Magnetic susceptibility contrasts in Ordovician greywackes of the Southern Uplands of Scotland

J. D. Floyd, A. Trench

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15 Citations (Scopus)


Ordovician greywacke formations of the Southern Uplands are demonstrated to have consistent differences in magnetic susceptibility, which parallel differences in petrography. The observed susceptibilities range from a minimum of 0.16 × 10-3SI for the quartz-rich, feldspar-poor Glenwhargen Formation to a maximum of 13.81 × 10-3SI for the quartz-poor, feldspar-rich Marchburn Formation, and are considered to be directly related to variation in the amount of detrital magnetite in the greywackes. Rapid measurement of magnetic susceptibility is demonstrated to be a valuable field technique for distinguishing otherwise uniform sedimentary sequences on the basis of differing magnetite content. Detailed field observations illustrate considerable variation in susceptibility within metre-scale sections perpendicular to bedding through graded sedimentary units, which may be caused by density and/or grain-size effects. Laboratory measurements of the intensity of natural remanent magnetisation in the petrographically contrasting Kirkcolm and Galdenoch formations show a similar variation to that observed in susceptibility. Thermally distributed, scattered magnetization directions indicate that no primary remanence has survived the low-grade burial metamorphic event in the Southern Uplands. -Authors

Original languageEnglish
Pages (from-to)77-83
Number of pages7
JournalJournal - Geological Society (London)
Issue number1
Publication statusPublished - 1989
Externally publishedYes


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