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- Title
The influence of particle size variations on the magnetic properties of sediments from the north-eastern Irish Sea
- Authors
Oldfield, Frank; Lizhong Yu
- Abstract
This paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the Irish Sea. Principal component ordinations of the results show a close link between magnetic property variations and particle size. The magnetic properties of a subset of samples, particles sized by a combination of sieving and pipette analysis, confirm that variations in ferrimagnetic ('magnetite') grain size parallel those in particle size, despite the fact that the magnetic grains in the fine grades have diameters 1-2 orders of magnitude smaller than those of the particle size fraction in which they occur. This is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4φ as an artifact of the pipetee method. Most samples have a biomodal distribution of magnetic minerals, with a coarse mode associated with heavy minerals in the sands or coarse silts, and a fine mode in the clays. Magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) largely picks out the fine mode. The results open up the possibility of normalizing samples from these environments for particle size and, more specifically, clay content, by means of ARM or ARM/χ values. The most likely source for the uniform and almost exclusive stable single domain magnette, which dominates the magnetic properties of the clays, is thought to be bacterial magnetosomes. The measurements as a whole do not appear to hold much promise for discriminating sediment source types.
- Subjects
IRISH Sea; SEDIMENTS
- Publication
Sedimentology, 1994, Vol 41, Issue 6, p1093
- ISSN
0037-0746
- Publication type
Article
- DOI
10.1111/j.1365-3091.1994.tb01443.x