Comparing Paleointensity Recording Efficiencies of Detrital and Biogenic Magnetite by Deposition Experiments With Synthetic Sediments

Abstract Marine sediments contain magnetic mineral particles of detrital, biogenic and authigenic origin that record changes in the direction and intensity of the geomagnetic field over geological time. Previous studies have demonstrated that the recording efficiencies of detrital and biogenic magnetite differ. Varying mixing proportions of these two primary magnetic carriers and the gradual collapse of magnetofossil chains through time should therefore modify and bias the relative paleointensity (RPI) signal. To investigate both effects, we conducted laboratory sedimentation experiments using synthetic magnetite powder of vortex to multidomain state as a detrital magnetization carrier, and extracted magnetosome crystals from Magnetospirillum gryphiswaldense MSR‐1—with and without previous ultrasonic treatment—as a biogenic magnetization carrier. Both magnetite types were suspended in kaolin‐water slurries and deposited in magnetic fields of 50 and 70 μT. RPI values derived from depositional (DRM), anhysteretic (ARM) and isothermal (IRM) remanent magnetization showed that the magnetic recording efficiencies of ordered and disordered magnetofossil were 1.7–5.3 times lower in comparison to ground synthetic magnetite. These experiments show the lower DRM acquisition efficiency of biogenic in relation to detrital magnetite. Our study sheds new light on the contrasting sedimentary magnetic recording efficiencies of detrital and biogenic magnetite, which may imply environmental bias in geomagnetic field intensity reconstructions.