Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum

Abstract

We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 m long and hexaoctahedral prisms up to 1.4 m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability-a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming-drove diversification of magnetite-forming organisms, likely including eukaryotes.biomineralization ͉ electron microscopy ͉ magnetofossil

Structural Modification and Self-Assembly of Nanoscale Magnetite Synthesised in the Presence of an Anionic Surfactant

“…were observed having 80-100nm dimensions forming 1D stacks of up to 4 µ m in length. Recently, very similar magneto-fossils formed by magnetotactic bacteria have been reported [18]. Whiskers with an aspect ratio 1:10 (compound 3, Figures 6a-c.), typically around 100-200 nm in length, also form and these self-assemble into 2D hexagonal plate and 3D "flower" motifs.…”

Chemical signature of magnetotactic bacteria

“…This method could be particularly suitable for ancient terrestrial magnetite samples for which no other criteria can help in establishing their origin (1, 2). Other natural magnetite samples that have been suggested to be from biological origin could be reinvestigated for their chemical composition (18,39). To our knowledge, trace element data including strontium/calcium ratio in natural magnetite and analyses of cogenetic associated calcium carbonates are not available in the literature, preventing any application of the present method.…”

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

“…Magnetosome abundance in sediments is strongly controlled by the availability of particulate iron and organic carbon flux to the seafloor (Roberts et al, 2011), which can be related to climate, including hyperthermal conditions (e.g. Schumann et al, 2008;Chang et al, 2012;Larrasoaña et al, 2012).…”