Magnetic fabrics in the turbidite deposits of the Central Carpathian Paleogene Basin in relation to sedimentary and tectonic fabric elements

Abstract

Anisotropy of magnetic susceptibility and anisotropy of anhysteretic remanent magnetization were studied in the Oligocene turbidites of the weakly deformed Central Carpathian Paleogene Basin. In order to decide whether the magnetic fabric can be related to deposition from a paleoflow or to incipient weak tectonic deformation we compared magnetic fabrics in individual intervals of the Bouma sequence with sedimentary structures and tectonic brittle mesostructures (joints). In the Ta–Te intervals we observed a good correlation between maximum susceptibility axes and SW(W)–NE(E) oriented paleoflows. Within convoluted and slump folded sandstones the AMS fabric coincides with the orientation of soft-sediment deformation structures. These features suggest the sedimentary origin of the AMS fabric. Three types of AARM sub-fabric were distinguished. The AARM type 1 represents magnetic foliations parallel either to NNW–SSE or to NE–SW oriented joints with magnetic lineations distributed along the joins. In the AARM type 2 magnetic foliations remained parallel to the bedding while magnetic lineations group around the joint to bedding intersections. The AARM type 3 coincides with the AMS fabric. Magnetic and microscopic analyses indicate that the AARM fabrics are connected to magnetite associated with subordinate ferrimagnetic iron sulphides. Both minerals occur in a sub-microscopic size and formed most likely during late diagenesis through the alteration of pyrite, possibly accompanied by burial clay transformation processes. The growth of the authigenic ferrimagnetic minerals was conditioned by combined effects of the sedimentary petrofabric, lithology and stress conditions during the inversion of the basin in the Early to Middle Miocene.