structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Although the Aztec s<strong>and</strong>stone experienced less than 1% total shortening as the result<br />
<strong>of</strong> CB formation, the low-porosity, low-permeability b<strong>and</strong> fabrics developed have been<br />
shown capable <strong>of</strong> exerting pr<strong>of</strong>ound fluid flow effects at scales <strong>of</strong> practical interest. The<br />
analysis presented here <strong>of</strong> CBs as indicators <strong>of</strong> paleostress <strong>and</strong> tectonic structure in this<br />
exhumed analog aquifer/reservoir also applies in reverse. That is, given knowledge <strong>of</strong> the<br />
stress <strong>and</strong> material history <strong>of</strong> a subsurface s<strong>and</strong>stone, predictions regarding the possible<br />
presence <strong>and</strong> geometry <strong>of</strong> CBs can be made.<br />
2. Introduction<br />
Compaction b<strong>and</strong>ing as a recognized mode <strong>of</strong> localized brittle failure in porous<br />
s<strong>and</strong>stone has a brief history, having first been described <strong>and</strong> named by Mollema <strong>and</strong><br />
Antonellini (1996) based on their work in the Navajo s<strong>and</strong>stone <strong>of</strong> south central Utah.<br />
Compaction b<strong>and</strong>s (CBs) represent one kinematic end member <strong>of</strong> the suite <strong>of</strong> structures<br />
known collectively as deformation b<strong>and</strong>s, which includes shear <strong>and</strong> dilation b<strong>and</strong>s (Du<br />
Bernard et al., 2002; Borja <strong>and</strong> Aydin, 2004). Mollema <strong>and</strong> Antonellini (1996) described<br />
CBs as long (meters), thin (centimeters) tabular zones <strong>of</strong> mechanical porosity loss formed<br />
within the compressional quadrants <strong>of</strong> shear b<strong>and</strong> style faults (Aydin, 1978), interpreting<br />
them as “a <strong>structural</strong> analog for anti-mode I cracks in æolian s<strong>and</strong>stone...that<br />
accommodate pure compaction,” following the conceptual anticrack model for pressure<br />
solution surfaces <strong>of</strong> Fletcher <strong>and</strong> Pollard (1981).<br />
The recognition <strong>of</strong> CBs, <strong>and</strong> their obvious potential to act as low-porosity, low-<br />
permeability impediments to fluid flow in otherwise highly transmissive s<strong>and</strong>stones, has<br />
excited an ongoing flurry <strong>of</strong> work both experimental (e.g. Olsson <strong>and</strong> Holcomb, 2000;<br />
Klein et al., 2001; Vajdova <strong>and</strong> Wong, 2003; Haimson, 2003; Baud et al., 2004; Tembe et<br />
al., 2006) <strong>and</strong> theoretical (e.g. Olsson, 1999; Issen <strong>and</strong> Rudnicki, 2000, 2001; Detournay<br />
et al., 2003; Bésuelle <strong>and</strong> Rudnicki, 2004; Rudnicki, 2002, 2003, 2004; Katsman et al.,<br />
2005; Rudnicki <strong>and</strong> Sternl<strong>of</strong>, 2005; Sternl<strong>of</strong> et al., 2005; Katsman <strong>and</strong> Aharonov, 2006)<br />
all <strong>of</strong> it aimed at comprehending the <strong>mechanics</strong> <strong>of</strong> compaction localization in porous,<br />
granular materials. To date, however, the only other field-based study published on CB<br />
occurrence <strong>and</strong> <strong>geology</strong> also focused on an æolian Jurassic s<strong>and</strong>stone <strong>of</strong> the southwestern<br />
U.S.—the Navajo-equivalent Aztec s<strong>and</strong>stone <strong>of</strong> southeastern Nevada (Sternl<strong>of</strong> et al.,<br />
2005). That paper presents an anticrack-inclusion mechanical model for CBs that is based<br />
10