Reliable identification of flood-borne deposits in speleothems using magnetic microscopy

IF 3.3 1区地球科学 Q1 GEOGRAPHY, PHYSICAL

Quaternary Science Reviews Pub Date : 2025-10-08 DOI:10.1016/j.quascirev.2025.109638

Samuel L. Piascik , Roger R. Fu , Nicolás M. Stríkis , Ricardo I.F. Trindade , Julio Cauhy Rodrigues , Francisco W. Cruz , Gelson F. Souza-Junior , Andrea Borsato , Vitor Azevedo , Plinio Jaqueto , Isabel Tamara Pedron , Perri Thaler , Maximilian Muradian , Hai Cheng

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引用次数: 0

Abstract

Changes in rainfall patterns, extreme precipitation events, and associated flooding or droughts represent a major hazard to societies worldwide. The concentration of ferromagnetic particles in speleothems has been recognized as a potential paleoclimate proxy that can be used in conjunction with existing proxy measurements to provide a more accurate interpretation of past cave conditions, paleoprecipitation, and paleohydrology. However, extracting paleoclimatic information from speleothems requires reliably differentiating among magnetic grain populations enhanced by rainfall, flooding, hiatuses, and other mechanisms. In this study, we focus on a speleothem from a section of Malfazido cave in southern Brazil with low airflow and that was subjected to repeated flood events. We use the Quantum Diamond Microscope (QDM) to produce micrometer-resolution magnetic maps of a portion of the central column corresponding to the past century to allow for comparison against existing instrumental precipitation records. These maps reveal several discrete, highly magnetic laminae enriched in coarse ferromagnetic particles (magnetic moments ≥10⁻¹³ Am²), as well as a population of lower moment grains found throughout all time intervals. Following comparison to the distribution of magnetic moments found in nearby flood-deposited mud samples, thin section optical microscopy, and the timeline of documented extreme rainfall events, we conclude that at least 9 of the magnetic layers were flood-deposited. Additionally, we observe a weak positive correlation between the magnitude of the lower moment grains and instrumental records of rainfall and streamflow throughout the sample, implying a rainfall-modulated dripwater origin for magnetic material found outside the highly magnetic laminae. These results demonstrate that grain-level characterization of magnetic properties using high-resolution magnetic microscopy can provide critical information to help discriminate between different modes of magnetic particle enhancement in speleothems and that this approach offers a novel method for reconstructing past flood frequency.

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利用磁显微镜可靠地鉴定洞穴中洪水沉积物

降雨模式的变化、极端降水事件以及相关的洪水或干旱是全球社会面临的主要危害。洞穴中铁磁颗粒的浓度已被认为是一个潜在的古气候指标，可以与现有的替代测量相结合，为过去的洞穴条件、古降水和古水文提供更准确的解释。然而，从洞穴中提取古气候信息需要可靠地区分降雨、洪水、中断和其他机制增强的磁性颗粒种群。在这项研究中，我们重点研究了巴西南部Malfazido洞穴的一段洞穴，该洞穴气流较低，并遭受了反复的洪水事件。我们使用量子钻石显微镜（QDM）制作了过去一个世纪中央柱部分的微米分辨率磁图，以便与现有的仪器降水记录进行比较。这些图揭示了几个离散的、富含粗铁磁粒子（磁矩≥10−13 Am2）的高磁性层，以及在所有时间间隔中发现的低磁矩颗粒群。通过与附近洪水沉积的泥浆样品的磁矩分布、薄片光学显微镜以及记录的极端降雨事件的时间轴进行比较，我们得出结论，至少有9个磁性层是洪水沉积的。此外，我们观察到低矩颗粒的大小与整个样品中降雨和水流的仪器记录之间存在微弱的正相关关系，这意味着在高磁性层状层外发现的磁性物质是降雨调制的水滴来源。这些结果表明，使用高分辨率磁显微镜进行粒度级磁性表征可以提供关键信息，帮助区分洞穴中不同模式的磁颗粒增强，并且该方法为重建过去的洪水频率提供了一种新方法。

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来源期刊

Quaternary Science Reviews 地学-地球科学综合

CiteScore

7.50

自引率

15.00%

发文量

388

审稿时长

3 months

期刊介绍： Quaternary Science Reviews caters for all aspects of Quaternary science, and includes, for example, geology, geomorphology, geography, archaeology, soil science, palaeobotany, palaeontology, palaeoclimatology and the full range of applicable dating methods. The dividing line between what constitutes the review paper and one which contains new original data is not easy to establish, so QSR also publishes papers with new data especially if these perform a review function. All the Quaternary sciences are changing rapidly and subject to re-evaluation as the pace of discovery quickens; thus the diverse but comprehensive role of Quaternary Science Reviews keeps readers abreast of the wider issues relating to new developments in the field.