Diagenetic control of deformation mechanisms in deformation bands in a carbonate grainstone

摘要

Deformation bands are commonly found in porous silicilastic sediments, where strain is accommodated by rotation, translation, and fracturing of individual grains instead of by the formation of a sharp discontinuity. We investigated deformation bands in a high-porosity carbonate rock from the Eisenstadt-Sopron Basin, on the border between Austria and Hungary, using a combination of microstructural and petrophysical methods. We used cadiodoluminescence and electron microprobe analyses to assess the distribution and chemical composition of the carbonate particles, deformation bands, and cements. The earliest deformation bands formed before the cementation of the limestone, mainly by rotation of elongated bioclasts to an orientation parallel to the deformation bands. Further movement along the bands after the generation of blocky cement around the bioclasts resulted in cataclastic deformation of both allochems and cement. Moreover, we documented a reduction of porosity from 22 to 35% in the host rock to 2 to 5% in the deformation bands by microcomputed tomography and conventional helium porosimetry. Permeability is reduced as much as three orders of magnitude relative to the host rock, as documented by pressure decay probe permea-metry. The observations indicate a change in physical properties of the rock caused by cementation during the generation of deformation bands, which results in a change of deformation mechanism from grain rotation and compaction to cataclastic deformation along a single band. The reduction of