Magnetic anisotropy of clayey and silty members of tertiary flysch from the Silesian and Skole nappes (Outer Carpathians)

Abstract

AMS studies earlier carried out on the flysch sediments from the Outer Western Carpathians focused on the sandstone members deposited from turbidity currents. The main conclusion of these studies was that the dominant features of the AMS fabric developed during sedimentation and the tectonic overprint was weak. In recent years a large number of claystone (deposited also from turbidity currents, but in calm water) localities were sampled from the Krosno beds of the Silesian nappe, primarily for paleomagnetic study. Nevertheless, the AMS of the samples was also measured. The magnetic fabrics of the claystones were dominated by foliation, but lineations were also expressed and attributed to deformation. The question arose how different are the reactions of the claystone and the siltstone beds to deformation.Comparison was made between the upper, finest grained part of sandstone beds and claystones from the same outcrops of the Silesian nappe. It was found that the AMS ellipsoids for different lithologies were coaxial. The main difference was the higher degree of foliation in the claystones than in the siltstones which was attributed to stronger compaction in the former. Surprisingly, there was practically no difference in the degrees of lineation between the different lithologies from the same outcrop, suggesting that the siltstones and the intercalated claystones similarly react to tectonic deformation. Siltstone and claystone samples from a single outcrop from the Skole nappe behaved differently, since the siltstone had inverse fabric due to impregnation by siderite.It seems that the claystones of the flysch sequences, although technically more difficult to work with them, have advantages over the sandstones/siltstones when the goal of the AMS measurements is the study of deformation. One of the good aspects of the claystones is that their primary fabric is probably not or weakly oriented by paleocurrents. Therefore, the AMS lineation and the stress field orientation have a straightforward relation, while the sandstones often have a composite fabric, since it is the well developed flow oriented sedimentary fabric which is overprinted by deformation. The second is that the permeability of claystones is lower, thus secondary infiltration and impregnation by E. Márton et al. 122Stud. Geophys. Geod., 54 (2010) iron minerals dramatically influencing the orientation of the AMS fabric, as it was observed for the siltstones from a single locality from the Skole nappe, is practically impossible.

An integrated paleomagnetic and magnetic anisotropy study of the Oligocene flysch from the Dukla nappe, Outer Western Carpathians, Poland

“…Inverse fabric can be due to the presence of either single domain magnetite or siderite (Tarling & Hrouda 1993;Chadima et al 2006). In the present case, after heating the samples to 460 °C, the fabric becomes normal (PL 1456, 460 °C max: 162/18, int: 71/5, min: 327/71), which points to the decomposition of siderite, similarly to the case in the Skole nappe (Márton et al 2010).…”

A multidisciplinary study of the Lower Cretaceous marine to continental transition in the northern Austral-Magallanes basin and its geodynamic significance

“…In summary, the original AMS fabric is not parallel to the ferromagnetic fabric, and shows an inverse relation with the bedding plane; therefore it is interpreted as carried by a mineral with inverse relation between elongation and magnetic susceptibility. The switching occurred after heating, denotes that the inverse fabric was either destroyed, or overcome by the influence of newly formed minerals with normal fabric (see for example Chadima et al, 2006;Márton et al, 2010;Kiss et al, 2016). The anomalous original magnetic fabric is probably due to the balance between the inverse magnetic fabric produced by minerals like goethite, Fe-bearing carbonate (siderite) or SD elongated magnetite, and the normal magnetic fabric due to the paramagnetic matrix and other magnetic minerals.…”

Anisotropy of magnetic susceptibility as an indicator for palaeocurrent analysis in folded turbidites (Outer Western Carpathians, Poland)

“…1B; Hrouda & Stráník, 1985; Stráník et al , 2007) or mainly represent the first stage of tectonic overprinting, characterized by sedimentary foliation accompanied by tectonic lineations (Fig. 1E; Hrouda & Potfaj, 1993; Hrouda et al , 2009; Márton et al , 2009; Márton et al , 2010; Szaniawski et al , 2013; Kiss et al , 2016; Nawrocki et al , 2016; Szaniawski et al , 2017). In the latter case, a phenomenon widespread in areas where folding and thrusting were significant (e.g.…”