Hydrogeologic heterogeneity of faulted and fractured Glass Mountain bedded tuffaceous sediments and ash-fall deposits: The Crucifix site near Bishop, California

Abstract

Lithologic, macrostructural, microstructural, geophysical, and in situ gas permeability data from a natural exposure of highly porous, faulted and fractured tuffaceous sediments and interbedded ash-fall deposits near Bishop, California, are presented and analyzed in relation to published geologic information. This natural analog study was motivated by the need to evaluate potential length scales over which lateral fl ow diversion might occur above and within the nonwelded Paintbrush Tuff at Yucca Mountain, Nevada. Lateral diversion of fl ow in the overlying Paintbrush Tuff was previously proposed by others as a natural barrier that might protect a proposed high-level radioactive waste and spent nuclear fuel repository from percolating water. Because the length scale for capillary barrier breakthrough and leakage is decreased in the presence of subvertical structural heterogeneities, we characterized a horst-bounding fault, small-displacement normal faults within a footwall deformation zone, and secondary heterogeneities within two beds dissected by the faults. Critical deformation-related features that may infl uence fl uid fl ow within bedded tuffaceous sediments include (1) permeability anisotropy imposed by steeply dipping faults and stratigraphic layering; (2) fault zone widths and styles, which are dependent on bed thickness and ash, glass, and clay content; and (3) fracture intensities and overprinting mechanisms (associated with fault deformation and vertical and nonvertical fracture orientations), which strongly infl uence the hydrogeologic heterogeneity of units they dissect. Microstructural analysis reveals structurally induced porosity variations at the micrometer to millimeter scale, gas permeability data show the infl uence of deformation on permeability at the centimeter to tens of centimeters scale, and resistivity and ground-penetrating radar data show lateral variations on the meter to tens of meters scale in horizontally bedded layers. All together, these observations and data show heterogeneity over seven orders of magnitude of length scale. Structurally enhanced porosity and permeability heterogeneities will tend to limit the length scale of lateral fl ow diversion, redirect fl ow downward, and enhance vertical fl uid movement within the vadose zone.

Observations on normal-fault scarp morphology and fault system evolution of the Bishop Tuff in the Volcanic Tableland, Owens Valley, California, U.S.A.

“…Faults in the underlying nonwelded Bishop Tuff show development of a narrow fault zone, with cataclasis and slickenline development consistent with shear failure in rock without a preexisting fracture fabric to reactivate (Evans and Bradbury, 2004;Dinwiddie et al, 2006Dinwiddie et al, , 2012McGinnis et al, 2009). Propagating as shear fractures through an unfractured medium, these faults developed as thin cataclastic shear zones with associated grain cataclasis and pore collapse.…”

“…Faulting in the Volcanic Tableland has been investigated to: (i) characterize normal fault displacement-length scaling relationships for faults and fault segments (Dawers et al, 1993;Dawers and Anders, 1995); (ii) test linear-elastic boundary element modeling of fault displacement patterns and related fault block geometry (Willemse et al, 1996;Willemse, 1997;Lovely et al, 2012); (iii) understand the formation, deformation, and breaching of relay ramps and resulting development of fault corrugation (Ferrill et al, 1999b;Ferrill and Morris, 2001); (iv) analyze fluvial channel response to relay-ramp-bounding fault displacements (Hopkins and Dawers, 2015); and (v) characterize the development of fault network connectivity (Sims et al, 2005). In Faulting in the Volcanic Tableland | RESEARCH addition, investigations have been performed to understand fault interaction, fault zone deformation processes, and influences of these processes on permeability within the Bishop Tuff and the underlying nonwelded tuff and volcaniclastic sediments (Ferrill et al, 2000Evans and Bradbury, 2004;Dinwiddie et al, 2006Dinwiddie et al, , 2012McGinnis et al, 2009).…”

Spatial distribution of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah: A mechanical analog for faulting in pyroclastic deposits on Mars

“…Valuable insight into the basic style of strain localization expected around faults in tuff can be gleaned from a variety of previous works. Based on studies of faulting in clay‐poor clastic sediments [e.g., Wong et al , 2003; Fossen et al , 2007and references therein] including non‐welded tuff [ Wilson et al , 2003; Evans and Bradbury , 2004; Dinwiddie et al , 2006; McGinnis et al , 2009; Riley et al , 2010; Dinwiddie et al , 2012], brittle deformation in poorly indurated pyroclastic materials is expected to be dominated by deformation band formation followed by frictional slip. Additionally, damage zones around faults in porous and granular sediments are expected to increase in width with increasing fault strain [e.g., Beach et al , 1999; Shipton and Cowie , 2003; McGinnis et al , 2009; Savage and Brodsky , 2011].…”

“…Despite such previous work in tuff and other mechanically analogous sediments, knowledge of both the character and spatial distribution of fault‐related inelastic strain in poorly indurated and fine‐grained tuff is sparse (but improving). Such insight is provided by studies of the Crucifix fault, a normal fault with a 7‐m offset in primary and reworked pyroclastic sediments that underlie the Bishop Tuff [ Ferrill et al , 2000; Evans and Bradbury , 2004; McGinnis et al , 2009; Dinwiddie et al , 2012]. These studies primarily focus on the temporal evolution, spatial distribution, and styles of strain localization within a ∼11 m wide swath across the Crucifix fault and its damage zone.…”

Registros de alta resolución de la conductividad hidráulica saturada en testigos de perforaciones usando mediciones de permeabilidad al aire

“…To avoid effects of weathering and seal quality 84 problems, the development and use of a small drill hole minipermeameter probe has also received 85 considerable attention (Dinwiddie et al , 2006(Dinwiddie et al , 2012Castle et al 2004). …”