Insights into microstructural and petrophysical properties of deformation bands in porous sandstone, Kachchh (Kutch) Rift Basin, India

Abstract

The study addresses how the deformation mechanisms influence the microstructural properties of deformation bands developed in high-porosity sandstones of the Kachchh (Kutch) Rift Basin (KRB), India. The KRB located at the western continental margin of the Indian plate is neotectonically active and is affected by the periodic reactivation of multiple ~W-striking dip-slip/strike-slip faults. We investigated the porous sandstones of Bhuj and Jhuran Formation, which contain cataclastic shear bands, disaggregation bands, and cementation bands. High-resolution optical and scanning electron microscopy images were used to analyze the microstructures, grain size and shape, and porosity for both the host rock and deformation bands. The cataclastic bands display preferential alignment of elongated grains parallel to the boundaries of deformation bands. The mechanisms of deformation are dominated by varying degrees of cataclasis and pressure solution that have caused grain reorganization, rolling, flaking of grain edges, and intragranular and transgranular fracturing. This resulted in grain size and porosity reduction within the deformation bands. The porosity loss in deformation bands is of three to five orders of magnitude compared to the host rock. The grain size distribution results are consistent with a power-law model that have low exponent (D) values between 0.89 and 1.00 for deformation bands. Our findings suggest that cataclasis within deformation bands appears to be dominant in the extensional stress state, however shear-related disaggregation of grains is observed in both extensional and compressional stress regimes.