Discovery of giant magnetofossils within and outside of the Palaeocene-Eocene Thermal Maximum in the North Atlantic

A Depth‐Transect of Ocean Deoxygenation During the Paleocene‐Eocene Thermal Maximum: Magnetofossils in Sediment Cores From the Southeast Atlantic

“…TEM observations reveal the presence of giant needle‐shaped magnetofossils in addition to conventional magnetofossils within the studied CIE sediments. The giant needle‐shaped magnetofossils visually have a relatively higher concentration at sites 1263 (∼1,500 m paleodepth) (Chang et al., 2018) and 1265 (∼1,800 m paleodepth) than at the three deep sites (1266, 1267, and 1262) (∼2,600–3,600 m paleodepth), likely reflecting different paleoenvironmental conditions, with the boundary at a paleodepth of ∼1,800–2,600 m. Although the origin of needle‐shaped magnetite crystals remains unknown, similar crystals observed in a bacterium of ∼4 μm in length (Vali & Kirschvink, 1991) and morphological analysis suggest a biogenic origin (Chang et al., 2012; Schumann et al., 2008; Xue et al., 2022). Previous studies hypothesized that expanded suboxic diagenetic zones probably provided more appropriate conditions for the iron biomineralization of "giant" magnetofossils (e.g., Chang et al., 2012, 2018; Schumann et al., 2008; Wagner, Egli, et al., 2021; Wagner, Lascu, et al., 2021).…”

“…However, subsequent studies identified abundant magnetite nanoparticles in sediment samples from the CIE intervals in nearby regions and demonstrated a biogenic rather than a bolide origin of the magnetite particles (Kopp et al., 2007, 2009; Lippert & Zachos, 2007; Schumann et al., 2008; Wagner, Egli, et al., 2021; Wagner, Lascu, et al., 2021). A growing number of studies suggest that magnetofossils are widespread in pelagic sediments across the PETM from different geological settings (e.g., Chang et al., 2012, 2018; Larrasoaña et al., 2012; Xue et al., 2022).…”

“…Several studies investigated magnetofossils across the PETM in different oceanic settings (Chang et al., 2012, 2018; Kopp et al., 2007, 2009; Larrasoaña et al., 2012; Lippert & Zachos, 2007; Schumann et al., 2008; Wagner, Egli, et al., 2021; Wagner, Lascu, et al., 2021; Wang et al., 2015; Xue et al., 2022). Some studies have suggested the magnetic particles as abiotic (Kent et al., 2003, 2017), although multiple lines of evidence and reason point to a microbial origin (Dickens, 2008).…”

Magnetofossils and Benthic Foraminifera Record Changes in Food Supply and Deoxygenation of the Coastal Marine Seafloor During the Paleocene‐Eocene Thermal Maximum

“…As such, EM1 represents the abundance of giant magnetofossils that have, so far, only been found in sediments deposited during the Paleocene and Eocene (Chang et al., 2012, 2018; Kopp et al., 2009; Schumann et al., 2008; Wagner, Egli, et al., 2021; Xue, Chang, Pei, et al., 2022). Although their origin is still unknown, their unusual shapes, iron oxide mineralogy, and crystal structures are consistent with a biogenic origin (Schumann et al., 2008; Xue, Chang, Pei, et al., 2022). Given their size, these giant magnetofossils were most likely produced by eukaryotes, rather than by bacteria.…”

MagNet: Automated Magnetic Mineral Grain Morphometry Using Convolutional Neural Network

“…However, there is currently no standardized approach for extracting and quantifying morphological information of magnetic mineral grains from microscopic images. Researchers often manually measure the size distribution of magnetic mineral grains in TEM/SEM images using some image processing software, such as Adobe Photoshop (e.g., Li & Pan, 2012) and ImageJ (e.g., Li et al., 2016; Maher et al., 2016; Xue et al., 2022). The need to process and measure manually the extensive TEM image datasets leads to time‐consuming procedures and also artificial errors.…”