12,000

We have over 12,000 students, from over 100 countries, within one of the safest campuses in the UK

93%

93% of Lancaster students go into work or further study within six months of graduating

Home > Research > Publications & Outputs > Magnetic mineralogy of sandstones from the Lund...
View graph of relations

« Back

Magnetic mineralogy of sandstones from the Lunde Formation (late Triassic), northern North Sea, UK: origin of the palaeomagnetic signal

Research output: Contribution in Book/Report/ProceedingsChapter (peer-reviewed)

Published

Publication date1995
Host publicationPalaeomagnetic applications in hydrocarbon exploration and production
EditorsPeter Turner, Amanda Turner
Place of publicationLondon
PublisherGeological Society of London
Pages119-147
Number of pages28
Volume98
ISBN (Print)978-1-897799-42-0
Original languageEnglish

Abstract

The minerals responsible for the magnetic properties of the Late Triassic Lunde Formation have been examined using a combination of magnetic mineral extraction, microscopy and rock magnetic measurements. The magnetic mineralogy is controlled by the depositional environment and the effects of diagenesis, by a process of differential preservation and modification of the original detrital minerals. The magnetic susceptibility and remanence properties of the sediments are strongly influenced by the proportion of silt and clay sized clastic material, which contains most of the magnetic minerals. Paramagnetic minerals, both of depositional origin and produced during diagenesis, are largely responsible for the magnetic susceptibility. A suite of residual ferrimagnetic oxides (chromite and Mn-substituted magnetite) is responsible for the remanence properties in grey sandstones, because most of the originally deposited magnetic Fe-Ti oxides have been removed by reducing conditions during diagenesis. However, a small number of reddened horizons preserve a higher proportion of original detrital Fe-Ti oxides (ferrimagnetic ilmenite, ferrimagnetic chromite and magnetite), although authigenic hematite has replaced most of the original mineralogy in the reddened horizons. Magnetic oxide inclusions in quartz and feldspars are important contributors to the remanence signal, particularly in horizons which have a low content of discrete detrital ferrimagnetic grains, either through diagenetic dissolution, or paucity of the silt and clay fraction. Within the grey sandstones, the Triassic palaeomagnetic signal is carried by magnetite as inclusions in detrital silicates, with a contribution from detrital ferrimagnetic chromite. A model of the effects of diagenesis on the magnetic mineralogy in deeply buried sequences is proposed.