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structural geology, propagation mechanics and - Stanford School of ...

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DB tip<br />

DB<br />

DBs<br />

Grains<br />

Pores<br />

Figure 6.2. Compactive deformation b<strong>and</strong>s (DBs) as seen in the Aztec s<strong>and</strong>stone, Valley<br />

Clay<br />

<strong>of</strong> Fire, NV. These DBs are tabular, bounded features <strong>of</strong> pore-loss compaction that<br />

typically crop out as systematic <strong>and</strong> <strong>of</strong>ten extensive arrays <strong>of</strong> resistant, positive-relief<br />

ridges within a relatively undeformed s<strong>and</strong>stone matrix (top). Individual b<strong>and</strong>s are<br />

approximately planar, displaying distinct tips even when closely spaced—width <strong>of</strong><br />

measuring tape is one inch (bottom left). Viewed in thin section, grain cracking,<br />

rearrangement <strong>and</strong> pore loss are readily apparent, illustrating why DBs act as barriers to<br />

fluid flow. Unlike many DBs, however, those in the Aztec tend to exhibit limited<br />

cataclasis <strong>and</strong> little or no net shear <strong>of</strong>fset (bottom right).<br />

145

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