| Autor: |
Borlina, Cauê S., Lima, Eduardo A., Feinberg, Joshua M., Jaqueto, Plinio, Lascu, Ioan, Trindade, Ricardo I. F., Font, Eric, Sánchez‐Moreno, Elisa M., Dimuccio, Luca Antonio, Yokoyama, Yusuke, Parés, Josep M., Weiss, Benjamin P., Dorale, Jeffrey A. |
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| Zdroj: |
Geochemistry, Geophysics, Geosystems: G3; Oct2024, Vol. 25 Issue 10, p1-20, 20p |
| Abstrakt: |
Speleothems are mineral deposits capable of recording detrital and/or chemical remanent magnetization at annual timescales. They can offer high‐resolution paleomagnetic records of short‐term variations in Earth's magnetic field, crucial for understanding the evolution of the dynamo. Owing to limitations on the magnetic moment sensitivity of commercial cryogenic rock magnetometers (∼10−11 Am2), paleomagnetic studies of speleothems have been limited to samples with volumes of several hundreds of mm3, averaging tens to hundreds of years of magnetic variation. Nonetheless, smaller samples (∼1–10 mm3) can be measured using superconducting quantum interference device (SQUID) microscopy, with a sensitivity better than ∼10−15 Am2. To determine the application of SQUID microscopy for obtaining robust high‐resolution records from small‐volume speleothem samples, we analyzed three different stalagmites collected from Lapa dos Morcegos Cave (Portugal), Pau d'Alho Cave (Brazil), and Crevice Cave (United States). These stalagmites are representative of a range of magnetic properties and have been previously studied with conventional rock magnetometers. We show that by using SQUID microscopy we can achieve a five‐fold improvement in temporal resolution for samples with higher abundances of magnetic carriers (e.g., Pau d'Alho Cave and Lapa dos Morcegos Cave). In contrast, speleothems with low abundances of magnetic carriers (e.g., Crevice Cave) do not benefit from higher resolution analysis and are best analyzed using conventional rock magnetometers. Overall, by targeting speleothem samples with high concentrations of magnetic carriers we can increase the temporal resolution of magnetic records, setting the stage for resolving geomagnetic variations at short time scales. Plain Language Summary: Earth has a magnetic field that is generated in the outer core, and through paleomagnetism we can retrieve information about the evolution of the field from rocks. Different types of rocks have been used to determine how Earth's magnetic field has changed over time. In this study, we use magnetic microscopy to analyze the magnetic record of speleothems, which are rocks that form inside caves and that can record magnetic fields in annual scales. This allows us to obtain magnetic records with higher resolution than previous studies. This is important because Earth's magnetic field changes in timescales ranging from thousands of years to a few years, and obtaining records from speleothems using magnetic microscopy can help us track these variations. We provide data demonstrating how the technique can be used and showing its limitations, and we discuss how the geologic context of the cave influences the robustness of the magnetic record. We also provide protocols for future studies using magnetic microscopy in speleothems. Key Points: Magnetic microscopy can be used to produce a 5× improvement in temporal resolution of magnetic records from speleothemsVariations in magnetic properties across speleothems can affect the temporal resolution of the magnetic recordProtocols for conducting high‐resolution magnetic measurements of speleothems with magnetic microscopy are presented [ABSTRACT FROM AUTHOR] |
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