VARIATION OF PORE FABRIC ACROSS A FOLD-THRUST STRUCTURE

Variations of pore orientation, pore shape, porosity, and hydraulic permeability, within a siltstone unit of a fold-thrust structure, are determined using magnetic pore fabric analysis, mercury injection porosimetry, and scanning electron microscopy (SEM). While samples in the foreland show evidence for the preservation of depositional pore geometry, the progressively deformed thrust sheet reveals increasingly oblate pore fabric anisotropy with microcrack planes oriented normal to the tectonic transport direction. Porosity, pore throat sizes, and permeability, show corresponding spatial variations across the structure. Independent of the deformation state within the trust sheet, pore and magnetic grain fabric correlate closely in orientation.