An integrated magnetic susceptibility anisotropy (AMS) and structural geological study on Cenozoic clay-rich sediments from the Transdanubian Range

Abstract

Systematic structural and anisotropy of magnetic susceptibility (AMS) measurements were carried out on Cenozoic clay-rich deposits from the Transdanubian Range, central part of the Alcapa Unit. The aim was to improve the knowledge of the Neogene tectonic evolution of the area and of the connection of the stress field and the magnetic fabric of the sediments. The measurements of AMS revealed dominant foliation with weak lineation for Middle Eocene-Lower Miocene sediments. The directions of AMS lineation are aligned either with the direction of NNE-SSW extension of a strike slip phase or with the direction of NE-SW extension of the main rifting phase of the Pannonian Basin (19-14 Ma).The studied Late Miocene sediments have foliated AMS fabric, maximum and intermediate AMS directions are intermixed, and the AMS fabrics do not show any sign of tectonic deformation. In contrast, joints and faults were observed in the same rocks. Detailed structural analysis shows two extensional phases between ca. 10-4 Ma, with E-W to WNW-ESE and with NW-SE extension, respectively, and the youngest neotectonic strike-slip phase. The contrast between the presence of markers of brittle deformation and the absence of tectonically-induced AMS lineation is striking, since the same types of sediments in the South Pannonian basin show just the opposite. The explanation may be that northward-moving and CCW-rotating Adria caused strong compression in the southern Pannonian Basin, resulting in ductile deformation of the clay-rich sediments and systematic reorganization of AMS texture, while in our study area sediments of similar character and age were at a larger distance from the strongly deforming basin part.

Results, problems and future tasks of palaeostress and fault-slip analyses in the Pannonian Basin: the Hungarian contribution

“…The stress fields of SIPOS-BENKŐ et al (2014), derived from the entire TR, were basically similar to those found by earlier studies (MÁRTON & FODOR 2003, FODOR 2008. The notable exceptions were the Late Miocene stress fields they assumed a change in minimal stress direction from E-W to NW-SE being coeval with a counterclockwise rotation event (Figure 1, C).…”

“…The combination of fault-slip and palaeomagnetic data made also a progress integrating anisotropy of magnetic susceptibility (AMS) data. SIPOS-BENKŐ et al (2014) used AMS data to infer early stage deformation and compare AMS and stress axes within the TR. AMS axes shows good correlation with one of the earliest stress axes, thus it has been proved to be successful measure for deformation in sediments.…”

“…These are the post-Middle Miocene rotations within the Transdanubian Range, indicated by palaeomagnetic data (MÁRTON et al 2006). Such a rotation could be reflected in stress data, but for Late Miocene, they have poor temporal constraints (SIPOS-BENKŐ et al 2014) and it is not clear if differences in stress axes are due to local variations or to the rotation. In addition, map-scale structures do not reflect any Late Miocene deformation which would be suitable to accommodate larger than 20° rotations; thus these rotations should be local but even such map-scale structures are still missing.…”

Late Miocene sedimentary record of the Danube/Kisalföld Basin: interregional correlation of depositional systems, stratigraphy and structural evolution

“…Fault kinematics varied from normal to transtensional strike-slip (mostly sinistral oblique-slip) although it can mostly be deduced from outcrop-scale fault-slip data (e.g., Fodor 1991;Vojtko et al 2011;Sipos-Benkő et al 2014;Klučiar et al 2016). Stress calculations would suggest E -W to SE -NW tension although it is not clear if the different values indicate spatial or temporal variations (see Marko et al 1995;Fodor et al 1999;Hók et al 1999;Marko 2012;Sipos-Benkő et al 2014, Kovács et al 2015.…”

“…Stress calculations would suggest E -W to SE -NW tension although it is not clear if the different values indicate spatial or temporal variations (see Marko et al 1995;Fodor et al 1999;Hók et al 1999;Marko 2012;Sipos-Benkő et al 2014, Kovács et al 2015. The Late Miocene extensional tectonic regime with NW-SE directed Sh min persisted in the northern part of the basin up to the Middle Pleistocene.…”