University of Texas at Austin

Morrison Formation, San Juan Basin (16)

Comments on Geologic Parameters

16 Rock Mineralogy:

The framework grains of the coarser grained sandstone of the "Westwater Canyon" ("Salt Wash" of Anderson and Lucas, 1995) Member consist mostly of quartz, microcline, sodium plagioclase, and lithic fragments of various types. The finer grained beds often consist of fine-grained sandstone, mudstone, and rare limestone nodules and lenses, but locally they are greenish-gray smectitic mudstones (Turner-Peterson, 1987). The Brushy Basin Member has similar lithology, but the ratio of coarse-grained beds versus finer grained material is significantly lower. Also, tuff beds containing a variety of authigenic minerals constitute a significant fraction of the Brushy Basin Member (Turner-Peterson, 1987). These authigenic minerals include mixed-layer illite-smectite, clinoptilolite, analcime, potassium feldspar, albite, silica in the form of quartz and chalcedony, and calcite. Much of the mudstone in the Brushy Basin Member is bentonitic. (Turner-Peterson, 1987).

16 Reference:

Turner-Peterson, C. E., 1987, Sedimentology of the Westwater Canyon and Brushy Basin Members, Upper Jurassic Morrison Formation, Colorado Plateau, and relationship to uranium mineralization: University of Colorado, Ph.D. dissertation, 169 p.


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