Disconformities in Grants mineral belt and their relationship to uranium deposits
At least five major, regionally extensive disconformities are present in sedimentary rocks of Triassic, Jurassic, and Cretaceous age in the Grants mineral belt. These disconformities, some of which have been known for many years, have proven useful in stratigraphic correlation and in differentiation of lithologically and genetically similar rocks in the mineral belt and elsewhere on the Colorado Plateau. Two of these disconformities, one in the lower part of the Morrison Formation and the pre-Dakota Sandstone disconformity, are believed to be related to the distribution of sandstone-type uranium deposits in the Morrison Formation (Jurassic) and in the immediately overlying Dakota Sandstone (Cretaceous). The Westwater Canyon Member and laterally equivalent beds in the Recapture Member of the Morrison Formation are separated from underlying Jurassic rocks by an intraformational disconformity which marks a major change in depositional environment, from predominantly sabkha with eolian dunes below the disconformity to mixed fluvial and lacustrine above the disconformity. This disconformity is economically significant because all of the large uranium deposits in the Grants mineral belt occur in first-cycle arkosic fluvial sandstone of the Morrison above the disconformity. The pre-Dakota disconformity is a well-known, predominantly southward-beveling regional disconformity that marks the lower boundary of the Dakota throughout the San Juan Basin and adjacent regions. In the western part of the mineral belt, relatively impermeable siltstone of the Brushy Basin Member of the Morrison Formation has been truncated by pre-Dakota erosion at this disconformity, and uranium-bearing ground waters from the Morrison have migrated into basal organic-rich sandstone of the Dakota to produce several small-to medium-sized uranium deposits.
- Research Organization:
- Geological Survey, Denver, CO
- OSTI ID:
- 6385161
- Report Number(s):
- CONF-7905120-
- Journal Information:
- Mem. - N.M. Bur. Mines Miner. Resour.; (United States), Journal Name: Mem. - N.M. Bur. Mines Miner. Resour.; (United States) Vol. 38; ISSN NMMMA
- Country of Publication:
- United States
- Language:
- English
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COLORADO PLATEAU
CRETACEOUS PERIOD
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