Discrimination of biogenic and detrital magnetite through a double Verwey transition temperature

Abstract

Magnetite occurs widely in natural environments in both inorganic and biogenic forms. Discrimination of the origin of magnetite has important implications, from searching for past microbial activity to interpreting paleomagnetic and environmental magnetic records in a wide range of settings. In this study, we present rock magnetic and electron microscopic analyses of marine sediments from the continental margin of Oman. Low‐temperature magnetic data reveal two distinct Verwey transition (Tv) temperatures that are associated with the presence of biogenic and inorganic magnetite. This interpretation is consistent with room temperature magnetic properties and is confirmed by electron microscopic analyses. Our study justifies the use of two distinct Tv temperatures as a diagnostic signature for discriminating inorganic and biogenic magnetite. Simple low‐temperature magnetic measurements, therefore, provide a tool to recognize rapidly the origin of magnetite within natural samples. In addition, our analyses reveal progressive down‐core dissolution of detrital and biogenic magnetite, but with preservation of significant amounts of fine‐grained magnetite within sediments that have been subjected to severe diagenetic alteration. We demonstrate that preservation of magnetite in such environments is due to protection of fine‐grained magnetite inclusions within silicate hosts. Our results, therefore, also provide new insights into diagenetic processes in marine sediments.

Paleomagnetic Secular Variations During the Past 40,000 Years From the Bay of Bengal

“…We speculate that the constituent magnetic minerals within these four cores are magnetite, as has also been suggested by Li et al (2006). The LTC curves of five samples from core BOB-24 exhibit clear Verwey transitions (Verwey, 1939) around 120 K as an indication of detrital magnetite (Chang et al, 2016). The LTC curves of five samples from core BOB-24 exhibit clear Verwey transitions (Verwey, 1939) around 120 K as an indication of detrital magnetite (Chang et al, 2016).…”

Widespread occurrence of silicate‐hosted magnetic mineral inclusions in marine sediments and their contribution to paleomagnetic recording

“…This microstructure is consistent with that of exsolved magnetite in igneous rocks. The presence of magnetic mineral inclusions in samples from core CD143‐55705 from the Arabian Sea confirms expectations from magnetic analyses (Figures e and f [ Chang et al ., ]). TEM analysis on sample RR0603‐03JC‐2‐60 indicates the presence of abundant biogenic magnetite crystals, as evidenced by apparently intact magnetosome chain structures and well‐defined magnetosome crystal morphologies (Figure b).…”

Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan

“…Therefore, an offset between the forcing and the resulting diagenetic signature is expected (i.e., through variable influx, burial, and degradation of OC) due to diffusion of pore fluids at dissolution fronts that is affected by degradation of the overlying OC. Identification of the active sulfidic dissolution front that occurs within the uppermost part of a core site [e.g., Karlin , ; Riedinger et al ., ; Rowan et al ., ; Roberts , ; Chang et al ., ] provides a means to estimate the diagenetic lag with respect to the forcing. Two distinct zones are observed within the upper meter of core MD01‐2421 (Figure ).…”