Deformációs szalagok porózus, szemcsés kőzetekben

Abstract

Deformation bands are widespread strain localization structures in porous media. The main aim of this paper is to introduce these deformation elements giving an overview of their basic macroscopic characteristics, classification,
formation mechanisms and rheological evolution using published data and Hungarian field examples. Formation of deformation bands is influenced by numerous factors, such as porosity, rock fabric parameters (grain size, grain shape,
sorting), pore water content, lithification, degree of burial diagenesis, and loading path. Following the characterisation of deformation bands a description is given of the way which faults with a slip surface can be localized along clusters of
deformation bands during the mature phase of their evolution.
In the literature two main types of deformation band classification are widely accepted. One of them distinguishes five types, based on their kinematic aspects from dilational through shear variants to pure compactional ones. The other
classification separates four types on the basis of dominant deformation mechanism. These two types of classification reflect the stress and petrophysical conditions operating during deformation band formation.
Here, particular interest focuses on a special type of deformation band, namely solution band in carbonates, where dissolution is the main deformation mechanism. This type of bands has partly different features than those ones
developed in siliciclastics, this being due to the petrophysical properties of carbonates. Pressure solution is the prevailing deformation mechanism in carbonates which results in grain size and porosity reduction.
Some interesting Hungarian examples will be presented. Deformation bands were investigated on macro- and microscopic scales respectively, in porous sandstones and conglomerates from the Bükkalja area. Combined analysis of
fault slip data and deformation bands reveals the progressive evolution of the latter, thus reflecting a changing deformation mechanism with burial depth and also with cumulative displacement. It was concluded that the identified
‘less-destructive’ type of deformation band represents the earliest phase in their evolution. Upon burial diagenesis, the deformation became more destructive and formed more intense cataclasis with increasing displacements up to the point
of occurrence of the discrete slip surface (fault). This trend clearly corresponds to published data and its application should be tested in other sub-basins within the Pannonian basin system. On the applied geological side, deformation
bands have considerable effect on path of fluid flow; this is due to their reduced permeability and should be considered during future studies in the Pannonian Basin.