Magnetic Anisotropy of Rocks: A new Classification of Inverse Magnetic Fabrics to Help Geological Interpretations

Inverse magnetic fabrics defined by anisotropy of magnetic susceptibility with the longest principal axis perpendicular to bedding were identified in the studied samples of Ordovician sedimentary rocks from the Barrandian area, Czech Republic. These fabrics are related to ankerite fibers in association with cone-in-cone structures. To understand the meaning of such inverse magnetic fabrics for geological interpretations, a new, more detailed classification of inverse magnetic fabrics' types is formulated in this paper. Distinguishing the structural (i.e., shape) and magnetocrystalline anisotropies in rocks, three new (sub)types of magnetic fabrics were defined in this study based on the combination of structural normal/inverse and magnetocrystalline normal/inverse anisotropies. As a result, normal magnetic fabric is extended by new fabric types associated with inverse anisotropy: simple inverse, pure inverse, and pseudo-normal magnetic fabrics. The studied fibrous ankerite shows simple inverse magnetic fabric, which results from the combination of normal magnetocrystalline and inverse structural anisotropies.