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

Abstract

Two coexisting populations of magnetite that vary by at least 320 kyr in age characterize the magnetomineralogy in oxic through suboxic Peru Basin sediment (7°04′S / 88°28′W). 1) Primary magnetite barely underwent post-depositional alteration and yields a straightforward magnetostratigraphy (Brunhes Chron - top of Olduvai Subchron). 2) A stable, low-coercivity overprint of the NRM resides in secondary, slightly oxidized SD magnetite that recorded the Brunhes Chron direction. The secondary magnetite appears at the modern Fe-redox boundary (2.6mbsf) and continues downhole to abruptly disappear at 5.3mbsf in the Matuyama Chron. It can be discerned by combined analyses of directional data and the Verwey transition in low-temperature remanence measurements (20-300 K) that appears concomitant with the overprint.