Changes

Both brittle sands and coals as well as ductile shales are incorporated in the fault zone. The mechanism of gouge formation is much more complex than a simple “smearing” of ductile shales into the fault zone. Although faults exhibit a complete spectrum of behavior from brittle to ductile, interbedded sand-shale sequences with strong ductility contrast commonly exhibit this transitional behavior.

Both brittle sands and coals as well as ductile shales are incorporated in the fault zone. The mechanism of gouge formation is much more complex than a simple “smearing” of ductile shales into the fault zone. Although faults exhibit a complete spectrum of behavior from brittle to ductile, interbedded sand-shale sequences with strong ductility contrast commonly exhibit this transitional behavior.

[[file:evaluating-top-and-fault-seal_fig10-20.png|thumb|{{figure number|10-20}}See text for explanation.]]

[[file:evaluating-top-and-fault-seal_fig10-20.jpg|thumb|{{figure number|10-20}}See text for explanation.]]

Shale-rich gouge zones can create impermeable barriers. The following, a normal fault in Jurassic and Triassic sediments near Lilstock, U.K., shows a gouge zone approximately [[length::5 m]] thick. The gouge consists predominantly of ductile shales and marls as well as small amounts of brittle limestones. Faults with similar shale-rich gouge in producing fields create seals.

Shale-rich gouge zones can create impermeable barriers. The following, a normal fault in Jurassic and Triassic sediments near Lilstock, U.K., shows a gouge zone approximately [[length::5 m]] thick. The gouge consists predominantly of ductile shales and marls as well as small amounts of brittle limestones. Faults with similar shale-rich gouge in producing fields create seals.