Permeability alteration in small-displacement faults in poorly lithified sediments: Rio Grande Rift, Central New Mexico

Are faults preferential flow paths through semiarid and arid vadose zones?

“…The porosity of deformation bands in sandstones is almost completely eliminated and saturated conductivity is reduced 1 -7 orders of magnitude (relative to the protolith) [Aydin, 1978;Fowles and Burley, 1994;Ogilvie et al, 2001]. Deformation bands in poorly lithified sands demonstrate saturated conductivity decreases of only 2 -4 orders of magnitude, and significant amounts of both macroporosity and microporosity remain [Sigda et al, 1999;Hong, 1999;Herrin, 2001]. Irrespective of the degree of protolith lithification, deformation processes create sizeable structures with very different saturated hydraulic properties than the surrounding matrix.…”

“…[3] One commonly observed type of deformation band is formed by cataclasis (grinding and breaking of grains) and compaction, even from displacements as small as a few millimeters [Aydin, 1978;Sigda et al, 1999;Cashman and Cashman, 2000;Taylor and Pollard, 2000;Herrin, 2001]. We do not consider noncataclastic deformation bands (i.e., compaction and dilation bands ]) because we have not observed them in the Rio Grande rift or found reports of their occurrence there in the literature.…”

“…We do not consider noncataclastic deformation bands (i.e., compaction and dilation bands ]) because we have not observed them in the Rio Grande rift or found reports of their occurrence there in the literature. Cataclasis and compaction drastically reduce mean pore size, increase clay-size fraction, and decrease sorting, thereby reducing porosity and saturated hydraulic conductivity relative to parent sandstone [Pittman, 1981;Ogilvie et al, 2001] or parent sand [Hong, 1999;Sigda et al, 1999]. The extent of reduction in porosity and saturated conductivity differs with degree of protolith (parent material) lithification.…”

“…This architecture differs substantially from the gouge-filled core zone and fracture-dominated damage zone architecture common to faults in crystalline rock [Smith et al, 1989] and from the core zone and deformation band-rich damage zone described for faults in well-lithified porous sandstones [Aydin, 1978;Caine et al, 1996]. Deformation bands and zones of deformation bands are common elements within the damage and mixed zones of larger displacement faults in poorly lithified sediments [Heynekamp et al, 1999;Rawling et al, 2001] and may be the only visible element in smaller displacement faults [Sigda et al, 1999;Herrin, 2001]. Deformation bands are narrow, quasi-tabular zones of localized deformation and diagenesis [Aydin, 1978;Pittman, 1981;Edwards et al, 1993;Sigda et al, 1999;Cashman and Cashman, 2000;Herrin, 2001].…”

“…Deformation bands and zones of deformation bands are common elements within the damage and mixed zones of larger displacement faults in poorly lithified sediments [Heynekamp et al, 1999;Rawling et al, 2001] and may be the only visible element in smaller displacement faults [Sigda et al, 1999;Herrin, 2001]. Deformation bands are narrow, quasi-tabular zones of localized deformation and diagenesis [Aydin, 1978;Pittman, 1981;Edwards et al, 1993;Sigda et al, 1999;Cashman and Cashman, 2000;Herrin, 2001]. Small displacement faults comprising only zones of deformation bands (called deformation band faults hereinafter) can be locally numerous and extensive, both laterally and vertically.…”