Abstract

Evidence for regional ground-water discharge from the lower Paleozoic carbonates via the Shay fault zone is largely circumstantial because springs associated with the discharge are now covered by Lake Powell. The following facts support such discharge. (1) Ground-water gradients in the lower Paleozoic carbonates converge on the outcrops of the Shay fault zone in the deep canyons of the Colorado River. (2) Bleached zones revealing the circulation of reducing waters are prevalent along the Shay fault zone. (3) One minor spring was observed by the writer to discharge poor quality H₂S water in Dark Canyon from fractures associated with the Shay fault zone.

Permeabilities at the level of the lower Paleozoic carbonates within the Shay fault zone are probably dominated by solution widened fractures in the otherwise poorly transmissive section. Evidence supporting this conclusion includes (1) drilled cavities in the Redwall Limestone in Placid Oil, USA #DU-2 along the Shay fault zone, (2) collapse structures developed along several of the deeply exposed faults in the zone, and (3) unusually small hydraulic gradients associated with ground-water circulation in the lower Paleozoic carbonates. Exposed caverns in the Eminence extensional fault zone in Marble Canyon, Arizona, appear to offer a good physical analog for highly permeable conditions that probably occur in the lower Paleozoic carbonates along the Shay fault zone.

The the Shay fault zone represents the regional discharge point for waters in the lower Paleozoic carbonate section under both the western part of the Paradox basin and under the entire Henry hydrologic basin. The Shay fault zone has served as a regional discharge point since before the incision of Cataract Canyon in late Miocene-early Pliocene time based on the presence of bleached faults that extend to the tops of the canyons of the Colorado River and which crop out on the Organ Rock Shale erosion surface east of Hite.