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Magnetic mineralogy of pelagic limestones

2007; Wiley; Volume: 85; Issue: 2 Linguagem: Inglês

10.1111/j.1365-246x.1986.tb04522.x

2056-5216

R. Freeman,

Geology and Paleoclimatology Research

Due to their extremely small size and low concentration, the carriers of magnetization in limestones are usually identified through indirect rock magnetic methods. This paper describes a method for extracting tiny ferromagnetic grains from consolidated calcareous rocks and summarizes a scanning electron microscope (SEM) investigation of magnetic phases from several palaeomagnetically important pelagic limestones. Details of surface characteristics and elemental composition are readily accessible with the SEM and complement normal rock magnetic experiments in giving a more complete assessment of the major ferromagnetic phases, their origin, and the timing and acquisition of magnetization. The results confirm many indications of the indirect methods and introduce several important new features. In addition to detrital titanomagnetite, diagenetic titanohaematite and iron sulphides, there is a significant contribution by authigenic microcrystalline haematite, detrital cosmic spherules, chromian spinels, and skeletal titanomaghaemite.