TY - JOUR

T1 - Magnetic carriers and remanence mechanisms in magnetite-poor sediments of Pleistocene age, southern North Sea margin: Paper II.

AU - Maher, Barbara A.

AU - Hallam, D.F.

PY - 2005/1

Y1 - 2005/1

N2 - Pleistocene sedimentary sequences in the East Anglian region of Britain record both major and minor climatic oscillations, and the impact of isostatic and eustatic variations. Intensively studied in terms of their lithology and biostratigraphy, the sequences have been difficult to place in an absolute timeframe. Dating and correlation by magnetostratigraphy has been attempted over a number of years. However, these sediments are difficult to date by palaoemagnetic means because they are poor in detrital magnetite, subject to post-depositional deformation and diagenesis, and have unknown rates of sedimentation. Determining whether their natural remanence magnetisation (NRM) directions are reliable thus requires information on the mode and timing of remanence acquisition. Here, we apply palaeomagnetic, rock magnetic and mineralogical analyses to identify the NRM carriers in these sediments and hence their palaeomagnetic reliability. Within oxidised fluvial sediments (the Kesgrave Formation), the magnetic carriers appear to be relict magnetic minerals (ferrian ilmenites, chromites, haematite and goethite), which sometimes carry a reliable primary depositional remanence (DRM) but often an overprinting viscous (time-varying) remanence (VRM). Within some reduced marine and inter-tidal sediments (within the Crag basin), the iron sulphide, greigite, has been found to carry a reliable, `syn'-depositional chemical remanence (CRM). In all the sediments, magnetic inclusions within silicates are abundant, significant for the mineral magnetic signal but contribute little to any recoverable palaeomagnetic information.

AB - Pleistocene sedimentary sequences in the East Anglian region of Britain record both major and minor climatic oscillations, and the impact of isostatic and eustatic variations. Intensively studied in terms of their lithology and biostratigraphy, the sequences have been difficult to place in an absolute timeframe. Dating and correlation by magnetostratigraphy has been attempted over a number of years. However, these sediments are difficult to date by palaoemagnetic means because they are poor in detrital magnetite, subject to post-depositional deformation and diagenesis, and have unknown rates of sedimentation. Determining whether their natural remanence magnetisation (NRM) directions are reliable thus requires information on the mode and timing of remanence acquisition. Here, we apply palaeomagnetic, rock magnetic and mineralogical analyses to identify the NRM carriers in these sediments and hence their palaeomagnetic reliability. Within oxidised fluvial sediments (the Kesgrave Formation), the magnetic carriers appear to be relict magnetic minerals (ferrian ilmenites, chromites, haematite and goethite), which sometimes carry a reliable primary depositional remanence (DRM) but often an overprinting viscous (time-varying) remanence (VRM). Within some reduced marine and inter-tidal sediments (within the Crag basin), the iron sulphide, greigite, has been found to carry a reliable, `syn'-depositional chemical remanence (CRM). In all the sediments, magnetic inclusions within silicates are abundant, significant for the mineral magnetic signal but contribute little to any recoverable palaeomagnetic information.

KW - palaeomagnetism

KW - remanence acquisition

KW - British Pleistocene sequences

KW - Quaternary palaeomagnetism

U2 - 10.1002/jqs.894

DO - 10.1002/jqs.894

M3 - Journal article

VL - 20

SP - 79

EP - 94

JO - Journal of Quaternary Science

JF - Journal of Quaternary Science

SN - 0267-8179

IS - 1

ER -