Rock-magnetic Properties of Deep-sea Sediments from the Shatsky Rise: Anomalous Sedimentary Environments During MIS 6 and 8

Abstract

Rock-magnetic properties of deep-sea sediments from the Shatsky Rise (32°17.55’ N, 158°13.57’ E) were investigated to understand changes of sedimentary environments over glacial-interglacial cycles. Correlation of magnetic susceptibilities with a nearby core reveals ~300 ka at the depth of ~520 cm and an average sedimentation rate of ~1.73 cm/ky. Magnetic parameters show significant deviations from a general down core trend at the depth of ~250&#8211 330 cm and ~430&#8211 500 cm, corresponding to the MIS 6 and 8, respectively. In those horizons, concentration-related magnetic parameters (e.g., magnetic susceptibility, ARM and SIRM) decrease abruptly in magnitude, associated with reduced contribution of low-coercivity minerals (decrease of S-ratio). The drops are also concordant with grain-size coarsening (decrease of ARM/SIRM). Such anomalous rock-magnetic properties can be attributed to the change of the major eolian source, which can provide high-coercivity mineral rich sediments. Increased input of high-coercivity minerals could result in decreases of S-ratio and the magnetic concentration parameters due to their low magnetization. Alternatively, as a result of post-depositional alteration (i.e., diagenesis), fine-grained magnetite preferentially can be dissolved. In this case, the remaining magnetic minerals would have larger average grain-size, higher fraction of high-coercivity minerals, and thus, produies with a nearby core reveals ~300 ka at the depth of ~520 cm and an average sedimentation rate of ~1.73 cm/ky. Magnetic parameters show significant deviations from a general down core trend at the depth of ~250&#8211 330 cm and ~430&#8211 500 cm, corresponding to the MIS 6 and 8, respectively. In those horizons, concentration-related magnetic parameters (e.g., magnetic susceptibility, ARM and SIRM) decrease abruptly in magnitude, associated with reduced contribution of low-coercivity minerals (decrease of S-ratio). The drops are also concordant with grain-size coarsening (decrease of ARM/SIRM). Such anomalous rock-magnetic properties can be attributed to the change of the major eolian source, which can provide high-coercivity mineral rich sediments. Increased input of high-coercivity minerals could result in decreases of S-ratio and the magnetic concentration parameters due to their low magnetization. Alternatively, as a result of post-depositional alteration (i.e., diagenesis), fine-grained magnetite preferentially can be dissolved. In this case, the remaining magnetic minerals would have larger average grain-size, higher fraction of high-coercivity minerals, and thus, produ