Fault Zone Architecture and Permeability Distribution in the Neogene Clastics of Northern Sarawak (Miri Airport Road Outcrop), Malaysia
Rasoul Sorkhabi, Shutaro Hasegawa, 2005. "Fault Zone Architecture and Permeability Distribution in the Neogene Clastics of Northern Sarawak (Miri Airport Road Outcrop), Malaysia", Faults, Fluid Flow, and Petroleum Traps, Rasoul Sorkhabi, Yoshihiro Tsuji
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The Miri Airport Road outcrop in Miri, Sarawak, exposes a weakly consolidated sandstone-mudstone sequence of Miocene age in the form of a gentle anticline cut by a series of normal faults. An outcrop study of the normal faults shows that fault zones in porous sandstones are characterized by a combination of shale smear and anastomosing deformation bands. The continuity of shale smear on fault offset was observed as having a shale-smear factor (fault throw divided by shale layer thickness) of at least 5. Deformation bands occur as solitary planar structures in the host sandstone away from fault zones but increase markedly in density and linkage toward the fault slip plane, possibly indicating that faulting evolves from individual bands to a high-strain zone characterized by anastomosing deformation bands and culminating in the fault slip plane. Gas-permeability measurements show that individual deformation bands have an order of magnitude lower permeability than in the nearby sandstone matrix, and that the lowest permeability of fault zones defined by anastomosing deformation bands is in traverses nearly perpendicular to fault planes. It was found that the sandstone matrix in the fault zone has a lower permeability than individual deformation bands outside the fault zone, indicating that as a whole, the fault zone undergoes tectonic compaction and porosity collapse. The development of major normal faults was also accompanied by reactivation of bedding-perpendicular joints as small-displacement, simple-shear faults between the major faults.