Magnetic carriers and remanence mechanisms in magnetite-poor sediments of Pleistocene age, southern North Sea margin

Autor: D. F. Hallam, Barbara A. Maher
Rok vydání: 2005
Předmět:
Zdroj: Journal of Quaternary Science. 20:79-94
ISSN: 1099-1417
0267-8179
DOI: 10.1002/jqs.894
Popis: 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 num- ber of years. However, these sediments are difficult to date by palaeomagnetic means because they are poor in detrital magnetite, are 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 (fer- rian ilmenites, chromites, haematite and goethite), which sometimes carry a reliable primary deposi- tional remanence (DRM) but often an overprinting viscous (time-varying) remanence (VRM). Within some reduced marine and intertidal 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, are significant for the mineral magnetic signal but contribute little to any recoverable palaeomagnetic information. Copyright 2005 John Wiley & Sons, Ltd.
Databáze: OpenAIRE
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