in dictating the accuracy of our estimates of properties of the ancient geomagnetic field. However, there has been little quantitative analysis of optimal paleomagnetic sampling strategies and the community has instead defaulted to traditional practices that vary between laboratories. In this paper, we quantitatively evaluate the accuracy of alternative paleomagnetic sampling strategies through numerical experiments and an associated analytical framework. Our findings demonstrate a strong correspondence between the accuracy of an estimated paleopole position and the number of sites or independent readings of the time-varying paleomagnetic field, whereas larger numbers of in-site samples have a dwindling effect. This remains true even when a large proportion of the sample directions are spurious. This approach can be readily achieved in sedimentary sequences by distributing samples stratigraphically, considering each sample as an individual site. However, where the number of potential independent sites is inherently limited the collection of additional in-site samples can improve the accuracy of the paleopole estimate (although with diminishing returns with increasing samples per site). Where an estimate of the magnitude of paleosecular variation is sought, multiple in-site samples should be taken, but the optimal number is dependent on the expected fraction of outliers. The use of filters based on angular distance helps the accuracy of paleopole estimation, but leads to inaccurate estimates of paleosecular variation. We provide both analytical formulas and a series of interactive Jupyter notebooks allowing optimal sampling strategies to be developed from user-informed expectations.

   @article{sapienza2023quantitative,
     author = {Sapienza, F. and Gallo, L. C. and Zhang, Y. and Vaes, B. and Domeier, M. and Swanson-Hysell, N. L.},
     title = {Quantitative Analysis of Paleomagnetic Sampling Strategies},
     journal = {Journal of Geophysical Research: Solid Earth},
     volume = {128},
     number = {11},
     pages = {e2023JB027211},
     keywords = {paleomagnetism, paleopole estimation, secular variation, error quantification},
     doi = {https://doi.org/10.1029/2023JB027211},
     url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023JB027211},
     eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023JB027211},
     year = {2023},
   }

2. Embracing Uncertainty to Resolve Polar Wander: A Case Study of Cenozoic North America

   L. C. Gallo, M. Domeier, F. Sapienza, N. L. Swanson-Hysell, B. Vaes, Y. Zhang, M. Arnould, A. Eyster, D. Gürer, Á. Király, B. Robert, T. Rolf, and 2 more authors

   Geophysical Research Letters, 2023

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   Abstract Our understanding of Earth’s paleogeography relies heavily on paleomagnetic apparent polar wander paths (APWPs), which represent the time-dependent position of Earth’s spin axis relative to a given block of lithosphere. However, conventional approaches to APWP construction have significant limitations. First, the paleomagnetic record contains substantial noise that is not integrated into APWPs. Second, parametric assumptions are adopted to represent spatial and temporal uncertainties even where the underlying data do not conform to the assumed distributions. The consequences of these limitations remain largely unknown. Here, we address these challenges with a bottom-up Monte Carlo uncertainty propagation scheme that operates on site-level paleomagnetic data. To demonstrate our methodology, we present an extensive compilation of site-level Cenozoic paleomagnetic data from North America, which we use to generate a high-resolution APWP. Our results demonstrate that even in the presence of substantial noise, polar wandering can be assessed with unprecedented temporal and spatial resolution.

   @article{gallo2023embracing,
     author = {Gallo, L. C. and Domeier, M. and Sapienza, F. and Swanson-Hysell, N. L. and Vaes, B. and Zhang, Y. and Arnould, M. and Eyster, A. and Gürer, D. and Király, Á. and Robert, B. and Rolf, T. and Shephard, G. and van der Boon, A.},
     title = {Embracing Uncertainty to Resolve Polar Wander: A Case Study of Cenozoic North America},
     journal = {Geophysical Research Letters},
     volume = {50},
     number = {11},
     pages = {e2023GL103436},
     keywords = {paleomagnetism, polar wander, uncertainty quantification},
     doi = {https://doi.org/10.1029/2023GL103436},
     eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023GL103436},
     year = {2023},
   }

2022

1. An optimization method for paleomagnetic Euler pole analysis

   Leandro C Gallo, Facundo Sapienza, and Mathew Domeier

   Computers & Geosciences, 2022

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   Owing to the axial symmetry of the Earth’s magnetic field, paleomagnetic data only directly record the latitudinal and azimuthal positions of crustal blocks in the past, and paleolongitude cannot be constrained. An ability to overcome this obstacle is thus of fundamental importance to paleogeographic reconstruction. Paleomagnetic Euler pole (PEP) analysis presents a unique means to recover such information, but prior implementations of the PEP method have incorporated subjective decisions into its execution, undercutting its fidelity and rigor. Here we present an optimization approach to PEP analysis that addresses some of these deficiencies—namely the objective identification of change-points and small-circle arcs that together approximate an apparent polar wander path. We elaborate on our novel methodology and conduct some experiments with synthetic data to demonstrate its performance. We furthermore present implementations of our methods both as adaptable, stand-alone scripts in Python and as a streamlined interactive workflow that can be operated through a web browser.

   @article{gallo2022optimization,
     title = {An optimization method for paleomagnetic Euler pole analysis},
     author = {Gallo, Leandro C and Sapienza, Facundo and Domeier, Mathew},
     journal = {Computers \& Geosciences},
     volume = {166},
     pages = {105150},
     year = {2022},
     publisher = {Elsevier},
   }

2018

1. Anhysteretic remanent magnetization: model of grain size distribution of spherical magnetite grains

   Carlos A Vasquez, Facundo Sapienza, Agustı́n Somacal, and Sabrina Y Fazzito

   Studia Geophysica et Geodaetica, 2018

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   A phenomenological model based on a linear relationship between the magnetic coercivity field and the reciprocal of the grain diameter is applied to explain the anhysteretic remanent magnetization (ARM) imparted to artificial samples with different concentrations of a very well characterized magnetite powder. By analyses of scanning electron microscopy images, the spherically shaped single domain synthetic magnetite is found to follow a lognormal grain size distribution with  86 nm of mean diameter. The proposed model, fitted to ARM measurements up to a peak alternating field of 100 mT, yields a very good agreement. The coercivity behaviour predicted by micromagnetism theory disagrees with the experimental results of this work. A likely explanation for the discrepancy is that the magnetite particles, which consist of a mixture of grains in coherent rotation and curling modes, produce similar observations as domain processes.

   @article{vasquez2018anhysteretic,
     title = {Anhysteretic remanent magnetization: model of grain size distribution of spherical magnetite grains},
     author = {Vasquez, Carlos A and Sapienza, Facundo and Somacal, Agust{\'\i}n and Fazzito, Sabrina Y},
     journal = {Studia Geophysica et Geodaetica},
     volume = {62},
     pages = {339--351},
     year = {2018},
     publisher = {Springer},
   }