Peru Basin sediments: Diagenetic implications of a low coercivity overprint of the NRM

Abstract

Abstract.Two coexisting populations of magnetite that vary by at least 320kyr in age characterize the magnetomineralogy in oxic through suboxic

Low‐temperature magnetic properties of pelagic sediments (Ocean Drilling Program Site 805C): Tracers of maghemitization and magnetic mineral reduction

“…The appearance of the Verwey transition below the iron redox boundary suggests a change in magnetic mineralogy apparently controlled by biogeochemical processes. Similar downcore behavior was observed in M•Zs • curves from hemipelagic sediments of ODP Sites 976D and 977A (western Mediterranean) [Torii, 1997] and from sediments of the Peru basin [Urbat and Dekkers, 1999]. Following Torii [1997], we attribute the differential appearance of the Verwry transition to the low-temperature oxidation of magnetite and its subsequent dissolution below the iron redox boundary.…”

“…Some of these processes, combined with the dissolution of oxidized coatings, could result in lower coercivities and the preferential acquisition of viscous magnetization (VRM) overprints. Temporal changes in iron reduction [Tarduno, 1994], coercivity changes, and VRM acquisition offer an alternative explanation for differential NRM overprinting observed in some marine sediments and suggested to be caused by the production of secondary, slightly oxidized magnetite at depth [e.g., Urbat and Dekkers, 1999]. Figure 12b).…”

Iron oxide formation in the active oxidation front above sapropel S1 in the eastern Mediterranean Sea as derived from low-temperature magnetism

“… Schematic representation of the most important diagenetic processes for the magnetic mineralogy during sapropel formation (Passier et al 1996, 1997), sapropel burial (Higgs et al 1994; van Santvoort et al 1996), formation of a new sapropel on top of a buried sapropel and the resulting magnetic intensities. Sapropels were anoxic/sulphidic during deposition, and reductive dissolution and subsequent pyritization of Fe oxides in this period caused a decrease of magnetic intensities in and below the sapropel.…”

“…Previous studies of low‐temperature magnetic remanence around the oxic–suboxic redox boundary in marine sediments have mainly focused on relatively homogeneous (hemi)pelagic settings with the oxic–suboxic boundary at a few metres below the seafloor (Torii 1997; Urbat & Dekkers 1999; Smirnov & Tarduno 2000). In the western Mediterranean Sea (Torii 1997) and in the western equatorial Pacific Ocean (Tarduno 1995; Tarduno & Wilkison 1996; Tarduno et al 1998; Smirnov & Tarduno 2000), the main conclusion of these studies was that the Verwey transition is only evident below the oxic–suboxic boundary.…”

“…Size reduction of coarse magnetite grains leads to enhanced superparamagetism just before complete removal of these grains. In Peru Basin sediments, an NRM overprint was reported from secondary magnetite formed below the oxic-suboxic boundary, which showed the Verwey transition (Urbat & Dekkers 1999).…”