A suite of simple rock magnetic measurements can characterize the mineralogy, abundance and comparative grain size distributions of the magnetic minerals within a sediment. This type of information is increasingly being utilized in Earth Sciences to discriminate sediment sources, because of its high degree of precision (<1 ppb of magnetite can be detected) and the simple and quick non-destructive methodology.
Magnetic minerals can range in size from a few nanometres to several hundred microns. For any specific magnetic mineralogy, sets of magnetic properties characterize the abundance, composition and grain size of the magnetic particles. Therefore suites of magnetic minerals with different grain size and composition have different magnetic characteristics, and different magnetic characteristics often occur in sediment from different contributing sources.
The measurements are best performed on sand grade sediments, which can be disaggregated (i.e sediment samples, core plugs, side wall cores or drill cuttings. The measurements are performed on specific fractions to remove the likelihood of hydrodynamic sorting effects.
The characterization is done using only those magnetic particles situated within host silicate grains. These provide the most reliable means for characterizing differences in provenance because they are isolated from diagenetic or weathering fluids.
Various magnetic measurements are undertaken. From these measurements distinct sources are identified using cluster analysis. From these data, either broad scale correlations can be proposed, or if end member sources can be well characterised, then mixing models can be developed for sediment budget studies.
Dr. Mark
Hounslow for further details (using m.hounslow, with dept address
@lancs.ac.uk)