Publication details
Tectonic vs. anomalous magnetic fabrics in sedimentary rocks: a case study from Barrandian, Czech Republic
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| Year of publication | 2013 |
| Type | Conference abstract |
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| Description | The study was focused on Ordovician sedimentary rocks and their anisotropy of magnetic susceptibility (AMS). The area under study is situated in the Prague Synform, Bohemian Massif, Czech Republic. Sedimentation in the basin began by Ordovician transgression and continued with siliciclastic rocks to Lower Silurian. The Upper Silurian is typical by carbonatic rocks as well as Devonian. The Silurian and Devonian sedimentary rocks are intensely folded and thrusted, while the Ordovician-rock deformation is not visible. The aim of the study was to find out whether the Ordovician rocks are actually un-deformed or were affected by strain by using AMS. Over 1500 samples were taken from 55 sites throughout dozen Ordovician formations. Temperature dependence of magnetic susceptibility was measured on the samples as well as AMS, which was compared to structural analysis of individual localities. In some specific cases, x-ray analysis or microscopic studies were done. Results and interpretations: 1) Analysis of temperature dependence of magnetic susceptibility showed that all Ordovician formations are controlled by paramagnetic minerals. 2) In majority sites normal sedimentary or strain fabrics were recognized. In these sites structural studies were mostly done but there were also found inverse and intermediate fabrics. 3) Inverse fabrics found in 4 sites were caused by fibrous ankerite. Fibers were grown perpendicularly to the bedding plane in the fibrous microveins and cone-in-cone textures. The maximum susceptibility direction is parallel to crystallographic c-axis of ankerite in the samples. 4) Intermediate fabrics or their relics were exclusively linked to all localities in two basal Ordovician formations. In this case, we cannot speculate about simple combination of normal and inverse fabrics but about autoregulatory diagenetic processes. |