Biogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil-rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet-shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet-shaped magnetofossils produce variable FORC (first-order reversal curve) central-ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet-shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet-shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records.

中文翻译：

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磁化石矫顽力分量的起源：来自耦合实验观察和微磁计算的约束


沉积物中由趋磁细菌 （MTB） 和相关的磁硅产生的生物磁铁矿晶体具有可变形态、粒度和链结构的特点。磁石广泛用于古地磁和古环境研究，但复杂的磁化石形状和颗粒排列会显着影响磁特性，阻碍其磁性检测和代理解释。在这里，我们对典型的富含磁磷硅的沉积物进行耦合实验和微磁建模分析，其中磁化石晶体形式和微观结构对磁性能的影响可以定量分离。由于沉积物中的原位磁化石链结构仍然知之甚少，我们比较了基于真实磁化石形状和粒度分布的磁性测量和微磁模拟的结果。我们的结果表明，子弹形磁铁肯定有助于生物硬 （BH） 矫顽力分量，细长的棱柱形颗粒和坍缩的等维颗粒对生物软 （BS） 分量的贡献很小。使用子弹形磁垢的不同坍塌模型的微磁模拟产生了具有相似矫顽力分布的可变 FORC（一阶反转曲线）中心脊贡献。敏感性测试表明，如果子弹状颗粒的比例大于 ∼2%，则含有不同形式磁铁的样品可以产生 BH 矫顽力分量。子弹状颗粒比例较高的磁化石组合具有较高的矫顽力、垂直比和较大的 BH 含量。 我们的数据为理解磁化石矫顽力分量的起源和沉积物中的原位磁化石微观结构提供了新的思路，这对于解释地质记录中的磁化石代理信号非常有用。