The Westwater Canyon Member is one of several large, low-gradient alluvial fans that comprise the Morrison Formation in the Four Corners area. Morrison fans were deposited by major laterally migrating streams entering a broad basin bounded by highlands on the west and south. The Westwater sandstone framework consists of a down-fan succession of (1) proximal braided channel, (2) straight bedload-channel, (3) sinuous mixed load-channel, and (4) distributary mixed load-channel sandstone bodies. Regional sandstone distribution and facies patterns are highly digitate and radiate from a point source northwest of Gallup, New Mexico.

Early groundwater flow evolution within the Westwater fan aquifer system can be inferred by analogy with Quaternary wet-fan deposits and by the interpreted paragenetic sequence of diagenetic features present. Syndepositional flow was controlled by the down-fan hydrodynamic gradient and high horizontal and vertical transmissivity of the sand-rich fan aquifer. Groundwater was abundant, fresh, and slightly alkaline; dissolution and transport of soluble humate would be likely. With increasing confinement of the aquifer below less permeable tuffaceous Brushy Basin deposits and release of soluble constituents from volcanic ash, flow patterns stabilized and relatively more saline, pregnant groundwater permeated the aquifer. Uranium mineralization occurred during this early postdepositional, emiconfined flow phase. Exposure, erosion, and possible further flushing of proximal fan deposits had little apparent effect on the aquifer. Development of overlying Dakota swamps suggests a shallow water table indicative of regional discharge or stagnation. In either event, only limited downward flux of acidic water is recorded by local bleached, kaolinized zones where Westwater directly underlies the Dakota. Subsequent groundwater flow phases have further obscured primary alteration patterns and caused some local oxidation and redistribution of uranium.

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