The University of Southampton
University of Southampton Institutional Repository

Why are geomagnetic excursions not always recorded in sediments? Constraints from post-depositional remanent magnetization lock-in modelling

Roberts, Andrew P. and Winklhofer, Michael (2004) Why are geomagnetic excursions not always recorded in sediments? Constraints from post-depositional remanent magnetization lock-in modelling Earth and Planetary Science Letters, 227, (3-4), pp. 345-359. (doi:10.1016/j.epsl.2004.07.040).

Record type: Article


Many geomagnetic excursions have been documented during the Brunhes Chron. However, high-resolution paleomagnetic studies of sediments often provide evidence of few (if any) excursions. We have investigated the reasons for this observation by modelling the post-depositional remanent magnetization (PDRM) lock-in process. A cubic lock-in function produces more rapid lock-in compared to linear and exponential functions proposed in the literature. We therefore used a cubic function to model “best-case" scenarios for the quality of the paleomagnetic record when a high-frequency geomagnetic input signal is convolved with the sediment lock-in function for a wide range of sedimentation rates. Even for a lock-in depth of 10 cm, where 95% of the PDRM is locked in 5 cm below the surface mixed layer, an input signal containing abundant excursions (with 1-kyr duration) is smoothed so drastically at low sedimentation rates (1–3 cm/kyr) that no excursions are recorded. Excursions are further attenuated by increasing the lock-in depth, as well as by sampling at discrete stratigraphic intervals. The PDRM process acts as a low-pass filter for high-frequency secular variation signals even at moderate sedimentation rates (>10 cm/kyr). We have also modelled the effects of modulation of sedimentation rate by a climatic forcing function (e.g., insolation). Even though the average sedimentation rate might be substantial, PDRM recording becomes much less reliable in intervals where sedimentation rates are lowest. In these cases, some excursions are reliably recorded in detail, while others may not be recorded at all. Our modelling suggests that in order to consistently detect the presence of geomagnetic excursions, it is ideal to work with sediments that maintain minimum sedimentation rates above 10 cm/kyr. If the normal spectrum of geomagnetic field behaviour contains abundant excursions, failure to document excursions in many apparently high-resolution analyses probably results from PDRM lock-in within relatively slowly deposited sediments, or to unrecognized intervals of slow sedimentation in environments with higher average sedimentation rates.

Full text not available from this repository.

More information

Published date: 15 November 2004
Keywords: post-depositional remanent magnetization, pdrm, geomagnetic, excursions, magnetization, lock-in, sediment


Local EPrints ID: 13504
ISSN: 0012-821X
PURE UUID: a60ce0cf-0177-42e2-b907-2690befb61bc

Catalogue record

Date deposited: 07 Dec 2004
Last modified: 17 Jul 2017 17:02

Export record



Author: Andrew P. Roberts
Author: Michael Winklhofer

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton:

ePrints Soton supports OAI 2.0 with a base URL of

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.